[libcamera-devel,1/2] ipa: Create a camera sensor helper class

12500 diff mbox series

Setting analogue gain for a specific sensor is not a straghtforward
operation, as one needs to know how the gain is calculated for it.

This commit introduces a new camera sensor helper in libipa which aims
to solve this specific issue.
It is based on the MIPI alliance Specification for Camera Command Set
and implements, for now, only the analogue "Global gain" mode.

Is makes it possible to only have 4 parameters to store per sensor, and
the gain calculation is then done identically for all of them. This
commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
ov5693.

Adding a new sensor is pretty straightfoward as one only needs to
implement the sub-class for it and register that class to the
CameraSensorHelperFactory.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
---
 src/ipa/libipa/camera_sensor_helper.cpp | 361 ++++++++++++++++++++++++
 src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
 src/ipa/libipa/meson.build              |   2 +
 3 files changed, 454 insertions(+)
 create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
 create mode 100644 src/ipa/libipa/camera_sensor_helper.h

Hello Jean-Michel,


On Mon, Jun 07, 2021 at 02:35:32PM +0200, Jean-Michel Hautbois wrote:
> Setting analogue gain for a specific sensor is not a straghtforward
> operation, as one needs to know how the gain is calculated for it.

Please bear with my poor understanding of the issue, but looking at
the code it doesn't seem the different is in how the gain is
calculated but rather in which constant parameters are used.

>
> This commit introduces a new camera sensor helper in libipa which aims
> to solve this specific issue.
> It is based on the MIPI alliance Specification for Camera Command Set
> and implements, for now, only the analogue "Global gain" mode.
>

I should first go through this document, so I'll probably have only
drive-by comments and nits here and there

> Is makes it possible to only have 4 parameters to store per sensor, and
> the gain calculation is then done identically for all of them. This
> commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
> ov5693.
>
> Adding a new sensor is pretty straightfoward as one only needs to
> implement the sub-class for it and register that class to the
> CameraSensorHelperFactory.

As asked offline, the current fatory implementation is the same as the
one we have for pipeline handlers, which requires static
initialization to make sure they are registered at library
initialization time. I suspect without this requirement the factory
here could be made simpler, but that's minor...

>
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 361 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 454 insertions(+)
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.h
>
> diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
> new file mode 100644
> index 00000000..2bd82861
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,361 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021 Ideas On Board
> + *
> + * camera_sensor_helper.cpp - helper class providing camera informations

Nit: 'Helper'
as I've received the same comment multiple times, 'information' is
uncountable, so no plural

> + */
> +#include "camera_sensor_helper.h"
> +
> +#include <map>
> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Create helper class for each sensor
> + *
> + * Each camera sensor supported by libcamera may need specific informations to
> + * be sent (analogue gain is sensor dependant for instance).
> + *
> + * Every subclass of CameraSensorHelper shall be registered with libipa using
> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> +
> +namespace ipa {
> +
> +/**
> + * \class CameraSensorHelper
> + * \brief Create and give helpers for each camera sensor in the pipeline

I would here and maybe above in the file description drop the 'create
and give' part. The CameraSensorHelper base class computes sensor
tuning parameters using sensor-specific constants. The factory instead
does the actual object creation

> + *
 sensor-specific constants. The factory instead does the actual object
 creation

> + * CameraSensorHelper instances are unique and sensor dependant.

Is the base class meant to be used as a default if not sensor-specific
sub-class is registered ?

> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + * \param[in] name The sensor model name
> + *
> + * The CameraSensorHelper instances shall never be constructed manually, but always
> + * through the CameraSensorHelperFactory::create() method implemented by the
> + * respective factories.
> + */
> +

Empty line

> +CameraSensorHelper::CameraSensorHelper(const char *name)
> +	: name_(name)
> +{
> +	analogueGain_ = { GlobalGain, 1, 1, 0, 0 };
> +}

I wonder, we don't support AlternateGlobalGain at the moment, do you
expect it to be required soon ?

> +
> +CameraSensorHelper::~CameraSensorHelper()
> +{
> +}
> +
> +/**
> + * \fn CameraSensorHelper::getGainCode(double gain)

If you document the function just defined below, you don't need the
\fn anchor

Library-wide we don't use 'get' for getters, so this might just be
gainCode() ?

> + * \brief Get the analogue gain code to pass to V4L2 subdev control

Aren't we computing the gain code from the analogue gain value ?

> + * \param[in] gain The real gain to pass
> + *
> + * This function aims to abstract the calculation of the gain letting the IPA
> + * use the real gain for its estimations.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).

Do you mean the m0, c0, etc etc paramteres ? Maybe this is better
specified in the enum documentation ?

> + */
> +uint32_t CameraSensorHelper::getGainCode(double gain) const
> +{
> +	/* \todo we only support the global gain mode for now */
> +	if (analogueGain_.type != GlobalGain)
> +		return UINT32_MAX;
> +
> +	if (analogueGain_.m0 == 0)
> +		return (analogueGain_.c0 - gain * analogueGain_.c1) / (gain * analogueGain_.m1);
> +	if (analogueGain_.m1 == 0)
> +	return (gain * analogueGain_.c1 - analogueGain_.c0) / analogueGain_.m0;

You can break the two lines

> +
> +	LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";
> +	return 1;

Aren't the two error conditions verified by assertions ? Otherwise we
return two different error codes (MAXINT and 1) which are difficult to
identify.

> +}
> +
> +/**
> + * \fn CameraSensorHelper::getGain
> + * \brief Get the real gain from the V4l2 subdev control gain
> + * \param[in] gainCode The V4l2 subdev control gain
> + *
> + * This function aims to abstract the calculation of the gain letting the IPA
> + * use the real gain for its estimations. It is the counterpart of the function
> + * CameraSensorHelper::getGainCode.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).

Same comments as above

> + */
> +double CameraSensorHelper::getGain(uint32_t gainCode) const
> +{
> +	if (analogueGain_.type != GlobalGain)
> +		return UINT32_MAX;
> +
> +	if (analogueGain_.m0 == 0)
> +		return analogueGain_.c0 / (analogueGain_.m1 * gainCode + analogueGain_.c1);
> +	if (analogueGain_.m1 == 0)
> +		return (analogueGain_.m0 * gainCode + analogueGain_.c0) / analogueGain_.c1;
> +
> +	LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";
> +	return 1.0;
> +}

ditto

Also, these smells like static functions as they only use class
members constants for computations and do not hold any state. This
however does not play well with the class hierarchy...

> +
> +/**
> + * \fn CameraSensorHelper::name()
> + * \brief Retrieve the camera sensor helper name
> + * \return The camera sensor helper name
> + */
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainCapability
> + * \brief Specify the Gain mode supported by the sensor
> + *
> + * Describes the image sensor analog Gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::GlobalGain
> + * \brief Sensor supports Global gain
> + *
> + * The relationship between the integer Gain parameter and the resulting Gain
> + * multiplier is given by the following equation:
> + *
> + * \f$\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants exposed by the sensor.
> + * These constants are static parameters, and for any given image sensor either
> + * m0 or m1 shall be zero.
> + *
> + * The full Gain equation therefore reduces to either:
> + *
> + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> + */
> +
> +/**
> + * \var CameraSensorHelper::AlternateGlobalGain
> + * \brief Sensor supports Analogue Global gain (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analog Gain is also available.
> + * If the image sensor supports it, then the global analog Gain can be controlled
> + * by linear and exponential gain formula:
> + *
> + * \f$gain = analogLinearGainGlobal * 2^{analogExponentialGainGlobal} \f$
> + * \todo not implemented in libipa
> + */
> +
> +/**
> + * \struct CameraSensorHelper::analogueGainConstants
> + * \brief Analogue gain constants used for gain calculation
> + */

How do you envision this class to evolve ? I mean, it will go beyoind
just analogue gain calculations ? As otherwise a single class with a
map of sensor specific gain constants would do...

> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::type
> + * \brief Analogue gain coding type
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::m0
> + * \brief Constant used in the analog Gain control coding/decoding.
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::c0
> + * \brief Constant used in the analog Gain control coding/decoding.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::m1
> + * \brief Constant used in the analog Gain control coding/decoding.

Nit: briefs do not end with '.'

> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::c1
> + * \brief Constant used in the analog Gain control coding/decoding.

I presume I have to read the CCS specs to know what this parameters
actually are :)

> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGain_

Maybe something in the name that makes it clear these are params ?
Analouge gain to me is what 'getGain()' calculates, am I mistaken ?

> + * \brief The analogue gain parameters used for calculation
> + *
> + * The analogue gain is calculated through a formula, and its parameters are
> + * sensor specific. Use this variable to store the values at init time.
> + *

Empty line

> + */
> +

I'll skip the factory review for now

> +/**

[snip]

> +
> +/**
> + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
> + * \brief Construct a CameraSensorHelperImx219 instance for imx219
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperImx219(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)

I would add an empty line here and make it look like

class CameraSensorHelperXYZ : public CameraSensorHelper
{
public:
	CameraSensorHelperXYZ(const char *name)
        {
                ...
        }
};
REGISTER_CAMERA_SENSOR_HELPER("XYZ", CameraSensorHelperXYZ)


> +CameraSensorHelperImx219::CameraSensorHelperImx219(const char *name)
> +	: CameraSensorHelper(name)
> +{
> +	analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
> +}
> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
> + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5670(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char *name)
> +	: CameraSensorHelper(name)
> +{
> +	analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
> +}
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
> + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5693(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char *name)
> +	: CameraSensorHelper(name)
> +{
> +	analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
> +}
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> +
> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
> new file mode 100644
> index 00000000..63031902
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021 Ideas On Board
> + *
> + * camera_sensor_helper.h - helper class providing camera informations
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <string>
> +
> +#include <libcamera/class.h>
> +#include <libcamera/object.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper;
> +
> +class CameraSensorHelper : public Object
> +{
> +public:
> +	CameraSensorHelper(const char *name);
> +	virtual ~CameraSensorHelper();
> +
> +	const std::string &name() const { return name_; }
> +	uint32_t getGainCode(double gain) const;
> +	double getGain(uint32_t gainCode) const;
> +
> +protected:
> +	enum AnalogueGainCapability : uint16_t {
> +		GlobalGain = 0,
> +		AlternateGlobalGain = 2,

Are the gain type values defined by the CCS specs ?

> +	};
> +
> +	struct analogueGainConstants {
> +		uint16_t type;
> +		int16_t m0;
> +		int16_t c0;
> +		int16_t m1;
> +		int16_t c1;
> +	};
> +	analogueGainConstants analogueGain_;
> +
> +private:
> +	std::string name_;
> +	friend class CameraSensorHelperFactory;

Do you need this friend class declaration ?
The constructor is public...

> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +	CameraSensorHelperFactory(const char *name);
> +	virtual ~CameraSensorHelperFactory() = default;
> +
> +	std::unique_ptr<CameraSensorHelper> create();
> +
> +	const std::string &name() const { return name_; }
> +
> +	static void registerType(CameraSensorHelperFactory *factory);
> +	static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +private:
> +	virtual CameraSensorHelper *createInstance() = 0;
> +
> +	std::string name_;
> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)                        \
> +	class handler##Factory final : public CameraSensorHelperFactory     \
> +	{                                                                   \
> +	public:                                                             \
> +		handler##Factory() : CameraSensorHelperFactory(#handler) {} \
> +                                                                            \
> +	private:                                                            \
> +		CameraSensorHelper *createInstance()                        \
> +		{                                                           \
> +			return new handler(name);                           \
> +		}                                                           \
> +	};                                                                  \
> +	static handler##Factory global_##handler##Factory;
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
> +

No empty line at EOF otherwise git am complains (at least, that's how
I interpret the error message :)

Thanks
   j

> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> index 038fc490..dc90542c 100644
> --- a/src/ipa/libipa/meson.build
> +++ b/src/ipa/libipa/meson.build
> @@ -2,11 +2,13 @@
>
>  libipa_headers = files([
>      'algorithm.h',
> +    'camera_sensor_helper.h',
>      'histogram.h'
>  ])
>
>  libipa_sources = files([
>      'algorithm.cpp',
> +    'camera_sensor_helper.cpp',
>      'histogram.cpp'
>  ])
>
> --
> 2.30.2
>

Hi Jean-Michel,



On Mon, 7 Jun 2021 at 13:35, Jean-Michel Hautbois <
jeanmichel.hautbois@ideasonboard.com> wrote:

> Setting analogue gain for a specific sensor is not a straghtforward
> operation, as one needs to know how the gain is calculated for it.
>
> This commit introduces a new camera sensor helper in libipa which aims
> to solve this specific issue.
> It is based on the MIPI alliance Specification for Camera Command Set
> and implements, for now, only the analogue "Global gain" mode.
>

I know this has probably been discussed in detail internally, but what
provisions
do you expect for gain formulas that do not conform to the CCI formula, or
those
that are entirely table based?

Thanks,
Naush


> Is makes it possible to only have 4 parameters to store per sensor, and
> the gain calculation is then done identically for all of them. This
> commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
> ov5693.
>
> Adding a new sensor is pretty straightfoward as one only needs to
> implement the sub-class for it and register that class to the
> CameraSensorHelperFactory.
>
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 361 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 454 insertions(+)
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.h
>
> diff --git a/src/ipa/libipa/camera_sensor_helper.cpp
> b/src/ipa/libipa/camera_sensor_helper.cpp
> new file mode 100644
> index 00000000..2bd82861
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,361 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021 Ideas On Board
> + *
> + * camera_sensor_helper.cpp - helper class providing camera informations
> + */
> +#include "camera_sensor_helper.h"
> +
> +#include <map>
> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Create helper class for each sensor
> + *
> + * Each camera sensor supported by libcamera may need specific
> informations to
> + * be sent (analogue gain is sensor dependant for instance).
> + *
> + * Every subclass of CameraSensorHelper shall be registered with libipa
> using
> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> +
> +namespace ipa {
> +
> +/**
> + * \class CameraSensorHelper
> + * \brief Create and give helpers for each camera sensor in the pipeline
> + *
> + * CameraSensorHelper instances are unique and sensor dependant.
> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + * \param[in] name The sensor model name
> + *
> + * The CameraSensorHelper instances shall never be constructed manually,
> but always
> + * through the CameraSensorHelperFactory::create() method implemented by
> the
> + * respective factories.
> + */
> +
> +CameraSensorHelper::CameraSensorHelper(const char *name)
> +       : name_(name)
> +{
> +       analogueGain_ = { GlobalGain, 1, 1, 0, 0 };
> +}
> +
> +CameraSensorHelper::~CameraSensorHelper()
> +{
> +}
> +
> +/**
> + * \fn CameraSensorHelper::getGainCode(double gain)
> + * \brief Get the analogue gain code to pass to V4L2 subdev control
> + * \param[in] gain The real gain to pass
> + *
> + * This function aims to abstract the calculation of the gain letting the
> IPA
> + * use the real gain for its estimations.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + */
> +uint32_t CameraSensorHelper::getGainCode(double gain) const
> +{
> +       /* \todo we only support the global gain mode for now */
> +       if (analogueGain_.type != GlobalGain)
> +               return UINT32_MAX;
> +
> +       if (analogueGain_.m0 == 0)
> +               return (analogueGain_.c0 - gain * analogueGain_.c1) /
> (gain * analogueGain_.m1);
> +       if (analogueGain_.m1 == 0)
> +               return (gain * analogueGain_.c1 - analogueGain_.c0) /
> analogueGain_.m0;
> +
> +       LOG(CameraSensorHelper, Error) << "For any given image sensor
> either m0 or m1 shall be zero.";
> +       return 1;
> +}
> +
> +/**
> + * \fn CameraSensorHelper::getGain
> + * \brief Get the real gain from the V4l2 subdev control gain
> + * \param[in] gainCode The V4l2 subdev control gain
> + *
> + * This function aims to abstract the calculation of the gain letting the
> IPA
> + * use the real gain for its estimations. It is the counterpart of the
> function
> + * CameraSensorHelper::getGainCode.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + */
> +double CameraSensorHelper::getGain(uint32_t gainCode) const
> +{
> +       if (analogueGain_.type != GlobalGain)
> +               return UINT32_MAX;
> +
> +       if (analogueGain_.m0 == 0)
> +               return analogueGain_.c0 / (analogueGain_.m1 * gainCode +
> analogueGain_.c1);
> +       if (analogueGain_.m1 == 0)
> +               return (analogueGain_.m0 * gainCode + analogueGain_.c0) /
> analogueGain_.c1;
> +
> +       LOG(CameraSensorHelper, Error) << "For any given image sensor
> either m0 or m1 shall be zero.";
> +       return 1.0;
> +}
> +
> +/**
> + * \fn CameraSensorHelper::name()
> + * \brief Retrieve the camera sensor helper name
> + * \return The camera sensor helper name
> + */
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainCapability
> + * \brief Specify the Gain mode supported by the sensor
> + *
> + * Describes the image sensor analog Gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::GlobalGain
> + * \brief Sensor supports Global gain
> + *
> + * The relationship between the integer Gain parameter and the resulting
> Gain
> + * multiplier is given by the following equation:
> + *
> + * \f$\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants exposed by the sensor.
> + * These constants are static parameters, and for any given image sensor
> either
> + * m0 or m1 shall be zero.
> + *
> + * The full Gain equation therefore reduces to either:
> + *
> + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> + */
> +
> +/**
> + * \var CameraSensorHelper::AlternateGlobalGain
> + * \brief Sensor supports Analogue Global gain (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analog Gain is also available.
> + * If the image sensor supports it, then the global analog Gain can be
> controlled
> + * by linear and exponential gain formula:
> + *
> + * \f$gain = analogLinearGainGlobal * 2^{analogExponentialGainGlobal} \f$
> + * \todo not implemented in libipa
> + */
> +
> +/**
> + * \struct CameraSensorHelper::analogueGainConstants
> + * \brief Analogue gain constants used for gain calculation
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::type
> + * \brief Analogue gain coding type
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::m0
> + * \brief Constant used in the analog Gain control coding/decoding.
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::c0
> + * \brief Constant used in the analog Gain control coding/decoding.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::m1
> + * \brief Constant used in the analog Gain control coding/decoding.
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::c1
> + * \brief Constant used in the analog Gain control coding/decoding.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGain_
> + * \brief The analogue gain parameters used for calculation
> + *
> + * The analogue gain is calculated through a formula, and its parameters
> are
> + * sensor specific. Use this variable to store the values at init time.
> + *
> + */
> +
> +/**
> + * \class CameraSensorHelperFactory
> + * \brief Registration of CameraSensorHelperFactory classes and creation
> of instances
> + *
> + * To facilitate discovery and instantiation of CameraSensorHelper
> classes, the
> + * CameraSensorHelperFactory class maintains a registry of camera sensor
> helper
> + * classes. Each CameraSensorHelper subclass shall register itself using
> the
> + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create a
> corresponding
> + * instance of a CameraSensorHelperFactory subclass and register it with
> the
> + * static list of factories.
> + */
> +
> +/**
> + * \brief Construct a camera sensor helper factory
> + * \param[in] name Name of the camera sensor helper class
> + *
> + * Creating an instance of the factory registers it with the global list
> of
> + * factories, accessible through the factories() function.
> + *
> + * The factory \a name is used for debug purpose and shall be unique.
> + */
> +
> +CameraSensorHelperFactory::CameraSensorHelperFactory(const char *name)
> +       : name_(name)
> +{
> +       registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the CameraSensorHelper corresponding to
> the factory
> + *
> + * \return A unique pointer to a new instance of the CameraSensorHelper
> subclass
> + * corresponding to the factory
> + */
> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create()
> +{
> +       CameraSensorHelper *handler = createInstance();
> +       return std::unique_ptr<CameraSensorHelper>(handler);
> +}
> +
> +/**
> + * \fn CameraSensorHelperFactory::name()
> + * \brief Retrieve the factory name
> + * \return The factory name
> + */
> +
> +/**
> + * \brief Add a camera sensor helper class to the registry
> + * \param[in] factory Factory to use to construct the camera sensor helper
> + *
> + * The caller is responsible to guarantee the uniqueness of the camera
> sensor helper
> + * name.
> + */
> +void CameraSensorHelperFactory::registerType(CameraSensorHelperFactory
> *factory)
> +{
> +       std::vector<CameraSensorHelperFactory *> &factories =
> CameraSensorHelperFactory::factories();
> +
> +       factories.push_back(factory);
> +}
> +
> +/**
> + * \brief Retrieve the list of all camera sensor helper factories
> + *
> + * The static factories map is defined inside the function to ensures it
> gets
> + * initialized on first use, without any dependency on link order.
> + *
> + * \return The list of camera sensor helper factories
> + */
> +std::vector<CameraSensorHelperFactory *>
> &CameraSensorHelperFactory::factories()
> +{
> +       static std::vector<CameraSensorHelperFactory *> factories;
> +       return factories;
> +}
> +
> +/**
> + * \fn CameraSensorHelperFactory::createInstance()
> + * \brief Create an instance of the CameraSensorHelper corresponding to
> the factory
> + *
> + * This virtual function is implemented by the
> REGISTER_CAMERA_SENSOR_HELPER()
> + * macro. It creates a camera sensor helper instance associated with the
> camera
> + * sensor model.
> + *
> + * \return A pointer to a newly constructed instance of the
> CameraSensorHelper
> + * subclass corresponding to the factory
> + */
> +
> +/**
> + * \def REGISTER_CAMERA_SENSOR_HELPER
> + * \brief Register a camera sensor helper with the camera sensor helper
> factory
> + * \param[in] name Sensor model name used to register the class
> + * \param[in] handler Class name of CameraSensorHelper derived class to
> register
> + *
> + * Register a CameraSensorHelper subclass with the factory and make it
> available to
> + * try and match devices.
> + */
> +
> +/**
> + * \class CameraSensorHelperImx219
> + * \brief Create and give helpers for the imx219 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
> + * \brief Construct a CameraSensorHelperImx219 instance for imx219
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +       CameraSensorHelperImx219(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> +CameraSensorHelperImx219::CameraSensorHelperImx219(const char *name)
> +       : CameraSensorHelper(name)
> +{
> +       analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
> +}
> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
> + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +       CameraSensorHelperOv5670(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char *name)
> +       : CameraSensorHelper(name)
> +{
> +       analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
> +}
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
> + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +       CameraSensorHelperOv5693(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char *name)
> +       : CameraSensorHelper(name)
> +{
> +       analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
> +}
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> +
> diff --git a/src/ipa/libipa/camera_sensor_helper.h
> b/src/ipa/libipa/camera_sensor_helper.h
> new file mode 100644
> index 00000000..63031902
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021 Ideas On Board
> + *
> + * camera_sensor_helper.h - helper class providing camera informations
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <string>
> +
> +#include <libcamera/class.h>
> +#include <libcamera/object.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper;
> +
> +class CameraSensorHelper : public Object
> +{
> +public:
> +       CameraSensorHelper(const char *name);
> +       virtual ~CameraSensorHelper();
> +
> +       const std::string &name() const { return name_; }
> +       uint32_t getGainCode(double gain) const;
> +       double getGain(uint32_t gainCode) const;
> +
> +protected:
> +       enum AnalogueGainCapability : uint16_t {
> +               GlobalGain = 0,
> +               AlternateGlobalGain = 2,
> +       };
> +
> +       struct analogueGainConstants {
> +               uint16_t type;
> +               int16_t m0;
> +               int16_t c0;
> +               int16_t m1;
> +               int16_t c1;
> +       };
> +       analogueGainConstants analogueGain_;
> +
> +private:
> +       std::string name_;
> +       friend class CameraSensorHelperFactory;
> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +       CameraSensorHelperFactory(const char *name);
> +       virtual ~CameraSensorHelperFactory() = default;
> +
> +       std::unique_ptr<CameraSensorHelper> create();
> +
> +       const std::string &name() const { return name_; }
> +
> +       static void registerType(CameraSensorHelperFactory *factory);
> +       static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +private:
> +       virtual CameraSensorHelper *createInstance() = 0;
> +
> +       std::string name_;
> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)
>   \
> +       class handler##Factory final : public CameraSensorHelperFactory
>  \
> +       {
>  \
> +       public:
>  \
> +               handler##Factory() : CameraSensorHelperFactory(#handler)
> {} \
> +
>   \
> +       private:
>   \
> +               CameraSensorHelper *createInstance()
>   \
> +               {
>  \
> +                       return new handler(name);
>  \
> +               }
>  \
> +       };
>   \
> +       static handler##Factory global_##handler##Factory;
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
> +
> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> index 038fc490..dc90542c 100644
> --- a/src/ipa/libipa/meson.build
> +++ b/src/ipa/libipa/meson.build
> @@ -2,11 +2,13 @@
>
>  libipa_headers = files([
>      'algorithm.h',
> +    'camera_sensor_helper.h',
>      'histogram.h'
>  ])
>
>  libipa_sources = files([
>      'algorithm.cpp',
> +    'camera_sensor_helper.cpp',
>      'histogram.cpp'
>  ])
>
> --
> 2.30.2
>
>

Hi Naushir,

On 07/06/2021 19:31, Naushir Patuck wrote:
> Hi Jean-Michel,
> 
> 
> 
> On Mon, 7 Jun 2021 at 13:35, Jean-Michel Hautbois
> <jeanmichel.hautbois@ideasonboard.com
> <mailto:jeanmichel.hautbois@ideasonboard.com>> wrote:
> 
>     Setting analogue gain for a specific sensor is not a straghtforward
>     operation, as one needs to know how the gain is calculated for it.
> 
>     This commit introduces a new camera sensor helper in libipa which aims
>     to solve this specific issue.
>     It is based on the MIPI alliance Specification for Camera Command Set
>     and implements, for now, only the analogue "Global gain" mode.
> 
> 
> I know this has probably been discussed in detail internally, but what
> provisions
> do you expect for gain formulas that do not conform to the CCI formula,
> or  those
> that are entirely table based?

It has not been discussed in detail no, and I am sure I have missed a
lot of cases.
For those specific cases, we may, for instance, have a new value in
AnalogueGainCapability enum and let the subclass calculate the proper
value ?
I don't have this case right now in my hands, so it is difficult to know
precisely what is the best way to do so ;-).

> Thanks,
> Naush
> 
> 
>     Is makes it possible to only have 4 parameters to store per sensor, and
>     the gain calculation is then done identically for all of them. This
>     commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
>     ov5693.
> 
>     Adding a new sensor is pretty straightfoward as one only needs to
>     implement the sub-class for it and register that class to the
>     CameraSensorHelperFactory.
> 
>     Signed-off-by: Jean-Michel Hautbois
>     <jeanmichel.hautbois@ideasonboard.com
>     <mailto:jeanmichel.hautbois@ideasonboard.com>>
>     ---
>      src/ipa/libipa/camera_sensor_helper.cpp | 361 ++++++++++++++++++++++++
>      src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
>      src/ipa/libipa/meson.build              |   2 +
>      3 files changed, 454 insertions(+)
>      create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
>      create mode 100644 src/ipa/libipa/camera_sensor_helper.h
> 
>     diff --git a/src/ipa/libipa/camera_sensor_helper.cpp
>     b/src/ipa/libipa/camera_sensor_helper.cpp
>     new file mode 100644
>     index 00000000..2bd82861
>     --- /dev/null
>     +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>     @@ -0,0 +1,361 @@
>     +/* SPDX-License-Identifier: BSD-2-Clause */
>     +/*
>     + * Copyright (C) 2021 Ideas On Board
>     + *
>     + * camera_sensor_helper.cpp - helper class providing camera
>     informations
>     + */
>     +#include "camera_sensor_helper.h"
>     +
>     +#include <map>
>     +
>     +#include "libcamera/internal/log.h"
>     +
>     +/**
>     + * \file camera_sensor_helper.h
>     + * \brief Create helper class for each sensor
>     + *
>     + * Each camera sensor supported by libcamera may need specific
>     informations to
>     + * be sent (analogue gain is sensor dependant for instance).
>     + *
>     + * Every subclass of CameraSensorHelper shall be registered with
>     libipa using
>     + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
>     + */
>     +
>     +namespace libcamera {
>     +
>     +LOG_DEFINE_CATEGORY(CameraSensorHelper)
>     +
>     +namespace ipa {
>     +
>     +/**
>     + * \class CameraSensorHelper
>     + * \brief Create and give helpers for each camera sensor in the
>     pipeline
>     + *
>     + * CameraSensorHelper instances are unique and sensor dependant.
>     + */
>     +
>     +/**
>     + * \brief Construct a CameraSensorHelper instance
>     + * \param[in] name The sensor model name
>     + *
>     + * The CameraSensorHelper instances shall never be constructed
>     manually, but always
>     + * through the CameraSensorHelperFactory::create() method
>     implemented by the
>     + * respective factories.
>     + */
>     +
>     +CameraSensorHelper::CameraSensorHelper(const char *name)
>     +       : name_(name)
>     +{
>     +       analogueGain_ = { GlobalGain, 1, 1, 0, 0 };
>     +}
>     +
>     +CameraSensorHelper::~CameraSensorHelper()
>     +{
>     +}
>     +
>     +/**
>     + * \fn CameraSensorHelper::getGainCode(double gain)
>     + * \brief Get the analogue gain code to pass to V4L2 subdev control
>     + * \param[in] gain The real gain to pass
>     + *
>     + * This function aims to abstract the calculation of the gain
>     letting the IPA
>     + * use the real gain for its estimations.
>     + *
>     + * The parameters come from the MIPI Alliance Camera Specification for
>     + * Camera Command Set (CCS).
>     + */
>     +uint32_t CameraSensorHelper::getGainCode(double gain) const
>     +{
>     +       /* \todo we only support the global gain mode for now */
>     +       if (analogueGain_.type != GlobalGain)
>     +               return UINT32_MAX;
>     +
>     +       if (analogueGain_.m0 == 0)
>     +               return (analogueGain_.c0 - gain * analogueGain_.c1)
>     / (gain * analogueGain_.m1);
>     +       if (analogueGain_.m1 == 0)
>     +               return (gain * analogueGain_.c1 - analogueGain_.c0)
>     / analogueGain_.m0;
>     +
>     +       LOG(CameraSensorHelper, Error) << "For any given image
>     sensor either m0 or m1 shall be zero.";
>     +       return 1;
>     +}
>     +
>     +/**
>     + * \fn CameraSensorHelper::getGain
>     + * \brief Get the real gain from the V4l2 subdev control gain
>     + * \param[in] gainCode The V4l2 subdev control gain
>     + *
>     + * This function aims to abstract the calculation of the gain
>     letting the IPA
>     + * use the real gain for its estimations. It is the counterpart of
>     the function
>     + * CameraSensorHelper::getGainCode.
>     + *
>     + * The parameters come from the MIPI Alliance Camera Specification for
>     + * Camera Command Set (CCS).
>     + */
>     +double CameraSensorHelper::getGain(uint32_t gainCode) const
>     +{
>     +       if (analogueGain_.type != GlobalGain)
>     +               return UINT32_MAX;
>     +
>     +       if (analogueGain_.m0 == 0)
>     +               return analogueGain_.c0 / (analogueGain_.m1 *
>     gainCode + analogueGain_.c1);
>     +       if (analogueGain_.m1 == 0)
>     +               return (analogueGain_.m0 * gainCode +
>     analogueGain_.c0) / analogueGain_.c1;
>     +
>     +       LOG(CameraSensorHelper, Error) << "For any given image
>     sensor either m0 or m1 shall be zero.";
>     +       return 1.0;
>     +}
>     +
>     +/**
>     + * \fn CameraSensorHelper::name()
>     + * \brief Retrieve the camera sensor helper name
>     + * \return The camera sensor helper name
>     + */
>     +
>     +/**
>     + * \enum CameraSensorHelper::AnalogueGainCapability
>     + * \brief Specify the Gain mode supported by the sensor
>     + *
>     + * Describes the image sensor analog Gain capabilities.
>     + * Two modes are possible, depending on the sensor: Global and
>     Alternate.
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::GlobalGain
>     + * \brief Sensor supports Global gain
>     + *
>     + * The relationship between the integer Gain parameter and the
>     resulting Gain
>     + * multiplier is given by the following equation:
>     + *
>     + * \f$\frac{m0x+c0}{m1x+c1}\f$
>     + *
>     + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
>     + * image-sensor-specific constants exposed by the sensor.
>     + * These constants are static parameters, and for any given image
>     sensor either
>     + * m0 or m1 shall be zero.
>     + *
>     + * The full Gain equation therefore reduces to either:
>     + *
>     + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::AlternateGlobalGain
>     + * \brief Sensor supports Analogue Global gain (introduced in CCS v1.1)
>     + *
>     + * Starting with CCS v1.1, Alternate Global Analog Gain is also
>     available.
>     + * If the image sensor supports it, then the global analog Gain can
>     be controlled
>     + * by linear and exponential gain formula:
>     + *
>     + * \f$gain = analogLinearGainGlobal *
>     2^{analogExponentialGainGlobal} \f$
>     + * \todo not implemented in libipa
>     + */
>     +
>     +/**
>     + * \struct CameraSensorHelper::analogueGainConstants
>     + * \brief Analogue gain constants used for gain calculation
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::analogueGainConstants::type
>     + * \brief Analogue gain coding type
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::analogueGainConstants::m0
>     + * \brief Constant used in the analog Gain control coding/decoding.
>     + *
>     + * Note: either m0 or m1 shall be zero.
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::analogueGainConstants::c0
>     + * \brief Constant used in the analog Gain control coding/decoding.
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::analogueGainConstants::m1
>     + * \brief Constant used in the analog Gain control coding/decoding.
>     + *
>     + * Note: either m0 or m1 shall be zero.
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::analogueGainConstants::c1
>     + * \brief Constant used in the analog Gain control coding/decoding.
>     + */
>     +
>     +/**
>     + * \var CameraSensorHelper::analogueGain_
>     + * \brief The analogue gain parameters used for calculation
>     + *
>     + * The analogue gain is calculated through a formula, and its
>     parameters are
>     + * sensor specific. Use this variable to store the values at init time.
>     + *
>     + */
>     +
>     +/**
>     + * \class CameraSensorHelperFactory
>     + * \brief Registration of CameraSensorHelperFactory classes and
>     creation of instances
>     + *
>     + * To facilitate discovery and instantiation of CameraSensorHelper
>     classes, the
>     + * CameraSensorHelperFactory class maintains a registry of camera
>     sensor helper
>     + * classes. Each CameraSensorHelper subclass shall register itself
>     using the
>     + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create a
>     corresponding
>     + * instance of a CameraSensorHelperFactory subclass and register it
>     with the
>     + * static list of factories.
>     + */
>     +
>     +/**
>     + * \brief Construct a camera sensor helper factory
>     + * \param[in] name Name of the camera sensor helper class
>     + *
>     + * Creating an instance of the factory registers it with the global
>     list of
>     + * factories, accessible through the factories() function.
>     + *
>     + * The factory \a name is used for debug purpose and shall be unique.
>     + */
>     +
>     +CameraSensorHelperFactory::CameraSensorHelperFactory(const char *name)
>     +       : name_(name)
>     +{
>     +       registerType(this);
>     +}
>     +
>     +/**
>     + * \brief Create an instance of the CameraSensorHelper
>     corresponding to the factory
>     + *
>     + * \return A unique pointer to a new instance of the
>     CameraSensorHelper subclass
>     + * corresponding to the factory
>     + */
>     +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create()
>     +{
>     +       CameraSensorHelper *handler = createInstance();
>     +       return std::unique_ptr<CameraSensorHelper>(handler);
>     +}
>     +
>     +/**
>     + * \fn CameraSensorHelperFactory::name()
>     + * \brief Retrieve the factory name
>     + * \return The factory name
>     + */
>     +
>     +/**
>     + * \brief Add a camera sensor helper class to the registry
>     + * \param[in] factory Factory to use to construct the camera sensor
>     helper
>     + *
>     + * The caller is responsible to guarantee the uniqueness of the
>     camera sensor helper
>     + * name.
>     + */
>     +void
>     CameraSensorHelperFactory::registerType(CameraSensorHelperFactory
>     *factory)
>     +{
>     +       std::vector<CameraSensorHelperFactory *> &factories =
>     CameraSensorHelperFactory::factories();
>     +
>     +       factories.push_back(factory);
>     +}
>     +
>     +/**
>     + * \brief Retrieve the list of all camera sensor helper factories
>     + *
>     + * The static factories map is defined inside the function to
>     ensures it gets
>     + * initialized on first use, without any dependency on link order.
>     + *
>     + * \return The list of camera sensor helper factories
>     + */
>     +std::vector<CameraSensorHelperFactory *>
>     &CameraSensorHelperFactory::factories()
>     +{
>     +       static std::vector<CameraSensorHelperFactory *> factories;
>     +       return factories;
>     +}
>     +
>     +/**
>     + * \fn CameraSensorHelperFactory::createInstance()
>     + * \brief Create an instance of the CameraSensorHelper
>     corresponding to the factory
>     + *
>     + * This virtual function is implemented by the
>     REGISTER_CAMERA_SENSOR_HELPER()
>     + * macro. It creates a camera sensor helper instance associated
>     with the camera
>     + * sensor model.
>     + *
>     + * \return A pointer to a newly constructed instance of the
>     CameraSensorHelper
>     + * subclass corresponding to the factory
>     + */
>     +
>     +/**
>     + * \def REGISTER_CAMERA_SENSOR_HELPER
>     + * \brief Register a camera sensor helper with the camera sensor
>     helper factory
>     + * \param[in] name Sensor model name used to register the class
>     + * \param[in] handler Class name of CameraSensorHelper derived
>     class to register
>     + *
>     + * Register a CameraSensorHelper subclass with the factory and make
>     it available to
>     + * try and match devices.
>     + */
>     +
>     +/**
>     + * \class CameraSensorHelperImx219
>     + * \brief Create and give helpers for the imx219 sensor
>     + */
>     +
>     +/**
>     + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
>     + * \brief Construct a CameraSensorHelperImx219 instance for imx219
>     + * \param[in] name The sensor model name
>     + */
>     +class CameraSensorHelperImx219 : public CameraSensorHelper
>     +{
>     +public:
>     +       CameraSensorHelperImx219(const char *name);
>     +};
>     +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
>     +CameraSensorHelperImx219::CameraSensorHelperImx219(const char *name)
>     +       : CameraSensorHelper(name)
>     +{
>     +       analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
>     +}
>     +
>     +/**
>     + * \class CameraSensorHelperOv5670
>     + * \brief Create and give helpers for the ov5670 sensor
>     + */
>     +
>     +/**
>     + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
>     + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
>     + * \param[in] name The sensor model name
>     + */
>     +class CameraSensorHelperOv5670 : public CameraSensorHelper
>     +{
>     +public:
>     +       CameraSensorHelperOv5670(const char *name);
>     +};
>     +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
>     +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char *name)
>     +       : CameraSensorHelper(name)
>     +{
>     +       analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
>     +}
>     +
>     +/**
>     + * \class CameraSensorHelperOv5693
>     + * \brief Create and give helpers for the ov5693 sensor
>     + */
>     +
>     +/**
>     + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
>     + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
>     + * \param[in] name The sensor model name
>     + */
>     +class CameraSensorHelperOv5693 : public CameraSensorHelper
>     +{
>     +public:
>     +       CameraSensorHelperOv5693(const char *name);
>     +};
>     +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
>     +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char *name)
>     +       : CameraSensorHelper(name)
>     +{
>     +       analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
>     +}
>     +
>     +} /* namespace ipa */
>     +
>     +} /* namespace libcamera */
>     +
>     diff --git a/src/ipa/libipa/camera_sensor_helper.h
>     b/src/ipa/libipa/camera_sensor_helper.h
>     new file mode 100644
>     index 00000000..63031902
>     --- /dev/null
>     +++ b/src/ipa/libipa/camera_sensor_helper.h
>     @@ -0,0 +1,91 @@
>     +/* SPDX-License-Identifier: BSD-2-Clause */
>     +/*
>     + * Copyright (C) 2021 Ideas On Board
>     + *
>     + * camera_sensor_helper.h - helper class providing camera informations
>     + */
>     +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>     +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>     +
>     +#include <stdint.h>
>     +
>     +#include <string>
>     +
>     +#include <libcamera/class.h>
>     +#include <libcamera/object.h>
>     +
>     +namespace libcamera {
>     +
>     +namespace ipa {
>     +
>     +class CameraSensorHelper;
>     +
>     +class CameraSensorHelper : public Object
>     +{
>     +public:
>     +       CameraSensorHelper(const char *name);
>     +       virtual ~CameraSensorHelper();
>     +
>     +       const std::string &name() const { return name_; }
>     +       uint32_t getGainCode(double gain) const;
>     +       double getGain(uint32_t gainCode) const;
>     +
>     +protected:
>     +       enum AnalogueGainCapability : uint16_t {
>     +               GlobalGain = 0,
>     +               AlternateGlobalGain = 2,
>     +       };
>     +
>     +       struct analogueGainConstants {
>     +               uint16_t type;
>     +               int16_t m0;
>     +               int16_t c0;
>     +               int16_t m1;
>     +               int16_t c1;
>     +       };
>     +       analogueGainConstants analogueGain_;
>     +
>     +private:
>     +       std::string name_;
>     +       friend class CameraSensorHelperFactory;
>     +};
>     +
>     +class CameraSensorHelperFactory
>     +{
>     +public:
>     +       CameraSensorHelperFactory(const char *name);
>     +       virtual ~CameraSensorHelperFactory() = default;
>     +
>     +       std::unique_ptr<CameraSensorHelper> create();
>     +
>     +       const std::string &name() const { return name_; }
>     +
>     +       static void registerType(CameraSensorHelperFactory *factory);
>     +       static std::vector<CameraSensorHelperFactory *> &factories();
>     +
>     +private:
>     +       virtual CameraSensorHelper *createInstance() = 0;
>     +
>     +       std::string name_;
>     +};
>     +
>     +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)               
>             \
>     +       class handler##Factory final : public
>     CameraSensorHelperFactory     \
>     +       {                                                           
>            \
>     +       public:                                                     
>            \
>     +               handler##Factory() :
>     CameraSensorHelperFactory(#handler) {} \
>     +                                                                   
>             \
>     +       private:                                                   
>             \
>     +               CameraSensorHelper *createInstance()               
>             \
>     +               {                                                   
>            \
>     +                       return new handler(name);                   
>            \
>     +               }                                                   
>            \
>     +       };                                                         
>             \
>     +       static handler##Factory global_##handler##Factory;
>     +
>     +} /* namespace ipa */
>     +
>     +} /* namespace libcamera */
>     +
>     +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
>     +
>     diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
>     index 038fc490..dc90542c 100644
>     --- a/src/ipa/libipa/meson.build
>     +++ b/src/ipa/libipa/meson.build
>     @@ -2,11 +2,13 @@
> 
>      libipa_headers = files([
>          'algorithm.h',
>     +    'camera_sensor_helper.h',
>          'histogram.h'
>      ])
> 
>      libipa_sources = files([
>          'algorithm.cpp',
>     +    'camera_sensor_helper.cpp',
>          'histogram.cpp'
>      ])
> 
>     -- 
>     2.30.2
>

Naushir,

On 07/06/2021 20:15, Jean-Michel Hautbois wrote:
> Hi Naushir,
> 
> On 07/06/2021 19:31, Naushir Patuck wrote:
>> Hi Jean-Michel,
>>
>>
>>
>> On Mon, 7 Jun 2021 at 13:35, Jean-Michel Hautbois
>> <jeanmichel.hautbois@ideasonboard.com
>> <mailto:jeanmichel.hautbois@ideasonboard.com>> wrote:
>>
>>     Setting analogue gain for a specific sensor is not a straghtforward
>>     operation, as one needs to know how the gain is calculated for it.
>>
>>     This commit introduces a new camera sensor helper in libipa which aims
>>     to solve this specific issue.
>>     It is based on the MIPI alliance Specification for Camera Command Set
>>     and implements, for now, only the analogue "Global gain" mode.
>>
>>
>> I know this has probably been discussed in detail internally, but what
>> provisions
>> do you expect for gain formulas that do not conform to the CCI formula,
>> or  those
>> that are entirely table based?
> 
> It has not been discussed in detail no, and I am sure I have missed a
> lot of cases.
> For those specific cases, we may, for instance, have a new value in
> AnalogueGainCapability enum and let the subclass calculate the proper
> value ?
> I don't have this case right now in my hands, so it is difficult to know
> precisely what is the best way to do so ;-).
> 
>> Thanks,
>> Naush
>>
>>
>>     Is makes it possible to only have 4 parameters to store per sensor, and
>>     the gain calculation is then done identically for all of them. This
>>     commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
>>     ov5693.
>>
>>     Adding a new sensor is pretty straightfoward as one only needs to
>>     implement the sub-class for it and register that class to the
>>     CameraSensorHelperFactory.
>>
>>     Signed-off-by: Jean-Michel Hautbois
>>     <jeanmichel.hautbois@ideasonboard.com
>>     <mailto:jeanmichel.hautbois@ideasonboard.com>>
>>     ---
>>      src/ipa/libipa/camera_sensor_helper.cpp | 361 ++++++++++++++++++++++++
>>      src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
>>      src/ipa/libipa/meson.build              |   2 +
>>      3 files changed, 454 insertions(+)
>>      create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
>>      create mode 100644 src/ipa/libipa/camera_sensor_helper.h
>>
>>     diff --git a/src/ipa/libipa/camera_sensor_helper.cpp
>>     b/src/ipa/libipa/camera_sensor_helper.cpp
>>     new file mode 100644
>>     index 00000000..2bd82861
>>     --- /dev/null
>>     +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>>     @@ -0,0 +1,361 @@
>>     +/* SPDX-License-Identifier: BSD-2-Clause */
>>     +/*
>>     + * Copyright (C) 2021 Ideas On Board
>>     + *
>>     + * camera_sensor_helper.cpp - helper class providing camera
>>     informations
>>     + */
>>     +#include "camera_sensor_helper.h"
>>     +
>>     +#include <map>
>>     +
>>     +#include "libcamera/internal/log.h"
>>     +
>>     +/**
>>     + * \file camera_sensor_helper.h
>>     + * \brief Create helper class for each sensor
>>     + *
>>     + * Each camera sensor supported by libcamera may need specific
>>     informations to
>>     + * be sent (analogue gain is sensor dependant for instance).
>>     + *
>>     + * Every subclass of CameraSensorHelper shall be registered with
>>     libipa using
>>     + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
>>     + */
>>     +
>>     +namespace libcamera {
>>     +
>>     +LOG_DEFINE_CATEGORY(CameraSensorHelper)
>>     +
>>     +namespace ipa {
>>     +
>>     +/**
>>     + * \class CameraSensorHelper
>>     + * \brief Create and give helpers for each camera sensor in the
>>     pipeline
>>     + *
>>     + * CameraSensorHelper instances are unique and sensor dependant.
>>     + */
>>     +
>>     +/**
>>     + * \brief Construct a CameraSensorHelper instance
>>     + * \param[in] name The sensor model name
>>     + *
>>     + * The CameraSensorHelper instances shall never be constructed
>>     manually, but always
>>     + * through the CameraSensorHelperFactory::create() method
>>     implemented by the
>>     + * respective factories.
>>     + */
>>     +
>>     +CameraSensorHelper::CameraSensorHelper(const char *name)
>>     +       : name_(name)
>>     +{
>>     +       analogueGain_ = { GlobalGain, 1, 1, 0, 0 };
>>     +}
>>     +
>>     +CameraSensorHelper::~CameraSensorHelper()
>>     +{
>>     +}
>>     +
>>     +/**
>>     + * \fn CameraSensorHelper::getGainCode(double gain)
>>     + * \brief Get the analogue gain code to pass to V4L2 subdev control
>>     + * \param[in] gain The real gain to pass
>>     + *
>>     + * This function aims to abstract the calculation of the gain
>>     letting the IPA
>>     + * use the real gain for its estimations.
>>     + *
>>     + * The parameters come from the MIPI Alliance Camera Specification for
>>     + * Camera Command Set (CCS).
>>     + */
>>     +uint32_t CameraSensorHelper::getGainCode(double gain) const
>>     +{
>>     +       /* \todo we only support the global gain mode for now */
>>     +       if (analogueGain_.type != GlobalGain)
>>     +               return UINT32_MAX;
>>     +
>>     +       if (analogueGain_.m0 == 0)
>>     +               return (analogueGain_.c0 - gain * analogueGain_.c1)
>>     / (gain * analogueGain_.m1);
>>     +       if (analogueGain_.m1 == 0)
>>     +               return (gain * analogueGain_.c1 - analogueGain_.c0)
>>     / analogueGain_.m0;
>>     +
>>     +       LOG(CameraSensorHelper, Error) << "For any given image
>>     sensor either m0 or m1 shall be zero.";
>>     +       return 1;
>>     +}
>>     +
>>     +/**
>>     + * \fn CameraSensorHelper::getGain
>>     + * \brief Get the real gain from the V4l2 subdev control gain
>>     + * \param[in] gainCode The V4l2 subdev control gain
>>     + *
>>     + * This function aims to abstract the calculation of the gain
>>     letting the IPA
>>     + * use the real gain for its estimations. It is the counterpart of
>>     the function
>>     + * CameraSensorHelper::getGainCode.
>>     + *
>>     + * The parameters come from the MIPI Alliance Camera Specification for
>>     + * Camera Command Set (CCS).
>>     + */
>>     +double CameraSensorHelper::getGain(uint32_t gainCode) const
>>     +{
>>     +       if (analogueGain_.type != GlobalGain)
>>     +               return UINT32_MAX;
>>     +
>>     +       if (analogueGain_.m0 == 0)
>>     +               return analogueGain_.c0 / (analogueGain_.m1 *
>>     gainCode + analogueGain_.c1);
>>     +       if (analogueGain_.m1 == 0)
>>     +               return (analogueGain_.m0 * gainCode +
>>     analogueGain_.c0) / analogueGain_.c1;
>>     +
>>     +       LOG(CameraSensorHelper, Error) << "For any given image
>>     sensor either m0 or m1 shall be zero.";
>>     +       return 1.0;
>>     +}
>>     +
>>     +/**
>>     + * \fn CameraSensorHelper::name()
>>     + * \brief Retrieve the camera sensor helper name
>>     + * \return The camera sensor helper name
>>     + */
>>     +
>>     +/**
>>     + * \enum CameraSensorHelper::AnalogueGainCapability
>>     + * \brief Specify the Gain mode supported by the sensor
>>     + *
>>     + * Describes the image sensor analog Gain capabilities.
>>     + * Two modes are possible, depending on the sensor: Global and
>>     Alternate.
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::GlobalGain
>>     + * \brief Sensor supports Global gain
>>     + *
>>     + * The relationship between the integer Gain parameter and the
>>     resulting Gain
>>     + * multiplier is given by the following equation:
>>     + *
>>     + * \f$\frac{m0x+c0}{m1x+c1}\f$
>>     + *
>>     + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
>>     + * image-sensor-specific constants exposed by the sensor.
>>     + * These constants are static parameters, and for any given image
>>     sensor either
>>     + * m0 or m1 shall be zero.
>>     + *
>>     + * The full Gain equation therefore reduces to either:
>>     + *
>>     + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::AlternateGlobalGain
>>     + * \brief Sensor supports Analogue Global gain (introduced in CCS v1.1)
>>     + *
>>     + * Starting with CCS v1.1, Alternate Global Analog Gain is also
>>     available.
>>     + * If the image sensor supports it, then the global analog Gain can
>>     be controlled
>>     + * by linear and exponential gain formula:
>>     + *
>>     + * \f$gain = analogLinearGainGlobal *
>>     2^{analogExponentialGainGlobal} \f$
>>     + * \todo not implemented in libipa
>>     + */
>>     +
>>     +/**
>>     + * \struct CameraSensorHelper::analogueGainConstants
>>     + * \brief Analogue gain constants used for gain calculation
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::analogueGainConstants::type
>>     + * \brief Analogue gain coding type
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::analogueGainConstants::m0
>>     + * \brief Constant used in the analog Gain control coding/decoding.
>>     + *
>>     + * Note: either m0 or m1 shall be zero.
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::analogueGainConstants::c0
>>     + * \brief Constant used in the analog Gain control coding/decoding.
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::analogueGainConstants::m1
>>     + * \brief Constant used in the analog Gain control coding/decoding.
>>     + *
>>     + * Note: either m0 or m1 shall be zero.
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::analogueGainConstants::c1
>>     + * \brief Constant used in the analog Gain control coding/decoding.
>>     + */
>>     +
>>     +/**
>>     + * \var CameraSensorHelper::analogueGain_
>>     + * \brief The analogue gain parameters used for calculation
>>     + *
>>     + * The analogue gain is calculated through a formula, and its
>>     parameters are
>>     + * sensor specific. Use this variable to store the values at init time.
>>     + *
>>     + */
>>     +
>>     +/**
>>     + * \class CameraSensorHelperFactory
>>     + * \brief Registration of CameraSensorHelperFactory classes and
>>     creation of instances
>>     + *
>>     + * To facilitate discovery and instantiation of CameraSensorHelper
>>     classes, the
>>     + * CameraSensorHelperFactory class maintains a registry of camera
>>     sensor helper
>>     + * classes. Each CameraSensorHelper subclass shall register itself
>>     using the
>>     + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create a
>>     corresponding
>>     + * instance of a CameraSensorHelperFactory subclass and register it
>>     with the
>>     + * static list of factories.
>>     + */
>>     +
>>     +/**
>>     + * \brief Construct a camera sensor helper factory
>>     + * \param[in] name Name of the camera sensor helper class
>>     + *
>>     + * Creating an instance of the factory registers it with the global
>>     list of
>>     + * factories, accessible through the factories() function.
>>     + *
>>     + * The factory \a name is used for debug purpose and shall be unique.
>>     + */
>>     +
>>     +CameraSensorHelperFactory::CameraSensorHelperFactory(const char *name)
>>     +       : name_(name)
>>     +{
>>     +       registerType(this);
>>     +}
>>     +
>>     +/**
>>     + * \brief Create an instance of the CameraSensorHelper
>>     corresponding to the factory
>>     + *
>>     + * \return A unique pointer to a new instance of the
>>     CameraSensorHelper subclass
>>     + * corresponding to the factory
>>     + */
>>     +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create()
>>     +{
>>     +       CameraSensorHelper *handler = createInstance();
>>     +       return std::unique_ptr<CameraSensorHelper>(handler);
>>     +}
>>     +
>>     +/**
>>     + * \fn CameraSensorHelperFactory::name()
>>     + * \brief Retrieve the factory name
>>     + * \return The factory name
>>     + */
>>     +
>>     +/**
>>     + * \brief Add a camera sensor helper class to the registry
>>     + * \param[in] factory Factory to use to construct the camera sensor
>>     helper
>>     + *
>>     + * The caller is responsible to guarantee the uniqueness of the
>>     camera sensor helper
>>     + * name.
>>     + */
>>     +void
>>     CameraSensorHelperFactory::registerType(CameraSensorHelperFactory
>>     *factory)
>>     +{
>>     +       std::vector<CameraSensorHelperFactory *> &factories =
>>     CameraSensorHelperFactory::factories();
>>     +
>>     +       factories.push_back(factory);
>>     +}
>>     +
>>     +/**
>>     + * \brief Retrieve the list of all camera sensor helper factories
>>     + *
>>     + * The static factories map is defined inside the function to
>>     ensures it gets
>>     + * initialized on first use, without any dependency on link order.
>>     + *
>>     + * \return The list of camera sensor helper factories
>>     + */
>>     +std::vector<CameraSensorHelperFactory *>
>>     &CameraSensorHelperFactory::factories()
>>     +{
>>     +       static std::vector<CameraSensorHelperFactory *> factories;
>>     +       return factories;
>>     +}
>>     +
>>     +/**
>>     + * \fn CameraSensorHelperFactory::createInstance()
>>     + * \brief Create an instance of the CameraSensorHelper
>>     corresponding to the factory
>>     + *
>>     + * This virtual function is implemented by the
>>     REGISTER_CAMERA_SENSOR_HELPER()
>>     + * macro. It creates a camera sensor helper instance associated
>>     with the camera
>>     + * sensor model.
>>     + *
>>     + * \return A pointer to a newly constructed instance of the
>>     CameraSensorHelper
>>     + * subclass corresponding to the factory
>>     + */
>>     +
>>     +/**
>>     + * \def REGISTER_CAMERA_SENSOR_HELPER
>>     + * \brief Register a camera sensor helper with the camera sensor
>>     helper factory
>>     + * \param[in] name Sensor model name used to register the class
>>     + * \param[in] handler Class name of CameraSensorHelper derived
>>     class to register
>>     + *
>>     + * Register a CameraSensorHelper subclass with the factory and make
>>     it available to
>>     + * try and match devices.
>>     + */
>>     +
>>     +/**
>>     + * \class CameraSensorHelperImx219
>>     + * \brief Create and give helpers for the imx219 sensor
>>     + */
>>     +
>>     +/**
>>     + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
>>     + * \brief Construct a CameraSensorHelperImx219 instance for imx219
>>     + * \param[in] name The sensor model name
>>     + */
>>     +class CameraSensorHelperImx219 : public CameraSensorHelper
>>     +{
>>     +public:
>>     +       CameraSensorHelperImx219(const char *name);
>>     +};
>>     +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
>>     +CameraSensorHelperImx219::CameraSensorHelperImx219(const char *name)
>>     +       : CameraSensorHelper(name)
>>     +{
>>     +       analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
>>     +}
>>     +
>>     +/**
>>     + * \class CameraSensorHelperOv5670
>>     + * \brief Create and give helpers for the ov5670 sensor
>>     + */
>>     +
>>     +/**
>>     + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
>>     + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
>>     + * \param[in] name The sensor model name
>>     + */
>>     +class CameraSensorHelperOv5670 : public CameraSensorHelper
>>     +{
>>     +public:
>>     +       CameraSensorHelperOv5670(const char *name);
>>     +};
>>     +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
>>     +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char *name)
>>     +       : CameraSensorHelper(name)
>>     +{
>>     +       analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
>>     +}
>>     +
>>     +/**
>>     + * \class CameraSensorHelperOv5693
>>     + * \brief Create and give helpers for the ov5693 sensor
>>     + */
>>     +
>>     +/**
>>     + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
>>     + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
>>     + * \param[in] name The sensor model name
>>     + */
>>     +class CameraSensorHelperOv5693 : public CameraSensorHelper
>>     +{
>>     +public:
>>     +       CameraSensorHelperOv5693(const char *name);
>>     +};
>>     +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
>>     +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char *name)
>>     +       : CameraSensorHelper(name)
>>     +{
>>     +       analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
>>     +}
>>     +
>>     +} /* namespace ipa */
>>     +
>>     +} /* namespace libcamera */
>>     +
>>     diff --git a/src/ipa/libipa/camera_sensor_helper.h
>>     b/src/ipa/libipa/camera_sensor_helper.h
>>     new file mode 100644
>>     index 00000000..63031902
>>     --- /dev/null
>>     +++ b/src/ipa/libipa/camera_sensor_helper.h
>>     @@ -0,0 +1,91 @@
>>     +/* SPDX-License-Identifier: BSD-2-Clause */
>>     +/*
>>     + * Copyright (C) 2021 Ideas On Board
>>     + *
>>     + * camera_sensor_helper.h - helper class providing camera informations
>>     + */
>>     +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>>     +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>>     +
>>     +#include <stdint.h>
>>     +
>>     +#include <string>
>>     +
>>     +#include <libcamera/class.h>
>>     +#include <libcamera/object.h>
>>     +
>>     +namespace libcamera {
>>     +
>>     +namespace ipa {
>>     +
>>     +class CameraSensorHelper;
>>     +
>>     +class CameraSensorHelper : public Object
>>     +{
>>     +public:
>>     +       CameraSensorHelper(const char *name);
>>     +       virtual ~CameraSensorHelper();
>>     +
>>     +       const std::string &name() const { return name_; }
>>     +       uint32_t getGainCode(double gain) const;

Would you prefer getGainCode and getGain to be virtual, having a default
meyhod in CameraSensorHelper and letting those beeing overriden if a
specific sensor needs to have a different formula ?

>>     +       double getGain(uint32_t gainCode) const;
>>     +
>>     +protected:
>>     +       enum AnalogueGainCapability : uint16_t {
>>     +               GlobalGain = 0,
>>     +               AlternateGlobalGain = 2,
>>     +       };
>>     +
>>     +       struct analogueGainConstants {
>>     +               uint16_t type;
>>     +               int16_t m0;
>>     +               int16_t c0;
>>     +               int16_t m1;
>>     +               int16_t c1;
>>     +       };
>>     +       analogueGainConstants analogueGain_;
>>     +
>>     +private:
>>     +       std::string name_;
>>     +       friend class CameraSensorHelperFactory;
>>     +};
>>     +
>>     +class CameraSensorHelperFactory
>>     +{
>>     +public:
>>     +       CameraSensorHelperFactory(const char *name);
>>     +       virtual ~CameraSensorHelperFactory() = default;
>>     +
>>     +       std::unique_ptr<CameraSensorHelper> create();
>>     +
>>     +       const std::string &name() const { return name_; }
>>     +
>>     +       static void registerType(CameraSensorHelperFactory *factory);
>>     +       static std::vector<CameraSensorHelperFactory *> &factories();
>>     +
>>     +private:
>>     +       virtual CameraSensorHelper *createInstance() = 0;
>>     +
>>     +       std::string name_;
>>     +};
>>     +
>>     +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)               
>>             \
>>     +       class handler##Factory final : public
>>     CameraSensorHelperFactory     \
>>     +       {                                                           
>>            \
>>     +       public:                                                     
>>            \
>>     +               handler##Factory() :
>>     CameraSensorHelperFactory(#handler) {} \
>>     +                                                                   
>>             \
>>     +       private:                                                   
>>             \
>>     +               CameraSensorHelper *createInstance()               
>>             \
>>     +               {                                                   
>>            \
>>     +                       return new handler(name);                   
>>            \
>>     +               }                                                   
>>            \
>>     +       };                                                         
>>             \
>>     +       static handler##Factory global_##handler##Factory;
>>     +
>>     +} /* namespace ipa */
>>     +
>>     +} /* namespace libcamera */
>>     +
>>     +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
>>     +
>>     diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
>>     index 038fc490..dc90542c 100644
>>     --- a/src/ipa/libipa/meson.build
>>     +++ b/src/ipa/libipa/meson.build
>>     @@ -2,11 +2,13 @@
>>
>>      libipa_headers = files([
>>          'algorithm.h',
>>     +    'camera_sensor_helper.h',
>>          'histogram.h'
>>      ])
>>
>>      libipa_sources = files([
>>          'algorithm.cpp',
>>     +    'camera_sensor_helper.cpp',
>>          'histogram.cpp'
>>      ])
>>
>>     -- 
>>     2.30.2
>>

Hi Jean-Michel,


On Mon, 7 Jun 2021 at 20:35, Jean-Michel Hautbois <
jeanmichel.hautbois@ideasonboard.com> wrote:

> Naushir,
>
> On 07/06/2021 20:15, Jean-Michel Hautbois wrote:
> > Hi Naushir,
> >
> > On 07/06/2021 19:31, Naushir Patuck wrote:
> >> Hi Jean-Michel,
> >>
> >>
> >>
> >> On Mon, 7 Jun 2021 at 13:35, Jean-Michel Hautbois
> >> <jeanmichel.hautbois@ideasonboard.com
> >> <mailto:jeanmichel.hautbois@ideasonboard.com>> wrote:
> >>
> >>     Setting analogue gain for a specific sensor is not a straghtforward
> >>     operation, as one needs to know how the gain is calculated for it.
> >>
> >>     This commit introduces a new camera sensor helper in libipa which
> aims
> >>     to solve this specific issue.
> >>     It is based on the MIPI alliance Specification for Camera Command
> Set
> >>     and implements, for now, only the analogue "Global gain" mode.
> >>
> >>
> >> I know this has probably been discussed in detail internally, but what
> >> provisions
> >> do you expect for gain formulas that do not conform to the CCI formula,
> >> or  those
> >> that are entirely table based?
> >
> > It has not been discussed in detail no, and I am sure I have missed a
> > lot of cases.
> > For those specific cases, we may, for instance, have a new value in
> > AnalogueGainCapability enum and let the subclass calculate the proper
> > value ?
> > I don't have this case right now in my hands, so it is difficult to know
> > precisely what is the best way to do so ;-).
> >
> >> Thanks,
> >> Naush
> >>
> >>
> >>     Is makes it possible to only have 4 parameters to store per sensor,
> and
> >>     the gain calculation is then done identically for all of them. This
> >>     commit gives the gains for imx219 (based on RPi cam_helper), ov5670
> and
> >>     ov5693.
> >>
> >>     Adding a new sensor is pretty straightfoward as one only needs to
> >>     implement the sub-class for it and register that class to the
> >>     CameraSensorHelperFactory.
> >>
> >>     Signed-off-by: Jean-Michel Hautbois
> >>     <jeanmichel.hautbois@ideasonboard.com
> >>     <mailto:jeanmichel.hautbois@ideasonboard.com>>
> >>     ---
> >>      src/ipa/libipa/camera_sensor_helper.cpp | 361
> ++++++++++++++++++++++++
> >>      src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
> >>      src/ipa/libipa/meson.build              |   2 +
> >>      3 files changed, 454 insertions(+)
> >>      create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
> >>      create mode 100644 src/ipa/libipa/camera_sensor_helper.h
> >>
> >>     diff --git a/src/ipa/libipa/camera_sensor_helper.cpp
> >>     b/src/ipa/libipa/camera_sensor_helper.cpp
> >>     new file mode 100644
> >>     index 00000000..2bd82861
> >>     --- /dev/null
> >>     +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> >>     @@ -0,0 +1,361 @@
> >>     +/* SPDX-License-Identifier: BSD-2-Clause */
> >>     +/*
> >>     + * Copyright (C) 2021 Ideas On Board
> >>     + *
> >>     + * camera_sensor_helper.cpp - helper class providing camera
> >>     informations
> >>     + */
> >>     +#include "camera_sensor_helper.h"
> >>     +
> >>     +#include <map>
> >>     +
> >>     +#include "libcamera/internal/log.h"
> >>     +
> >>     +/**
> >>     + * \file camera_sensor_helper.h
> >>     + * \brief Create helper class for each sensor
> >>     + *
> >>     + * Each camera sensor supported by libcamera may need specific
> >>     informations to
> >>     + * be sent (analogue gain is sensor dependant for instance).
> >>     + *
> >>     + * Every subclass of CameraSensorHelper shall be registered with
> >>     libipa using
> >>     + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> >>     + */
> >>     +
> >>     +namespace libcamera {
> >>     +
> >>     +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> >>     +
> >>     +namespace ipa {
> >>     +
> >>     +/**
> >>     + * \class CameraSensorHelper
> >>     + * \brief Create and give helpers for each camera sensor in the
> >>     pipeline
> >>     + *
> >>     + * CameraSensorHelper instances are unique and sensor dependant.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \brief Construct a CameraSensorHelper instance
> >>     + * \param[in] name The sensor model name
> >>     + *
> >>     + * The CameraSensorHelper instances shall never be constructed
> >>     manually, but always
> >>     + * through the CameraSensorHelperFactory::create() method
> >>     implemented by the
> >>     + * respective factories.
> >>     + */
> >>     +
> >>     +CameraSensorHelper::CameraSensorHelper(const char *name)
> >>     +       : name_(name)
> >>     +{
> >>     +       analogueGain_ = { GlobalGain, 1, 1, 0, 0 };
> >>     +}
> >>     +
> >>     +CameraSensorHelper::~CameraSensorHelper()
> >>     +{
> >>     +}
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelper::getGainCode(double gain)
> >>     + * \brief Get the analogue gain code to pass to V4L2 subdev control
> >>     + * \param[in] gain The real gain to pass
> >>     + *
> >>     + * This function aims to abstract the calculation of the gain
> >>     letting the IPA
> >>     + * use the real gain for its estimations.
> >>     + *
> >>     + * The parameters come from the MIPI Alliance Camera Specification
> for
> >>     + * Camera Command Set (CCS).
> >>     + */
> >>     +uint32_t CameraSensorHelper::getGainCode(double gain) const
> >>     +{
> >>     +       /* \todo we only support the global gain mode for now */
> >>     +       if (analogueGain_.type != GlobalGain)
> >>     +               return UINT32_MAX;
> >>     +
> >>     +       if (analogueGain_.m0 == 0)
> >>     +               return (analogueGain_.c0 - gain * analogueGain_.c1)
> >>     / (gain * analogueGain_.m1);
> >>     +       if (analogueGain_.m1 == 0)
> >>     +               return (gain * analogueGain_.c1 - analogueGain_.c0)
> >>     / analogueGain_.m0;
> >>     +
> >>     +       LOG(CameraSensorHelper, Error) << "For any given image
> >>     sensor either m0 or m1 shall be zero.";
> >>     +       return 1;
> >>     +}
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelper::getGain
> >>     + * \brief Get the real gain from the V4l2 subdev control gain
> >>     + * \param[in] gainCode The V4l2 subdev control gain
> >>     + *
> >>     + * This function aims to abstract the calculation of the gain
> >>     letting the IPA
> >>     + * use the real gain for its estimations. It is the counterpart of
> >>     the function
> >>     + * CameraSensorHelper::getGainCode.
> >>     + *
> >>     + * The parameters come from the MIPI Alliance Camera Specification
> for
> >>     + * Camera Command Set (CCS).
> >>     + */
> >>     +double CameraSensorHelper::getGain(uint32_t gainCode) const
> >>     +{
> >>     +       if (analogueGain_.type != GlobalGain)
> >>     +               return UINT32_MAX;
> >>     +
> >>     +       if (analogueGain_.m0 == 0)
> >>     +               return analogueGain_.c0 / (analogueGain_.m1 *
> >>     gainCode + analogueGain_.c1);
> >>     +       if (analogueGain_.m1 == 0)
> >>     +               return (analogueGain_.m0 * gainCode +
> >>     analogueGain_.c0) / analogueGain_.c1;
> >>     +
> >>     +       LOG(CameraSensorHelper, Error) << "For any given image
> >>     sensor either m0 or m1 shall be zero.";
> >>     +       return 1.0;
> >>     +}
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelper::name()
> >>     + * \brief Retrieve the camera sensor helper name
> >>     + * \return The camera sensor helper name
> >>     + */
> >>     +
> >>     +/**
> >>     + * \enum CameraSensorHelper::AnalogueGainCapability
> >>     + * \brief Specify the Gain mode supported by the sensor
> >>     + *
> >>     + * Describes the image sensor analog Gain capabilities.
> >>     + * Two modes are possible, depending on the sensor: Global and
> >>     Alternate.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::GlobalGain
> >>     + * \brief Sensor supports Global gain
> >>     + *
> >>     + * The relationship between the integer Gain parameter and the
> >>     resulting Gain
> >>     + * multiplier is given by the following equation:
> >>     + *
> >>     + * \f$\frac{m0x+c0}{m1x+c1}\f$
> >>     + *
> >>     + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1
> are
> >>     + * image-sensor-specific constants exposed by the sensor.
> >>     + * These constants are static parameters, and for any given image
> >>     sensor either
> >>     + * m0 or m1 shall be zero.
> >>     + *
> >>     + * The full Gain equation therefore reduces to either:
> >>     + *
> >>     + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::AlternateGlobalGain
> >>     + * \brief Sensor supports Analogue Global gain (introduced in CCS
> v1.1)
> >>     + *
> >>     + * Starting with CCS v1.1, Alternate Global Analog Gain is also
> >>     available.
> >>     + * If the image sensor supports it, then the global analog Gain can
> >>     be controlled
> >>     + * by linear and exponential gain formula:
> >>     + *
> >>     + * \f$gain = analogLinearGainGlobal *
> >>     2^{analogExponentialGainGlobal} \f$
> >>     + * \todo not implemented in libipa
> >>     + */
> >>     +
> >>     +/**
> >>     + * \struct CameraSensorHelper::analogueGainConstants
> >>     + * \brief Analogue gain constants used for gain calculation
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::analogueGainConstants::type
> >>     + * \brief Analogue gain coding type
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::analogueGainConstants::m0
> >>     + * \brief Constant used in the analog Gain control coding/decoding.
> >>     + *
> >>     + * Note: either m0 or m1 shall be zero.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::analogueGainConstants::c0
> >>     + * \brief Constant used in the analog Gain control coding/decoding.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::analogueGainConstants::m1
> >>     + * \brief Constant used in the analog Gain control coding/decoding.
> >>     + *
> >>     + * Note: either m0 or m1 shall be zero.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::analogueGainConstants::c1
> >>     + * \brief Constant used in the analog Gain control coding/decoding.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \var CameraSensorHelper::analogueGain_
> >>     + * \brief The analogue gain parameters used for calculation
> >>     + *
> >>     + * The analogue gain is calculated through a formula, and its
> >>     parameters are
> >>     + * sensor specific. Use this variable to store the values at init
> time.
> >>     + *
> >>     + */
> >>     +
> >>     +/**
> >>     + * \class CameraSensorHelperFactory
> >>     + * \brief Registration of CameraSensorHelperFactory classes and
> >>     creation of instances
> >>     + *
> >>     + * To facilitate discovery and instantiation of CameraSensorHelper
> >>     classes, the
> >>     + * CameraSensorHelperFactory class maintains a registry of camera
> >>     sensor helper
> >>     + * classes. Each CameraSensorHelper subclass shall register itself
> >>     using the
> >>     + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create a
> >>     corresponding
> >>     + * instance of a CameraSensorHelperFactory subclass and register it
> >>     with the
> >>     + * static list of factories.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \brief Construct a camera sensor helper factory
> >>     + * \param[in] name Name of the camera sensor helper class
> >>     + *
> >>     + * Creating an instance of the factory registers it with the global
> >>     list of
> >>     + * factories, accessible through the factories() function.
> >>     + *
> >>     + * The factory \a name is used for debug purpose and shall be
> unique.
> >>     + */
> >>     +
> >>     +CameraSensorHelperFactory::CameraSensorHelperFactory(const char
> *name)
> >>     +       : name_(name)
> >>     +{
> >>     +       registerType(this);
> >>     +}
> >>     +
> >>     +/**
> >>     + * \brief Create an instance of the CameraSensorHelper
> >>     corresponding to the factory
> >>     + *
> >>     + * \return A unique pointer to a new instance of the
> >>     CameraSensorHelper subclass
> >>     + * corresponding to the factory
> >>     + */
> >>     +std::unique_ptr<CameraSensorHelper>
> CameraSensorHelperFactory::create()
> >>     +{
> >>     +       CameraSensorHelper *handler = createInstance();
> >>     +       return std::unique_ptr<CameraSensorHelper>(handler);
> >>     +}
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelperFactory::name()
> >>     + * \brief Retrieve the factory name
> >>     + * \return The factory name
> >>     + */
> >>     +
> >>     +/**
> >>     + * \brief Add a camera sensor helper class to the registry
> >>     + * \param[in] factory Factory to use to construct the camera sensor
> >>     helper
> >>     + *
> >>     + * The caller is responsible to guarantee the uniqueness of the
> >>     camera sensor helper
> >>     + * name.
> >>     + */
> >>     +void
> >>     CameraSensorHelperFactory::registerType(CameraSensorHelperFactory
> >>     *factory)
> >>     +{
> >>     +       std::vector<CameraSensorHelperFactory *> &factories =
> >>     CameraSensorHelperFactory::factories();
> >>     +
> >>     +       factories.push_back(factory);
> >>     +}
> >>     +
> >>     +/**
> >>     + * \brief Retrieve the list of all camera sensor helper factories
> >>     + *
> >>     + * The static factories map is defined inside the function to
> >>     ensures it gets
> >>     + * initialized on first use, without any dependency on link order.
> >>     + *
> >>     + * \return The list of camera sensor helper factories
> >>     + */
> >>     +std::vector<CameraSensorHelperFactory *>
> >>     &CameraSensorHelperFactory::factories()
> >>     +{
> >>     +       static std::vector<CameraSensorHelperFactory *> factories;
> >>     +       return factories;
> >>     +}
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelperFactory::createInstance()
> >>     + * \brief Create an instance of the CameraSensorHelper
> >>     corresponding to the factory
> >>     + *
> >>     + * This virtual function is implemented by the
> >>     REGISTER_CAMERA_SENSOR_HELPER()
> >>     + * macro. It creates a camera sensor helper instance associated
> >>     with the camera
> >>     + * sensor model.
> >>     + *
> >>     + * \return A pointer to a newly constructed instance of the
> >>     CameraSensorHelper
> >>     + * subclass corresponding to the factory
> >>     + */
> >>     +
> >>     +/**
> >>     + * \def REGISTER_CAMERA_SENSOR_HELPER
> >>     + * \brief Register a camera sensor helper with the camera sensor
> >>     helper factory
> >>     + * \param[in] name Sensor model name used to register the class
> >>     + * \param[in] handler Class name of CameraSensorHelper derived
> >>     class to register
> >>     + *
> >>     + * Register a CameraSensorHelper subclass with the factory and make
> >>     it available to
> >>     + * try and match devices.
> >>     + */
> >>     +
> >>     +/**
> >>     + * \class CameraSensorHelperImx219
> >>     + * \brief Create and give helpers for the imx219 sensor
> >>     + */
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
> >>     + * \brief Construct a CameraSensorHelperImx219 instance for imx219
> >>     + * \param[in] name The sensor model name
> >>     + */
> >>     +class CameraSensorHelperImx219 : public CameraSensorHelper
> >>     +{
> >>     +public:
> >>     +       CameraSensorHelperImx219(const char *name);
> >>     +};
> >>     +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> >>     +CameraSensorHelperImx219::CameraSensorHelperImx219(const char
> *name)
> >>     +       : CameraSensorHelper(name)
> >>     +{
> >>     +       analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
> >>     +}
> >>     +
> >>     +/**
> >>     + * \class CameraSensorHelperOv5670
> >>     + * \brief Create and give helpers for the ov5670 sensor
> >>     + */
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
> >>     + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
> >>     + * \param[in] name The sensor model name
> >>     + */
> >>     +class CameraSensorHelperOv5670 : public CameraSensorHelper
> >>     +{
> >>     +public:
> >>     +       CameraSensorHelperOv5670(const char *name);
> >>     +};
> >>     +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> >>     +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char
> *name)
> >>     +       : CameraSensorHelper(name)
> >>     +{
> >>     +       analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
> >>     +}
> >>     +
> >>     +/**
> >>     + * \class CameraSensorHelperOv5693
> >>     + * \brief Create and give helpers for the ov5693 sensor
> >>     + */
> >>     +
> >>     +/**
> >>     + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
> >>     + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
> >>     + * \param[in] name The sensor model name
> >>     + */
> >>     +class CameraSensorHelperOv5693 : public CameraSensorHelper
> >>     +{
> >>     +public:
> >>     +       CameraSensorHelperOv5693(const char *name);
> >>     +};
> >>     +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> >>     +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char
> *name)
> >>     +       : CameraSensorHelper(name)
> >>     +{
> >>     +       analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
> >>     +}
> >>     +
> >>     +} /* namespace ipa */
> >>     +
> >>     +} /* namespace libcamera */
> >>     +
> >>     diff --git a/src/ipa/libipa/camera_sensor_helper.h
> >>     b/src/ipa/libipa/camera_sensor_helper.h
> >>     new file mode 100644
> >>     index 00000000..63031902
> >>     --- /dev/null
> >>     +++ b/src/ipa/libipa/camera_sensor_helper.h
> >>     @@ -0,0 +1,91 @@
> >>     +/* SPDX-License-Identifier: BSD-2-Clause */
> >>     +/*
> >>     + * Copyright (C) 2021 Ideas On Board
> >>     + *
> >>     + * camera_sensor_helper.h - helper class providing camera
> informations
> >>     + */
> >>     +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> >>     +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> >>     +
> >>     +#include <stdint.h>
> >>     +
> >>     +#include <string>
> >>     +
> >>     +#include <libcamera/class.h>
> >>     +#include <libcamera/object.h>
> >>     +
> >>     +namespace libcamera {
> >>     +
> >>     +namespace ipa {
> >>     +
> >>     +class CameraSensorHelper;
> >>     +
> >>     +class CameraSensorHelper : public Object
> >>     +{
> >>     +public:
> >>     +       CameraSensorHelper(const char *name);
> >>     +       virtual ~CameraSensorHelper();
> >>     +
> >>     +       const std::string &name() const { return name_; }
> >>     +       uint32_t getGainCode(double gain) const;
>
> Would you prefer getGainCode and getGain to be virtual, having a default
> meyhod in CameraSensorHelper and letting those beeing overriden if a
> specific sensor needs to have a different formula ?
>

The Raspberry Pi CamHelper does keep these functions as virtual.  However,
I know Laurent and others would have a preference of using static data where
possible.  Perhaps just something to consider for the future rather than
doing
it now.

Regards,
Naush



>
> >>     +       double getGain(uint32_t gainCode) const;
> >>     +
> >>     +protected:
> >>     +       enum AnalogueGainCapability : uint16_t {
> >>     +               GlobalGain = 0,
> >>     +               AlternateGlobalGain = 2,
> >>     +       };
> >>     +
> >>     +       struct analogueGainConstants {
> >>     +               uint16_t type;
> >>     +               int16_t m0;
> >>     +               int16_t c0;
> >>     +               int16_t m1;
> >>     +               int16_t c1;
> >>     +       };
> >>     +       analogueGainConstants analogueGain_;
> >>     +
> >>     +private:
> >>     +       std::string name_;
> >>     +       friend class CameraSensorHelperFactory;
> >>     +};
> >>     +
> >>     +class CameraSensorHelperFactory
> >>     +{
> >>     +public:
> >>     +       CameraSensorHelperFactory(const char *name);
> >>     +       virtual ~CameraSensorHelperFactory() = default;
> >>     +
> >>     +       std::unique_ptr<CameraSensorHelper> create();
> >>     +
> >>     +       const std::string &name() const { return name_; }
> >>     +
> >>     +       static void registerType(CameraSensorHelperFactory
> *factory);
> >>     +       static std::vector<CameraSensorHelperFactory *>
> &factories();
> >>     +
> >>     +private:
> >>     +       virtual CameraSensorHelper *createInstance() = 0;
> >>     +
> >>     +       std::string name_;
> >>     +};
> >>     +
> >>     +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)
> >>             \
> >>     +       class handler##Factory final : public
> >>     CameraSensorHelperFactory     \
> >>     +       {
> >>            \
> >>     +       public:
> >>            \
> >>     +               handler##Factory() :
> >>     CameraSensorHelperFactory(#handler) {} \
> >>     +
> >>             \
> >>     +       private:
> >>             \
> >>     +               CameraSensorHelper *createInstance()
> >>             \
> >>     +               {
> >>            \
> >>     +                       return new handler(name);
> >>            \
> >>     +               }
> >>            \
> >>     +       };
> >>             \
> >>     +       static handler##Factory global_##handler##Factory;
> >>     +
> >>     +} /* namespace ipa */
> >>     +
> >>     +} /* namespace libcamera */
> >>     +
> >>     +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
> >>     +
> >>     diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> >>     index 038fc490..dc90542c 100644
> >>     --- a/src/ipa/libipa/meson.build
> >>     +++ b/src/ipa/libipa/meson.build
> >>     @@ -2,11 +2,13 @@
> >>
> >>      libipa_headers = files([
> >>          'algorithm.h',
> >>     +    'camera_sensor_helper.h',
> >>          'histogram.h'
> >>      ])
> >>
> >>      libipa_sources = files([
> >>          'algorithm.cpp',
> >>     +    'camera_sensor_helper.cpp',
> >>          'histogram.cpp'
> >>      ])
> >>
> >>     --
> >>     2.30.2
> >>
>

Hi Jean-Michel,

Thank you for the patch.

On Mon, Jun 07, 2021 at 02:35:32PM +0200, Jean-Michel Hautbois wrote:
> Setting analogue gain for a specific sensor is not a straghtforward
> operation, as one needs to know how the gain is calculated for it.
> 
> This commit introduces a new camera sensor helper in libipa which aims
> to solve this specific issue.
> It is based on the MIPI alliance Specification for Camera Command Set
> and implements, for now, only the analogue "Global gain" mode.
> 
> Is makes it possible to only have 4 parameters to store per sensor, and
> the gain calculation is then done identically for all of them. This
> commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
> ov5693.
> 
> Adding a new sensor is pretty straightfoward as one only needs to
> implement the sub-class for it and register that class to the
> CameraSensorHelperFactory.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 361 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 454 insertions(+)
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
>  create mode 100644 src/ipa/libipa/camera_sensor_helper.h
> 
> diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
> new file mode 100644
> index 00000000..2bd82861
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,361 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021 Ideas On Board
> + *
> + * camera_sensor_helper.cpp - helper class providing camera informations
> + */
> +#include "camera_sensor_helper.h"
> +
> +#include <map>
> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Create helper class for each sensor
> + *
> + * Each camera sensor supported by libcamera may need specific informations to
> + * be sent (analogue gain is sensor dependant for instance).
> + *
> + * Every subclass of CameraSensorHelper shall be registered with libipa using
> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> +
> +namespace ipa {
> +
> +/**
> + * \class CameraSensorHelper
> + * \brief Create and give helpers for each camera sensor in the pipeline
> + *
> + * CameraSensorHelper instances are unique and sensor dependant.
> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + * \param[in] name The sensor model name
> + *
> + * The CameraSensorHelper instances shall never be constructed manually, but always
> + * through the CameraSensorHelperFactory::create() method implemented by the
> + * respective factories.

The respective factories implement createInstance(), not create(). I'd
drop "by the respective factories".

> + */
> +
> +CameraSensorHelper::CameraSensorHelper(const char *name)
> +	: name_(name)
> +{
> +	analogueGain_ = { GlobalGain, 1, 1, 0, 0 };

No need for this, it's set by all the subclasses.

> +}
> +
> +CameraSensorHelper::~CameraSensorHelper()
> +{
> +}
> +
> +/**
> + * \fn CameraSensorHelper::getGainCode(double gain)
> + * \brief Get the analogue gain code to pass to V4L2 subdev control
> + * \param[in] gain The real gain to pass
> + *
> + * This function aims to abstract the calculation of the gain letting the IPA
> + * use the real gain for its estimations.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + */
> +uint32_t CameraSensorHelper::getGainCode(double gain) const
> +{
> +	/* \todo we only support the global gain mode for now */

Then let's drop AlternateGlobalGain for now. Or we can address the todo
item already, it should be easy.

> +	if (analogueGain_.type != GlobalGain)
> +		return UINT32_MAX;
> +
> +	if (analogueGain_.m0 == 0)
> +		return (analogueGain_.c0 - gain * analogueGain_.c1) / (gain * analogueGain_.m1);

		return (analogueGain_.c0 - gain * analogueGain_.c1) /
		       (gain * analogueGain_.m1);

> +	if (analogueGain_.m1 == 0)
> +		return (gain * analogueGain_.c1 - analogueGain_.c0) / analogueGain_.m0;

You can also write

	return (analogueGain_.c0 - analogueGain_.c1 * gain) /
	       (analogueGain_.m1 * gain - analogueGain_.m0);

> +
> +	LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";

Make this an assert. I'm tempted to pass the analogueGainConstants
pointer to the CameraSensorHelper constructor to assert there.

> +	return 1;
> +}
> +
> +/**
> + * \fn CameraSensorHelper::getGain
> + * \brief Get the real gain from the V4l2 subdev control gain
> + * \param[in] gainCode The V4l2 subdev control gain
> + *
> + * This function aims to abstract the calculation of the gain letting the IPA
> + * use the real gain for its estimations. It is the counterpart of the function
> + * CameraSensorHelper::getGainCode.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + */
> +double CameraSensorHelper::getGain(uint32_t gainCode) const
> +{
> +	if (analogueGain_.type != GlobalGain)
> +		return UINT32_MAX;

That's not a double.

> +
> +	if (analogueGain_.m0 == 0)
> +		return analogueGain_.c0 / (analogueGain_.m1 * gainCode + analogueGain_.c1);
> +	if (analogueGain_.m1 == 0)
> +		return (analogueGain_.m0 * gainCode + analogueGain_.c0) / analogueGain_.c1;

You can also write

	return (analogueGain_.m0 * gainCode + analogueGain_.c0) /
	       (analogueGain_.m1 * gainCode + analogueGain_.c1)

> +
> +	LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";
> +	return 1.0;
> +}
> +
> +/**
> + * \fn CameraSensorHelper::name()
> + * \brief Retrieve the camera sensor helper name
> + * \return The camera sensor helper name
> + */
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainCapability

That's not a very descriptive name, I'd propose AnalogueGainType (or
AnalogueGainModel).

> + * \brief Specify the Gain mode supported by the sensor
> + *
> + * Describes the image sensor analog Gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::GlobalGain
> + * \brief Sensor supports Global gain

This is also not very descriptive, I'd propose AnalogueGainLinear (and
AnalogueGainExponential for AlternateGlobalGain).

> + *
> + * The relationship between the integer Gain parameter and the resulting Gain
> + * multiplier is given by the following equation:
> + *
> + * \f$\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants exposed by the sensor.
> + * These constants are static parameters, and for any given image sensor either
> + * m0 or m1 shall be zero.
> + *
> + * The full Gain equation therefore reduces to either:
> + *
> + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$

 * \f$fain = \frac...

> + */
> +
> +/**
> + * \var CameraSensorHelper::AlternateGlobalGain
> + * \brief Sensor supports Analogue Global gain (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analog Gain is also available.
> + * If the image sensor supports it, then the global analog Gain can be controlled
> + * by linear and exponential gain formula:
> + *
> + * \f$gain = analogLinearGainGlobal * 2^{analogExponentialGainGlobal} \f$
> + * \todo not implemented in libipa
> + */
> +
> +/**
> + * \struct CameraSensorHelper::analogueGainConstants
> + * \brief Analogue gain constants used for gain calculation
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::type
> + * \brief Analogue gain coding type
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::m0
> + * \brief Constant used in the analog Gain control coding/decoding.
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::c0
> + * \brief Constant used in the analog Gain control coding/decoding.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::m1
> + * \brief Constant used in the analog Gain control coding/decoding.
> + *
> + * Note: either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants::c1
> + * \brief Constant used in the analog Gain control coding/decoding.
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGain_
> + * \brief The analogue gain parameters used for calculation
> + *
> + * The analogue gain is calculated through a formula, and its parameters are
> + * sensor specific. Use this variable to store the values at init time.
> + *
> + */
> +
> +/**
> + * \class CameraSensorHelperFactory
> + * \brief Registration of CameraSensorHelperFactory classes and creation of instances
> + *
> + * To facilitate discovery and instantiation of CameraSensorHelper classes, the
> + * CameraSensorHelperFactory class maintains a registry of camera sensor helper
> + * classes. Each CameraSensorHelper subclass shall register itself using the
> + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create a corresponding
> + * instance of a CameraSensorHelperFactory subclass and register it with the
> + * static list of factories.
> + */
> +
> +/**
> + * \brief Construct a camera sensor helper factory
> + * \param[in] name Name of the camera sensor helper class
> + *
> + * Creating an instance of the factory registers it with the global list of
> + * factories, accessible through the factories() function.
> + *
> + * The factory \a name is used for debug purpose and shall be unique.
> + */
> +
> +CameraSensorHelperFactory::CameraSensorHelperFactory(const char *name)
> +	: name_(name)
> +{
> +	registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
> + *
> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
> + * corresponding to the factory
> + */
> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create()
> +{
> +	CameraSensorHelper *handler = createInstance();
> +	return std::unique_ptr<CameraSensorHelper>(handler);

There's no handler. s/handler/helper/ (or any other better name you can
think of). Same below.

> +}
> +
> +/**
> + * \fn CameraSensorHelperFactory::name()
> + * \brief Retrieve the factory name
> + * \return The factory name
> + */
> +
> +/**
> + * \brief Add a camera sensor helper class to the registry
> + * \param[in] factory Factory to use to construct the camera sensor helper
> + *
> + * The caller is responsible to guarantee the uniqueness of the camera sensor helper
> + * name.
> + */
> +void CameraSensorHelperFactory::registerType(CameraSensorHelperFactory *factory)
> +{
> +	std::vector<CameraSensorHelperFactory *> &factories = CameraSensorHelperFactory::factories();
> +
> +	factories.push_back(factory);
> +}
> +
> +/**
> + * \brief Retrieve the list of all camera sensor helper factories
> + *
> + * The static factories map is defined inside the function to ensures it gets
> + * initialized on first use, without any dependency on link order.
> + *
> + * \return The list of camera sensor helper factories
> + */
> +std::vector<CameraSensorHelperFactory *> &CameraSensorHelperFactory::factories()
> +{
> +	static std::vector<CameraSensorHelperFactory *> factories;
> +	return factories;
> +}
> +
> +/**
> + * \fn CameraSensorHelperFactory::createInstance()
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
> + *
> + * This virtual function is implemented by the REGISTER_CAMERA_SENSOR_HELPER()
> + * macro. It creates a camera sensor helper instance associated with the camera
> + * sensor model.
> + *
> + * \return A pointer to a newly constructed instance of the CameraSensorHelper
> + * subclass corresponding to the factory
> + */
> +
> +/**
> + * \def REGISTER_CAMERA_SENSOR_HELPER
> + * \brief Register a camera sensor helper with the camera sensor helper factory
> + * \param[in] name Sensor model name used to register the class
> + * \param[in] handler Class name of CameraSensorHelper derived class to register
> + *
> + * Register a CameraSensorHelper subclass with the factory and make it available to
> + * try and match devices.
> + */
> +
> +/**
> + * \class CameraSensorHelperImx219
> + * \brief Create and give helpers for the imx219 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
> + * \brief Construct a CameraSensorHelperImx219 instance for imx219
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperImx219(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> +CameraSensorHelperImx219::CameraSensorHelperImx219(const char *name)
> +	: CameraSensorHelper(name)
> +{
> +	analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
> +}
> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
> + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5670(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char *name)
> +	: CameraSensorHelper(name)
> +{
> +	analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
> +}
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +
> +/**
> + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
> + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
> + * \param[in] name The sensor model name
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5693(const char *name);
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char *name)
> +	: CameraSensorHelper(name)
> +{
> +	analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
> +}
> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> +
> diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
> new file mode 100644
> index 00000000..63031902
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: BSD-2-Clause */
> +/*
> + * Copyright (C) 2021 Ideas On Board
> + *
> + * camera_sensor_helper.h - helper class providing camera informations
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <string>
> +
> +#include <libcamera/class.h>

This doesn't seem to be used, but it should, the CameraSensorHelper and
CameraSensorHelperFactory classes should not be copyable or moveable.

> +#include <libcamera/object.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper;
> +
> +class CameraSensorHelper : public Object

Any reason this class inherits from Object ?

> +{
> +public:
> +	CameraSensorHelper(const char *name);
> +	virtual ~CameraSensorHelper();
> +
> +	const std::string &name() const { return name_; }

This doesn't seem to be used.

> +	uint32_t getGainCode(double gain) const;
> +	double getGain(uint32_t gainCode) const;

We don't usually use a "get" prefix, should these be called gainCode()
and gain() ?

> +
> +protected:
> +	enum AnalogueGainCapability : uint16_t {

Is there a need to specify the underlying data type explicitly ?

> +		GlobalGain = 0,
> +		AlternateGlobalGain = 2,
> +	};
> +
> +	struct analogueGainConstants {

s/analogueGainConstants/AnalogueGainConstants/

> +		uint16_t type;
> +		int16_t m0;
> +		int16_t c0;
> +		int16_t m1;
> +		int16_t c1;
> +	};
> +	analogueGainConstants analogueGain_;

The variable name can be mistaken to mean it stores a gain, while it
stores the constants.

It would be nice to make this const.

> +
> +private:
> +	std::string name_;
> +	friend class CameraSensorHelperFactory;
> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +	CameraSensorHelperFactory(const char *name);
> +	virtual ~CameraSensorHelperFactory() = default;
> +
> +	std::unique_ptr<CameraSensorHelper> create();
> +
> +	const std::string &name() const { return name_; }

This doesn't seem to be used.

> +
> +	static void registerType(CameraSensorHelperFactory *factory);
> +	static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +private:
> +	virtual CameraSensorHelper *createInstance() = 0;
> +
> +	std::string name_;
> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)                        \
> +	class handler##Factory final : public CameraSensorHelperFactory     \
> +	{                                                                   \
> +	public:                                                             \
> +		handler##Factory() : CameraSensorHelperFactory(#handler) {} \
> +                                                                            \
> +	private:                                                            \
> +		CameraSensorHelper *createInstance()                        \
> +		{                                                           \
> +			return new handler(name);                           \
> +		}                                                           \
> +	};                                                                  \
> +	static handler##Factory global_##handler##Factory;

You can drop one indentation level (I know checkstyle.py complains).

> +
> +} /* namespace ipa */
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
> +
> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> index 038fc490..dc90542c 100644
> --- a/src/ipa/libipa/meson.build
> +++ b/src/ipa/libipa/meson.build
> @@ -2,11 +2,13 @@
>  
>  libipa_headers = files([
>      'algorithm.h',
> +    'camera_sensor_helper.h',
>      'histogram.h'
>  ])
>  
>  libipa_sources = files([
>      'algorithm.cpp',
> +    'camera_sensor_helper.cpp',
>      'histogram.cpp'
>  ])
>

Hi Jacopo,

On Mon, Jun 07, 2021 at 06:05:33PM +0200, Jacopo Mondi wrote:
> On Mon, Jun 07, 2021 at 02:35:32PM +0200, Jean-Michel Hautbois wrote:
> > Setting analogue gain for a specific sensor is not a straghtforward
> > operation, as one needs to know how the gain is calculated for it.
> 
> Please bear with my poor understanding of the issue, but looking at
> the code it doesn't seem the different is in how the gain is
> calculated but rather in which constant parameters are used.

That's partly true (and one could argue that the parameters are part of
the calculation, but that's more of a semantics discussion). There are
sensors that implement a gain model which can't be covered by the
formulas in this patch. We expect more work in this area when we'll have
to support such sensors.

> > This commit introduces a new camera sensor helper in libipa which aims
> > to solve this specific issue.
> > It is based on the MIPI alliance Specification for Camera Command Set
> > and implements, for now, only the analogue "Global gain" mode.
> 
> I should first go through this document, so I'll probably have only
> drive-by comments and nits here and there
> 
> > Is makes it possible to only have 4 parameters to store per sensor, and
> > the gain calculation is then done identically for all of them. This
> > commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
> > ov5693.
> >
> > Adding a new sensor is pretty straightfoward as one only needs to
> > implement the sub-class for it and register that class to the
> > CameraSensorHelperFactory.
> 
> As asked offline, the current fatory implementation is the same as the
> one we have for pipeline handlers, which requires static
> initialization to make sure they are registered at library
> initialization time. I suspect without this requirement the factory
> here could be made simpler, but that's minor...
> 
> > Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
> > ---
> >  src/ipa/libipa/camera_sensor_helper.cpp | 361 ++++++++++++++++++++++++
> >  src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
> >  src/ipa/libipa/meson.build              |   2 +
> >  3 files changed, 454 insertions(+)
> >  create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
> >  create mode 100644 src/ipa/libipa/camera_sensor_helper.h
> >
> > diff --git a/src/ipa/libipa/camera_sensor_helper.cpp b/src/ipa/libipa/camera_sensor_helper.cpp
> > new file mode 100644
> > index 00000000..2bd82861
> > --- /dev/null
> > +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> > @@ -0,0 +1,361 @@
> > +/* SPDX-License-Identifier: BSD-2-Clause */
> > +/*
> > + * Copyright (C) 2021 Ideas On Board
> > + *
> > + * camera_sensor_helper.cpp - helper class providing camera informations
> 
> Nit: 'Helper'
> as I've received the same comment multiple times, 'information' is
> uncountable, so no plural
> 
> > + */
> > +#include "camera_sensor_helper.h"
> > +
> > +#include <map>
> > +
> > +#include "libcamera/internal/log.h"
> > +
> > +/**
> > + * \file camera_sensor_helper.h
> > + * \brief Create helper class for each sensor
> > + *
> > + * Each camera sensor supported by libcamera may need specific informations to
> > + * be sent (analogue gain is sensor dependant for instance).
> > + *
> > + * Every subclass of CameraSensorHelper shall be registered with libipa using
> > + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> > + */
> > +
> > +namespace libcamera {
> > +
> > +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> > +
> > +namespace ipa {
> > +
> > +/**
> > + * \class CameraSensorHelper
> > + * \brief Create and give helpers for each camera sensor in the pipeline
> 
> I would here and maybe above in the file description drop the 'create
> and give' part. The CameraSensorHelper base class computes sensor
> tuning parameters using sensor-specific constants. The factory instead
> does the actual object creation
> 
> > + *
>  sensor-specific constants. The factory instead does the actual object
>  creation
> 
> > + * CameraSensorHelper instances are unique and sensor dependant.
> 
> Is the base class meant to be used as a default if not sensor-specific
> sub-class is registered ?
> 
> > + */
> > +
> > +/**
> > + * \brief Construct a CameraSensorHelper instance
> > + * \param[in] name The sensor model name
> > + *
> > + * The CameraSensorHelper instances shall never be constructed manually, but always
> > + * through the CameraSensorHelperFactory::create() method implemented by the
> > + * respective factories.
> > + */
> > +
> 
> Empty line
> 
> > +CameraSensorHelper::CameraSensorHelper(const char *name)
> > +	: name_(name)
> > +{
> > +	analogueGain_ = { GlobalGain, 1, 1, 0, 0 };
> > +}
> 
> I wonder, we don't support AlternateGlobalGain at the moment, do you
> expect it to be required soon ?
> 
> > +
> > +CameraSensorHelper::~CameraSensorHelper()
> > +{
> > +}
> > +
> > +/**
> > + * \fn CameraSensorHelper::getGainCode(double gain)
> 
> If you document the function just defined below, you don't need the
> \fn anchor
> 
> Library-wide we don't use 'get' for getters, so this might just be
> gainCode() ?
> 
> > + * \brief Get the analogue gain code to pass to V4L2 subdev control
> 
> Aren't we computing the gain code from the analogue gain value ?
> 
> > + * \param[in] gain The real gain to pass
> > + *
> > + * This function aims to abstract the calculation of the gain letting the IPA
> > + * use the real gain for its estimations.
> > + *
> > + * The parameters come from the MIPI Alliance Camera Specification for
> > + * Camera Command Set (CCS).
> 
> Do you mean the m0, c0, etc etc paramteres ? Maybe this is better
> specified in the enum documentation ?
> 
> > + */
> > +uint32_t CameraSensorHelper::getGainCode(double gain) const
> > +{
> > +	/* \todo we only support the global gain mode for now */
> > +	if (analogueGain_.type != GlobalGain)
> > +		return UINT32_MAX;
> > +
> > +	if (analogueGain_.m0 == 0)
> > +		return (analogueGain_.c0 - gain * analogueGain_.c1) / (gain * analogueGain_.m1);
> > +	if (analogueGain_.m1 == 0)
> > +	return (gain * analogueGain_.c1 - analogueGain_.c0) / analogueGain_.m0;
> 
> You can break the two lines
> 
> > +
> > +	LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";
> > +	return 1;
> 
> Aren't the two error conditions verified by assertions ? Otherwise we
> return two different error codes (MAXINT and 1) which are difficult to
> identify.
> 
> > +}
> > +
> > +/**
> > + * \fn CameraSensorHelper::getGain
> > + * \brief Get the real gain from the V4l2 subdev control gain
> > + * \param[in] gainCode The V4l2 subdev control gain
> > + *
> > + * This function aims to abstract the calculation of the gain letting the IPA
> > + * use the real gain for its estimations. It is the counterpart of the function
> > + * CameraSensorHelper::getGainCode.
> > + *
> > + * The parameters come from the MIPI Alliance Camera Specification for
> > + * Camera Command Set (CCS).
> 
> Same comments as above
> 
> > + */
> > +double CameraSensorHelper::getGain(uint32_t gainCode) const
> > +{
> > +	if (analogueGain_.type != GlobalGain)
> > +		return UINT32_MAX;
> > +
> > +	if (analogueGain_.m0 == 0)
> > +		return analogueGain_.c0 / (analogueGain_.m1 * gainCode + analogueGain_.c1);
> > +	if (analogueGain_.m1 == 0)
> > +		return (analogueGain_.m0 * gainCode + analogueGain_.c0) / analogueGain_.c1;
> > +
> > +	LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";
> > +	return 1.0;
> > +}
> 
> ditto
> 
> Also, these smells like static functions as they only use class
> members constants for computations and do not hold any state. This
> however does not play well with the class hierarchy...
> 
> > +
> > +/**
> > + * \fn CameraSensorHelper::name()
> > + * \brief Retrieve the camera sensor helper name
> > + * \return The camera sensor helper name
> > + */
> > +
> > +/**
> > + * \enum CameraSensorHelper::AnalogueGainCapability
> > + * \brief Specify the Gain mode supported by the sensor
> > + *
> > + * Describes the image sensor analog Gain capabilities.
> > + * Two modes are possible, depending on the sensor: Global and Alternate.
> > + */
> > +
> > +/**
> > + * \var CameraSensorHelper::GlobalGain
> > + * \brief Sensor supports Global gain
> > + *
> > + * The relationship between the integer Gain parameter and the resulting Gain
> > + * multiplier is given by the following equation:
> > + *
> > + * \f$\frac{m0x+c0}{m1x+c1}\f$
> > + *
> > + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> > + * image-sensor-specific constants exposed by the sensor.
> > + * These constants are static parameters, and for any given image sensor either
> > + * m0 or m1 shall be zero.
> > + *
> > + * The full Gain equation therefore reduces to either:
> > + *
> > + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> > + */
> > +
> > +/**
> > + * \var CameraSensorHelper::AlternateGlobalGain
> > + * \brief Sensor supports Analogue Global gain (introduced in CCS v1.1)
> > + *
> > + * Starting with CCS v1.1, Alternate Global Analog Gain is also available.
> > + * If the image sensor supports it, then the global analog Gain can be controlled
> > + * by linear and exponential gain formula:
> > + *
> > + * \f$gain = analogLinearGainGlobal * 2^{analogExponentialGainGlobal} \f$
> > + * \todo not implemented in libipa
> > + */
> > +
> > +/**
> > + * \struct CameraSensorHelper::analogueGainConstants
> > + * \brief Analogue gain constants used for gain calculation
> > + */
> 
> How do you envision this class to evolve ? I mean, it will go beyoind
> just analogue gain calculations ? As otherwise a single class with a
> map of sensor specific gain constants would do...
> 
> > +
> > +/**
> > + * \var CameraSensorHelper::analogueGainConstants::type
> > + * \brief Analogue gain coding type
> > + */
> > +
> > +/**
> > + * \var CameraSensorHelper::analogueGainConstants::m0
> > + * \brief Constant used in the analog Gain control coding/decoding.
> > + *
> > + * Note: either m0 or m1 shall be zero.
> > + */
> > +
> > +/**
> > + * \var CameraSensorHelper::analogueGainConstants::c0
> > + * \brief Constant used in the analog Gain control coding/decoding.
> > + */
> > +
> > +/**
> > + * \var CameraSensorHelper::analogueGainConstants::m1
> > + * \brief Constant used in the analog Gain control coding/decoding.
> 
> Nit: briefs do not end with '.'
> 
> > + *
> > + * Note: either m0 or m1 shall be zero.
> > + */
> > +
> > +/**
> > + * \var CameraSensorHelper::analogueGainConstants::c1
> > + * \brief Constant used in the analog Gain control coding/decoding.
> 
> I presume I have to read the CCS specs to know what this parameters
> actually are :)
> 
> > + */
> > +
> > +/**
> > + * \var CameraSensorHelper::analogueGain_
> 
> Maybe something in the name that makes it clear these are params ?
> Analouge gain to me is what 'getGain()' calculates, am I mistaken ?
> 
> > + * \brief The analogue gain parameters used for calculation
> > + *
> > + * The analogue gain is calculated through a formula, and its parameters are
> > + * sensor specific. Use this variable to store the values at init time.
> > + *
> 
> Empty line
> 
> > + */
> > +
> 
> I'll skip the factory review for now
> 
> > +/**
> 
> [snip]
> 
> > +
> > +/**
> > + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
> > + * \brief Construct a CameraSensorHelperImx219 instance for imx219
> > + * \param[in] name The sensor model name
> > + */

No need to document each subclass.

> > +class CameraSensorHelperImx219 : public CameraSensorHelper
> > +{
> > +public:
> > +	CameraSensorHelperImx219(const char *name);
> > +};
> > +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> 
> I would add an empty line here and make it look like
> 
> class CameraSensorHelperXYZ : public CameraSensorHelper
> {
> public:
> 	CameraSensorHelperXYZ(const char *name)
>         {
>                 ...
>         }
> };

Agreed, an inline constructor seems better.

> REGISTER_CAMERA_SENSOR_HELPER("XYZ", CameraSensorHelperXYZ)
> 
> 
> > +CameraSensorHelperImx219::CameraSensorHelperImx219(const char *name)
> > +	: CameraSensorHelper(name)
> > +{
> > +	analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
> > +}
> > +
> > +/**
> > + * \class CameraSensorHelperOv5670
> > + * \brief Create and give helpers for the ov5670 sensor
> > + */
> > +
> > +/**
> > + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
> > + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
> > + * \param[in] name The sensor model name
> > + */
> > +class CameraSensorHelperOv5670 : public CameraSensorHelper
> > +{
> > +public:
> > +	CameraSensorHelperOv5670(const char *name);
> > +};
> > +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> > +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char *name)
> > +	: CameraSensorHelper(name)
> > +{
> > +	analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
> > +}
> > +
> > +/**
> > + * \class CameraSensorHelperOv5693
> > + * \brief Create and give helpers for the ov5693 sensor
> > + */
> > +
> > +/**
> > + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
> > + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
> > + * \param[in] name The sensor model name
> > + */
> > +class CameraSensorHelperOv5693 : public CameraSensorHelper
> > +{
> > +public:
> > +	CameraSensorHelperOv5693(const char *name);
> > +};
> > +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> > +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char *name)
> > +	: CameraSensorHelper(name)
> > +{
> > +	analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
> > +}
> > +
> > +} /* namespace ipa */
> > +
> > +} /* namespace libcamera */
> > +
> > diff --git a/src/ipa/libipa/camera_sensor_helper.h b/src/ipa/libipa/camera_sensor_helper.h
> > new file mode 100644
> > index 00000000..63031902
> > --- /dev/null
> > +++ b/src/ipa/libipa/camera_sensor_helper.h
> > @@ -0,0 +1,91 @@
> > +/* SPDX-License-Identifier: BSD-2-Clause */
> > +/*
> > + * Copyright (C) 2021 Ideas On Board
> > + *
> > + * camera_sensor_helper.h - helper class providing camera informations
> > + */
> > +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> > +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> > +
> > +#include <stdint.h>
> > +
> > +#include <string>
> > +
> > +#include <libcamera/class.h>
> > +#include <libcamera/object.h>
> > +
> > +namespace libcamera {
> > +
> > +namespace ipa {
> > +
> > +class CameraSensorHelper;
> > +
> > +class CameraSensorHelper : public Object
> > +{
> > +public:
> > +	CameraSensorHelper(const char *name);
> > +	virtual ~CameraSensorHelper();
> > +
> > +	const std::string &name() const { return name_; }
> > +	uint32_t getGainCode(double gain) const;
> > +	double getGain(uint32_t gainCode) const;
> > +
> > +protected:
> > +	enum AnalogueGainCapability : uint16_t {
> > +		GlobalGain = 0,
> > +		AlternateGlobalGain = 2,
> 
> Are the gain type values defined by the CCS specs ?
> 
> > +	};
> > +
> > +	struct analogueGainConstants {
> > +		uint16_t type;
> > +		int16_t m0;
> > +		int16_t c0;
> > +		int16_t m1;
> > +		int16_t c1;
> > +	};
> > +	analogueGainConstants analogueGain_;
> > +
> > +private:
> > +	std::string name_;
> > +	friend class CameraSensorHelperFactory;
> 
> Do you need this friend class declaration ?
> The constructor is public...

Doesn't seem needed indeed.

> > +};
> > +
> > +class CameraSensorHelperFactory
> > +{
> > +public:
> > +	CameraSensorHelperFactory(const char *name);
> > +	virtual ~CameraSensorHelperFactory() = default;
> > +
> > +	std::unique_ptr<CameraSensorHelper> create();
> > +
> > +	const std::string &name() const { return name_; }
> > +
> > +	static void registerType(CameraSensorHelperFactory *factory);
> > +	static std::vector<CameraSensorHelperFactory *> &factories();
> > +
> > +private:
> > +	virtual CameraSensorHelper *createInstance() = 0;
> > +
> > +	std::string name_;
> > +};
> > +
> > +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)                        \
> > +	class handler##Factory final : public CameraSensorHelperFactory     \
> > +	{                                                                   \
> > +	public:                                                             \
> > +		handler##Factory() : CameraSensorHelperFactory(#handler) {} \
> > +                                                                            \
> > +	private:                                                            \
> > +		CameraSensorHelper *createInstance()                        \
> > +		{                                                           \
> > +			return new handler(name);                           \
> > +		}                                                           \
> > +	};                                                                  \
> > +	static handler##Factory global_##handler##Factory;
> > +
> > +} /* namespace ipa */
> > +
> > +} /* namespace libcamera */
> > +
> > +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
> > +
> 
> No empty line at EOF otherwise git am complains (at least, that's how
> I interpret the error message :)
> 
> > diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> > index 038fc490..dc90542c 100644
> > --- a/src/ipa/libipa/meson.build
> > +++ b/src/ipa/libipa/meson.build
> > @@ -2,11 +2,13 @@
> >
> >  libipa_headers = files([
> >      'algorithm.h',
> > +    'camera_sensor_helper.h',
> >      'histogram.h'
> >  ])
> >
> >  libipa_sources = files([
> >      'algorithm.cpp',
> > +    'camera_sensor_helper.cpp',
> >      'histogram.cpp'
> >  ])
> >

Hi Naush,

On Tue, Jun 08, 2021 at 09:42:24AM +0100, Naushir Patuck wrote:
> On Mon, 7 Jun 2021 at 20:35, Jean-Michel Hautbois wrote:
> > On 07/06/2021 20:15, Jean-Michel Hautbois wrote:
> > > On 07/06/2021 19:31, Naushir Patuck wrote:
> > >> On Mon, 7 Jun 2021 at 13:35, Jean-Michel Hautbois wrote:
> > >>>
> > >>> Setting analogue gain for a specific sensor is not a straghtforward
> > >>> operation, as one needs to know how the gain is calculated for it.
> > >>>
> > >>> This commit introduces a new camera sensor helper in libipa which aims
> > >>> to solve this specific issue.
> > >>> It is based on the MIPI alliance Specification for Camera Command Set
> > >>> and implements, for now, only the analogue "Global gain" mode.
> > >>
> > >> I know this has probably been discussed in detail internally, but what provisions
> > >> do you expect for gain formulas that do not conform to the CCI formula, or  those
> > >> that are entirely table based?
> > >
> > > It has not been discussed in detail no, and I am sure I have missed a lot of cases.
> > > For those specific cases, we may, for instance, have a new value in
> > > AnalogueGainCapability enum and let the subclass calculate the proper value ?
> > > I don't have this case right now in my hands, so it is difficult to know
> > > precisely what is the best way to do so ;-).
> > >
> > >>> Is makes it possible to only have 4 parameters to store per sensor, and
> > >>> the gain calculation is then done identically for all of them. This
> > >>> commit gives the gains for imx219 (based on RPi cam_helper), ov5670 and
> > >>> ov5693.
> > >>>
> > >>> Adding a new sensor is pretty straightfoward as one only needs to
> > >>> implement the sub-class for it and register that class to the
> > >>> CameraSensorHelperFactory.
> > >>>
> > >>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com
> > >>> ---
> > >>>  src/ipa/libipa/camera_sensor_helper.cpp | 361++++++++++++++++++++++++
> > >>>  src/ipa/libipa/camera_sensor_helper.h   |  91 ++++++
> > >>>  src/ipa/libipa/meson.build              |   2 +
> > >>>  3 files changed, 454 insertions(+)
> > >>>  create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
> > >>>  create mode 100644 src/ipa/libipa/camera_sensor_helper.h
> > >>>
> > >>> diff --git a/src/ipa/libipa/camera_sensor_helper.cpp
> > >>> b/src/ipa/libipa/camera_sensor_helper.cpp
> > >>> new file mode 100644
> > >>> index 00000000..2bd82861
> > >>> --- /dev/null
> > >>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> > >>> @@ -0,0 +1,361 @@
> > >>> +/* SPDX-License-Identifier: BSD-2-Clause */
> > >>> +/*
> > >>> + * Copyright (C) 2021 Ideas On Board
> > >>> + *
> > >>> + * camera_sensor_helper.cpp - helper class providing camerainformations
> > >>> + */
> > >>> +#include "camera_sensor_helper.h"
> > >>> +
> > >>> +#include <map>
> > >>> +
> > >>> +#include "libcamera/internal/log.h"
> > >>> +
> > >>> +/**
> > >>> + * \file camera_sensor_helper.h
> > >>> + * \brief Create helper class for each sensor
> > >>> + *
> > >>> + * Each camera sensor supported by libcamera may need specificinformations to
> > >>> + * be sent (analogue gain is sensor dependant for instance).
> > >>> + *
> > >>> + * Every subclass of CameraSensorHelper shall be registered withlibipa using
> > >>> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> > >>> + */
> > >>> +
> > >>> +namespace libcamera {
> > >>> +
> > >>> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> > >>> +
> > >>> +namespace ipa {
> > >>> +
> > >>> +/**
> > >>> + * \class CameraSensorHelper
> > >>> + * \brief Create and give helpers for each camera sensor in thepipeline
> > >>> + *
> > >>> + * CameraSensorHelper instances are unique and sensor dependant.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \brief Construct a CameraSensorHelper instance
> > >>> + * \param[in] name The sensor model name
> > >>> + *
> > >>> + * The CameraSensorHelper instances shall never be constructedmanually, but always
> > >>> + * through the CameraSensorHelperFactory::create() methodimplemented by the
> > >>> + * respective factories.
> > >>> + */
> > >>> +
> > >>> +CameraSensorHelper::CameraSensorHelper(const char *name)
> > >>> +       : name_(name)
> > >>> +{
> > >>> +       analogueGain_ = { GlobalGain, 1, 1, 0, 0 };
> > >>> +}
> > >>> +
> > >>> +CameraSensorHelper::~CameraSensorHelper()
> > >>> +{
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelper::getGainCode(double gain)
> > >>> + * \brief Get the analogue gain code to pass to V4L2 subdev control
> > >>> + * \param[in] gain The real gain to pass
> > >>> + *
> > >>> + * This function aims to abstract the calculation of the gain letting the IPA
> > >>> + * use the real gain for its estimations.
> > >>> + *
> > >>> + * The parameters come from the MIPI Alliance Camera Specification for
> > >>> + * Camera Command Set (CCS).
> > >>> + */
> > >>> +uint32_t CameraSensorHelper::getGainCode(double gain) const
> > >>> +{
> > >>> +       /* \todo we only support the global gain mode for now */
> > >>> +       if (analogueGain_.type != GlobalGain)
> > >>> +               return UINT32_MAX;
> > >>> +
> > >>> +       if (analogueGain_.m0 == 0)
> > >>> +               return (analogueGain_.c0 - gain * analogueGain_.c1) / (gain * analogueGain_.m1);
> > >>> +       if (analogueGain_.m1 == 0)
> > >>> +               return (gain * analogueGain_.c1 - analogueGain_.c0) / analogueGain_.m0;
> > >>> +
> > >>> +       LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";
> > >>> +       return 1;
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelper::getGain
> > >>> + * \brief Get the real gain from the V4l2 subdev control gain
> > >>> + * \param[in] gainCode The V4l2 subdev control gain
> > >>> + *
> > >>> + * This function aims to abstract the calculation of the gain letting the IPA
> > >>> + * use the real gain for its estimations. It is the counterpart of the function
> > >>> + * CameraSensorHelper::getGainCode.
> > >>> + *
> > >>> + * The parameters come from the MIPI Alliance Camera Specification for
> > >>> + * Camera Command Set (CCS).
> > >>> + */
> > >>> +double CameraSensorHelper::getGain(uint32_t gainCode) const
> > >>> +{
> > >>> +       if (analogueGain_.type != GlobalGain)
> > >>> +               return UINT32_MAX;
> > >>> +
> > >>> +       if (analogueGain_.m0 == 0)
> > >>> +               return analogueGain_.c0 / (analogueGain_.m1 * gainCode + analogueGain_.c1);
> > >>> +       if (analogueGain_.m1 == 0)
> > >>> +               return (analogueGain_.m0 * gainCode + analogueGain_.c0) / analogueGain_.c1;
> > >>> +
> > >>> +       LOG(CameraSensorHelper, Error) << "For any given image sensor either m0 or m1 shall be zero.";
> > >>> +       return 1.0;
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelper::name()
> > >>> + * \brief Retrieve the camera sensor helper name
> > >>> + * \return The camera sensor helper name
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \enum CameraSensorHelper::AnalogueGainCapability
> > >>> + * \brief Specify the Gain mode supported by the sensor
> > >>> + *
> > >>> + * Describes the image sensor analog Gain capabilities.
> > >>> + * Two modes are possible, depending on the sensor: Global and Alternate.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::GlobalGain
> > >>> + * \brief Sensor supports Global gain
> > >>> + *
> > >>> + * The relationship between the integer Gain parameter and the resulting Gain
> > >>> + * multiplier is given by the following equation:
> > >>> + *
> > >>> + * \f$\frac{m0x+c0}{m1x+c1}\f$
> > >>> + *
> > >>> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> > >>> + * image-sensor-specific constants exposed by the sensor.
> > >>> + * These constants are static parameters, and for any given image sensor either
> > >>> + * m0 or m1 shall be zero.
> > >>> + *
> > >>> + * The full Gain equation therefore reduces to either:
> > >>> + *
> > >>> + * \f$\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::AlternateGlobalGain
> > >>> + * \brief Sensor supports Analogue Global gain (introduced in CCS v1.1)
> > >>> + *
> > >>> + * Starting with CCS v1.1, Alternate Global Analog Gain is alsoavailable.
> > >>> + * If the image sensor supports it, then the global analog Gain canbe controlled
> > >>> + * by linear and exponential gain formula:
> > >>> + *
> > >>> + * \f$gain = analogLinearGainGlobal *2^{analogExponentialGainGlobal} \f$
> > >>> + * \todo not implemented in libipa
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \struct CameraSensorHelper::analogueGainConstants
> > >>> + * \brief Analogue gain constants used for gain calculation
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::analogueGainConstants::type
> > >>> + * \brief Analogue gain coding type
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::analogueGainConstants::m0
> > >>> + * \brief Constant used in the analog Gain control coding/decoding.
> > >>> + *
> > >>> + * Note: either m0 or m1 shall be zero.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::analogueGainConstants::c0
> > >>> + * \brief Constant used in the analog Gain control coding/decoding.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::analogueGainConstants::m1
> > >>> + * \brief Constant used in the analog Gain control coding/decoding.
> > >>> + *
> > >>> + * Note: either m0 or m1 shall be zero.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::analogueGainConstants::c1
> > >>> + * \brief Constant used in the analog Gain control coding/decoding.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \var CameraSensorHelper::analogueGain_
> > >>> + * \brief The analogue gain parameters used for calculation
> > >>> + *
> > >>> + * The analogue gain is calculated through a formula, and itsparameters are
> > >>> + * sensor specific. Use this variable to store the values at init time.
> > >>> + *
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \class CameraSensorHelperFactory
> > >>> + * \brief Registration of CameraSensorHelperFactory classes andcreation of instances
> > >>> + *
> > >>> + * To facilitate discovery and instantiation of CameraSensorHelperclasses, the
> > >>> + * CameraSensorHelperFactory class maintains a registry of camerasensor helper
> > >>> + * classes. Each CameraSensorHelper subclass shall register itselfusing the
> > >>> + * REGISTER_CAMERA_SENSOR_HELPER() macro, which will create acorresponding
> > >>> + * instance of a CameraSensorHelperFactory subclass and register itwith the
> > >>> + * static list of factories.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \brief Construct a camera sensor helper factory
> > >>> + * \param[in] name Name of the camera sensor helper class
> > >>> + *
> > >>> + * Creating an instance of the factory registers it with the globallist of
> > >>> + * factories, accessible through the factories() function.
> > >>> + *
> > >>> + * The factory \a name is used for debug purpose and shall be unique.
> > >>> + */
> > >>> +
> > >>> +CameraSensorHelperFactory::CameraSensorHelperFactory(const char *name)
> > >>> +       : name_(name)
> > >>> +{
> > >>> +       registerType(this);
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \brief Create an instance of the CameraSensorHelpercorresponding to the factory
> > >>> + *
> > >>> + * \return A unique pointer to a new instance of theCameraSensorHelper subclass
> > >>> + * corresponding to the factory
> > >>> + */
> > >>> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create()
> > >>> +{
> > >>> +       CameraSensorHelper *handler = createInstance();
> > >>> +       return std::unique_ptr<CameraSensorHelper>(handler);
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelperFactory::name()
> > >>> + * \brief Retrieve the factory name
> > >>> + * \return The factory name
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \brief Add a camera sensor helper class to the registry
> > >>> + * \param[in] factory Factory to use to construct the camera sensorhelper
> > >>> + *
> > >>> + * The caller is responsible to guarantee the uniqueness of thecamera sensor helper
> > >>> + * name.
> > >>> + */
> > >>> +voidCameraSensorHelperFactory::registerType(CameraSensorHelperFactory*factory)
> > >>> +{
> > >>> +       std::vector<CameraSensorHelperFactory *> &factories =CameraSensorHelperFactory::factories();
> > >>> +
> > >>> +       factories.push_back(factory);
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \brief Retrieve the list of all camera sensor helper factories
> > >>> + *
> > >>> + * The static factories map is defined inside the function toensures it gets
> > >>> + * initialized on first use, without any dependency on link order.
> > >>> + *
> > >>> + * \return The list of camera sensor helper factories
> > >>> + */
> > >>> +std::vector<CameraSensorHelperFactory *>&CameraSensorHelperFactory::factories()
> > >>> +{
> > >>> +       static std::vector<CameraSensorHelperFactory *> factories;
> > >>> +       return factories;
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelperFactory::createInstance()
> > >>> + * \brief Create an instance of the CameraSensorHelpercorresponding to the factory
> > >>> + *
> > >>> + * This virtual function is implemented by theREGISTER_CAMERA_SENSOR_HELPER()
> > >>> + * macro. It creates a camera sensor helper instance associatedwith the camera
> > >>> + * sensor model.
> > >>> + *
> > >>> + * \return A pointer to a newly constructed instance of theCameraSensorHelper
> > >>> + * subclass corresponding to the factory
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \def REGISTER_CAMERA_SENSOR_HELPER
> > >>> + * \brief Register a camera sensor helper with the camera sensorhelper factory
> > >>> + * \param[in] name Sensor model name used to register the class
> > >>> + * \param[in] handler Class name of CameraSensorHelper derivedclass to register
> > >>> + *
> > >>> + * Register a CameraSensorHelper subclass with the factory and makeit available to
> > >>> + * try and match devices.
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \class CameraSensorHelperImx219
> > >>> + * \brief Create and give helpers for the imx219 sensor
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelperImx219::CameraSensorHelperImx219
> > >>> + * \brief Construct a CameraSensorHelperImx219 instance for imx219
> > >>> + * \param[in] name The sensor model name
> > >>> + */
> > >>> +class CameraSensorHelperImx219 : public CameraSensorHelper
> > >>> +{
> > >>> +public:
> > >>> +       CameraSensorHelperImx219(const char *name);
> > >>> +};
> > >>> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> > >>> +CameraSensorHelperImx219::CameraSensorHelperImx219(const char *name)
> > >>> +       : CameraSensorHelper(name)
> > >>> +{
> > >>> +       analogueGain_ = { GlobalGain, 0, -1, 256, 256 };
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \class CameraSensorHelperOv5670
> > >>> + * \brief Create and give helpers for the ov5670 sensor
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelperOv5670::CameraSensorHelperOv5670
> > >>> + * \brief Construct a CameraSensorHelperOv5670 instance for ov5670
> > >>> + * \param[in] name The sensor model name
> > >>> + */
> > >>> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> > >>> +{
> > >>> +public:
> > >>> +       CameraSensorHelperOv5670(const char *name);
> > >>> +};
> > >>> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> > >>> +CameraSensorHelperOv5670::CameraSensorHelperOv5670(const char *name)
> > >>> +       : CameraSensorHelper(name)
> > >>> +{
> > >>> +       analogueGain_ = { GlobalGain, 1, 0, 0, 256 };
> > >>> +}
> > >>> +
> > >>> +/**
> > >>> + * \class CameraSensorHelperOv5693
> > >>> + * \brief Create and give helpers for the ov5693 sensor
> > >>> + */
> > >>> +
> > >>> +/**
> > >>> + * \fn CameraSensorHelperOv5693::CameraSensorHelperOv5693
> > >>> + * \brief Construct a CameraSensorHelperOv5693 instance for ov5693
> > >>> + * \param[in] name The sensor model name
> > >>> + */
> > >>> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> > >>> +{
> > >>> +public:
> > >>> +       CameraSensorHelperOv5693(const char *name);
> > >>> +};
> > >>> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> > >>> +CameraSensorHelperOv5693::CameraSensorHelperOv5693(const char *name)
> > >>> +       : CameraSensorHelper(name)
> > >>> +{
> > >>> +       analogueGain_ = { GlobalGain, 1, 0, 0, 16 };
> > >>> +}
> > >>> +
> > >>> +} /* namespace ipa */
> > >>> +
> > >>> +} /* namespace libcamera */
> > >>> +
> > >>> diff --git a/src/ipa/libipa/camera_sensor_helper.h
> > >>> b/src/ipa/libipa/camera_sensor_helper.h
> > >>> new file mode 100644
> > >>> index 00000000..63031902
> > >>> --- /dev/null
> > >>> +++ b/src/ipa/libipa/camera_sensor_helper.h
> > >>> @@ -0,0 +1,91 @@
> > >>> +/* SPDX-License-Identifier: BSD-2-Clause */
> > >>> +/*
> > >>> + * Copyright (C) 2021 Ideas On Board
> > >>> + *
> > >>> + * camera_sensor_helper.h - helper class providing camera informations
> > >>> + */
> > >>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> > >>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> > >>> +
> > >>> +#include <stdint.h>
> > >>> +
> > >>> +#include <string>
> > >>> +
> > >>> +#include <libcamera/class.h>
> > >>> +#include <libcamera/object.h>
> > >>> +
> > >>> +namespace libcamera {
> > >>> +
> > >>> +namespace ipa {
> > >>> +
> > >>> +class CameraSensorHelper;
> > >>> +
> > >>> +class CameraSensorHelper : public Object
> > >>> +{
> > >>> +public:
> > >>> +       CameraSensorHelper(const char *name);
> > >>> +       virtual ~CameraSensorHelper();
> > >>> +
> > >>> +       const std::string &name() const { return name_; }
> > >>> +       uint32_t getGainCode(double gain) const;
> >
> > Would you prefer getGainCode and getGain to be virtual, having a default
> > meyhod in CameraSensorHelper and letting those beeing overriden if a
> > specific sensor needs to have a different formula ?
> 
> The Raspberry Pi CamHelper does keep these functions as virtual.  However,
> I know Laurent and others would have a preference of using static data where
> possible.  Perhaps just something to consider for the future rather than
> doing it now.

For sensors that depart from a handful of standard models, I think
virtual functions make sense.

> > >>> +       double getGain(uint32_t gainCode) const;
> > >>> +
> > >>> +protected:
> > >>> +       enum AnalogueGainCapability : uint16_t {
> > >>> +               GlobalGain = 0,
> > >>> +               AlternateGlobalGain = 2,
> > >>> +       };
> > >>> +
> > >>> +       struct analogueGainConstants {
> > >>> +               uint16_t type;
> > >>> +               int16_t m0;
> > >>> +               int16_t c0;
> > >>> +               int16_t m1;
> > >>> +               int16_t c1;
> > >>> +       };
> > >>> +       analogueGainConstants analogueGain_;
> > >>> +
> > >>> +private:
> > >>> +       std::string name_;
> > >>> +       friend class CameraSensorHelperFactory;
> > >>> +};
> > >>> +
> > >>> +class CameraSensorHelperFactory
> > >>> +{
> > >>> +public:
> > >>> +       CameraSensorHelperFactory(const char *name);
> > >>> +       virtual ~CameraSensorHelperFactory() = default;
> > >>> +
> > >>> +       std::unique_ptr<CameraSensorHelper> create();
> > >>> +
> > >>> +       const std::string &name() const { return name_; }
> > >>> +
> > >>> +       static void registerType(CameraSensorHelperFactory *factory);
> > >>> +       static std::vector<CameraSensorHelperFactory *> &factories();
> > >>> +
> > >>> +private:
> > >>> +       virtual CameraSensorHelper *createInstance() = 0;
> > >>> +
> > >>> +       std::string name_;
> > >>> +};
> > >>> +
> > >>> +#define REGISTER_CAMERA_SENSOR_HELPER(name, handler)        \
> > >>> +       class handler##Factory final : publicCameraSensorHelperFactory     \
> > >>> +       {       \
> > >>> +       public:       \
> > >>> +               handler##Factory() :CameraSensorHelperFactory(#handler) {} \
> > >>> +        \
> > >>> +       private:        \
> > >>> +               CameraSensorHelper *createInstance()        \
> > >>> +               {       \
> > >>> +                       return new handler(name);       \
> > >>> +               }       \
> > >>> +       };        \
> > >>> +       static handler##Factory global_##handler##Factory;
> > >>> +
> > >>> +} /* namespace ipa */
> > >>> +
> > >>> +} /* namespace libcamera */
> > >>> +
> > >>> +#endif /* __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__ */
> > >>> +
> > >>> diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
> > >>> index 038fc490..dc90542c 100644
> > >>> --- a/src/ipa/libipa/meson.build
> > >>> +++ b/src/ipa/libipa/meson.build
> > >>> @@ -2,11 +2,13 @@
> > >>>
> > >>>  libipa_headers = files([
> > >>>      'algorithm.h',
> > >>> +    'camera_sensor_helper.h',
> > >>>      'histogram.h'
> > >>>  ])
> > >>>
> > >>>  libipa_sources = files([
> > >>>      'algorithm.cpp',
> > >>> +    'camera_sensor_helper.cpp',
> > >>>      'histogram.cpp'
> > >>>  ])
> > >>>