[libcamera-devel,v6,1/2] ipa: Create a camera sensor helper class

12679 diff mbox series

For various sensor operations, it may be needed to do sensor specific
computations, like analogue gain or vertical blanking.

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

Three helpers are created in this patch: imx219, ov5670 and ov5693.

Adding a new sensor is pretty straightforward 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>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
---
 src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
 src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
 src/ipa/libipa/meson.build              |   2 +
 3 files changed, 407 insertions(+)
 create mode 100644 src/ipa/libipa/camera_sensor_helper.cpp
 create mode 100644 src/ipa/libipa/camera_sensor_helper.h

HI JM,

few minors below:

On 6/22/21 3:15 PM, Jean-Michel Hautbois wrote:
> For various sensor operations, it may be needed to do sensor specific
> computations, like analogue gain or vertical blanking.
>
> 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.
> Setting analogue gain for a specific sensor is not a straightforward
> operation, as one needs to know how the gain is calculated for it.
>
> Three helpers are created in this patch: imx219, ov5670 and ov5693.
>
> Adding a new sensor is pretty straightforward 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>
> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
> ---
>   src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>   src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>   src/ipa/libipa/meson.build              |   2 +
>   3 files changed, 407 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..a114ee73
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,318 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.cpp - Helper class that performs sensor-specific parameter computations
> + */
> +#include "camera_sensor_helper.h"
> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Helper class that performs sensor-specific parameter computations
> + *
> + * Computation of sensor configuration parameters is a sensor specific
> + * operation. Each CameraHelper derived class computes the value of
> + * configuration parameters, for example the analogue gain value, using
> + * sensor-specific functions and constants.
> + *
> + * Every subclass of CameraSensorHelper shall be registered with libipa using
> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.

+1

this is nice and how each CameraSensorHelper is registered down below. 
The usage of this macro is apt.

> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
> +
> +namespace ipa {
> +
> +/**
> + * \class CameraSensorHelper
> + * \brief Base class for computing sensor tuning parameters using sensor-specific constants
> + *
> + * CameraSensorHelper derived class instances are sensor specific. Each

minor: I would write this as for clarity:

   * Instances derived from CameraSensorHelper class are sensor specific. Each

> + * supported sensor will have an associated base class defined.
> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + *
> + * CameraSensorHelper derived class instances shall never be constructed manually
> + * but always through the CameraSensorHelperFactory::create() method.
> + */
> +
> +/**
> + * \brief Compute gain code from the analogue gain absolute 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).
> + *
> + * \return The gain code to pass to V4l2
> + */
> +uint32_t CameraSensorHelper::gainCode(double gain) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);

This won't yield a floating value, ever? In case, it does, are we OK 
returning it as uint32_t with loss of precision. I am not sure, I 
haven't read the spec or understand this (maybe it's right, since it's 
gain-"code")


> +}
> +
> +/**
> + * \brief Compute the real gain from the V4l2 subdev control gain code
> + * \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::gainCode.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + *
> + * \return The real gain
> + */
> +double CameraSensorHelper::gain(uint32_t gainCode) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.m0 * static_cast<double>(gainCode) + analogueGainConstants_.c0) /
> +	       (analogueGainConstants_.m1 * static_cast<double>(gainCode) + analogueGainConstants_.c1);
> +}
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainType
> + * \brief the gain calculation modes as defined by the MIPI CCS
s/the/The
> + *
> + * Describes the image sensor analogue gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainLinear
> + * \brief Gain is computed using linear gain estimation
> + *
> + * The relationship between the integer gain parameter and the resulting gain
> + * multiplier is given by the following equation:
> + *
> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainExponential
> + * \brief Gain is computed using exponential gain estimation (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
> + * If the image sensor supports it, then the global analogue 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 calculation mode
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m0
> + * \brief Constant used in the analogue Gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
s/either/Either
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c0
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m1
> + * \brief Constant used in the analogue gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
Same
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c1
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants_
> + * \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
s/classes./sub-classes. maybe?
> + * 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 std::string name)
> +	: name_(name)
> +{
> +	registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
> + * \param[in] name Name of the factory
> + *
> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
> + * corresponding to the factory
> + */
> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
> +{
> +	std::vector<CameraSensorHelperFactory *> &factories =
> +		CameraSensorHelperFactory::factories();
> +
> +	for (CameraSensorHelperFactory *factory : factories) {
> +		if (name != factory->name_)
> +			continue;
> +
> +		CameraSensorHelper *helper = factory->createInstance();
> +		return std::unique_ptr<CameraSensorHelper>(helper);
> +	}
> +
> +	return nullptr;
> +}
> +
> +/**
> + * \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
> + */
> +
> +/**
> + * \var CameraSensorHelperFactory::name_
> + * \brief The name of 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] helper Class name of CameraSensorHelper derived class to register
> + *
> + * Register a CameraSensorHelper subclass with the factory and make it available to
> + * try and match devices.

I do wonder about the reasons that registering a camera sensor helper 
needs to create a derived factory class first
and  then, it is responsible to create Instance(s) of that camera sensor 
helper per se?

Can CameraSensorHelper base class be flexible enough to create those 
instances by itself and keeping the registry internal?
I am not sure, there might be some road-blocks I am not able to see 
right now.

.... but this isn't that complicated either :-)

So,

Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

> + */
> +
> +/**
> + * \class CameraSensorHelperImx219
> + * \brief Create and give helpers for the imx219 sensor
> + */
> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperImx219()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5670()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5693()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +
> +} /* 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..c43e4bf6
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,87 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.h - Helper class that performs sensor-specific parameter computations
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <memory>
> +#include <string>
> +#include <vector>
> +
> +#include <libcamera/class.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelper() = default;
> +	virtual ~CameraSensorHelper() = default;
> +
> +	virtual uint32_t gainCode(double gain) const;
> +	virtual double gain(uint32_t gainCode) const;
> +
> +protected:
> +	enum AnalogueGainType {
> +		AnalogueGainLinear = 0,
> +		AnalogueGainExponential = 2,
> +	};
> +
> +	struct AnalogueGainConstants {
> +		AnalogueGainType type;
> +		int16_t m0;
> +		int16_t c0;
> +		int16_t m1;
> +		int16_t c1;
> +	};
> +
> +	AnalogueGainConstants analogueGainConstants_;
> +
> +private:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +	CameraSensorHelperFactory(const std::string name);
> +	virtual ~CameraSensorHelperFactory() = default;
> +
> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
> +
> +	static void registerType(CameraSensorHelperFactory *factory);
> +	static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +protected:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
> +	virtual CameraSensorHelper *createInstance() = 0;
> +
> +	std::string name_;
> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)		  \
> +class helper##Factory final : public CameraSensorHelperFactory	  \
> +{                                                                 \
> +public:                                                           \
> +	helper##Factory() : CameraSensorHelperFactory(name) {}	  \
> +								  \
> +private:                                                          \
> +	CameraSensorHelper *createInstance()			  \
> +	{							  \
> +		return new helper();				  \
> +	}							  \
> +};								  \
> +static helper##Factory global_##helper##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'
>   ])
>

Hi JM,

On 22/06/2021 10:45, Jean-Michel Hautbois wrote:
> For various sensor operations, it may be needed to do sensor specific
> computations, like analogue gain or vertical blanking.
> 
> 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.
> Setting analogue gain for a specific sensor is not a straightforward
> operation, as one needs to know how the gain is calculated for it.
> 
> Three helpers are created in this patch: imx219, ov5670 and ov5693.
> 
> Adding a new sensor is pretty straightforward 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>
> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 407 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..a114ee73
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,318 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.cpp - Helper class that performs sensor-specific parameter computations
> + */
> +#include "camera_sensor_helper.h"
> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Helper class that performs sensor-specific parameter computations
> + *
> + * Computation of sensor configuration parameters is a sensor specific
> + * operation. Each CameraHelper derived class computes the value of
> + * configuration parameters, for example the analogue gain value, using
> + * sensor-specific functions and constants.
> + *
> + * 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 Base class for computing sensor tuning parameters using sensor-specific constants
> + *
> + * CameraSensorHelper derived class instances are sensor specific. Each
> + * supported sensor will have an associated base class defined.
> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + *
> + * CameraSensorHelper derived class instances shall never be constructed manually
> + * but always through the CameraSensorHelperFactory::create() method.
> + */
> +
> +/**
> + * \brief Compute gain code from the analogue gain absolute 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).
> + *
> + * \return The gain code to pass to V4l2
> + */
> +uint32_t CameraSensorHelper::gainCode(double gain) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));

This doesn't need brackets around the two comparisons.

The == takes precedence over the || so those are evaluated before the
logical OR.

https://en.cppreference.com/w/cpp/language/operator_precedence

I personally don't mind over-scoping though, as it helps make sure
things are clear when order of precedence isn't always in peoples minds.


> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
> +}
> +
> +/**
> + * \brief Compute the real gain from the V4l2 subdev control gain code
> + * \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::gainCode.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + *
> + * \return The real gain
> + */
> +double CameraSensorHelper::gain(uint32_t gainCode) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));

Same,

> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.m0 * static_cast<double>(gainCode) + analogueGainConstants_.c0) /
> +	       (analogueGainConstants_.m1 * static_cast<double>(gainCode) + analogueGainConstants_.c1);

We're at v6, so I assume those calculations have been verified by now?

In particular all the type promotions ...


> +}
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainType
> + * \brief the gain calculation modes as defined by the MIPI CCS
> + *
> + * Describes the image sensor analogue gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainLinear
> + * \brief Gain is computed using linear gain estimation
> + *
> + * The relationship between the integer gain parameter and the resulting gain
> + * multiplier is given by the following equation:
> + *
> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainExponential
> + * \brief Gain is computed using exponential gain estimation (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
> + * If the image sensor supports it, then the global analogue 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 calculation mode
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m0
> + * \brief Constant used in the analogue Gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c0
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m1
> + * \brief Constant used in the analogue gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c1
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants_
> + * \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 std::string name)
> +	: name_(name)
> +{
> +	registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
> + * \param[in] name Name of the factory
> + *
> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
> + * corresponding to the factory
> + */
> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
> +{
> +	std::vector<CameraSensorHelperFactory *> &factories =
> +		CameraSensorHelperFactory::factories();
> +
> +	for (CameraSensorHelperFactory *factory : factories) {
> +		if (name != factory->name_)
> +			continue;
> +
> +		CameraSensorHelper *helper = factory->createInstance();
> +		return std::unique_ptr<CameraSensorHelper>(helper);
> +	}
> +
> +	return nullptr;
> +}
> +
> +/**
> + * \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
> + */
> +
> +/**
> + * \var CameraSensorHelperFactory::name_
> + * \brief The name of 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] helper 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
> + */
> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperImx219()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)

If these will grow, should we have one file per camera sensor helper to
split these out ?

Or is that overkill for the moment? I guess it can be broken out later
when new features are added that would make the scale increase.


Other than that, I don't want to block this series for things that can
continue in development so:

Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

and I'll let you decide if it should be split now or later.

--
Kieran



> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5670()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5693()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +
> +} /* 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..c43e4bf6
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,87 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.h - Helper class that performs sensor-specific parameter computations
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <memory>
> +#include <string>
> +#include <vector>
> +
> +#include <libcamera/class.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelper() = default;
> +	virtual ~CameraSensorHelper() = default;
> +
> +	virtual uint32_t gainCode(double gain) const;
> +	virtual double gain(uint32_t gainCode) const;
> +
> +protected:
> +	enum AnalogueGainType {
> +		AnalogueGainLinear = 0,
> +		AnalogueGainExponential = 2,
> +	};
> +
> +	struct AnalogueGainConstants {
> +		AnalogueGainType type;
> +		int16_t m0;
> +		int16_t c0;
> +		int16_t m1;
> +		int16_t c1;
> +	};
> +
> +	AnalogueGainConstants analogueGainConstants_;
> +
> +private:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +	CameraSensorHelperFactory(const std::string name);
> +	virtual ~CameraSensorHelperFactory() = default;
> +
> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
> +
> +	static void registerType(CameraSensorHelperFactory *factory);
> +	static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +protected:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
> +	virtual CameraSensorHelper *createInstance() = 0;
> +
> +	std::string name_;
> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)		  \
> +class helper##Factory final : public CameraSensorHelperFactory	  \
> +{                                                                 \
> +public:                                                           \
> +	helper##Factory() : CameraSensorHelperFactory(name) {}	  \
> +								  \
> +private:                                                          \
> +	CameraSensorHelper *createInstance()			  \
> +	{							  \
> +		return new helper();				  \
> +	}							  \
> +};								  \
> +static helper##Factory global_##helper##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'
>  ])
>  
>

Hi Kieran,

On 24/06/2021 14:46, Kieran Bingham wrote:
> Hi JM,
> 
> On 22/06/2021 10:45, Jean-Michel Hautbois wrote:
>> For various sensor operations, it may be needed to do sensor specific
>> computations, like analogue gain or vertical blanking.
>>
>> 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.
>> Setting analogue gain for a specific sensor is not a straightforward
>> operation, as one needs to know how the gain is calculated for it.
>>
>> Three helpers are created in this patch: imx219, ov5670 and ov5693.
>>
>> Adding a new sensor is pretty straightforward 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>
>> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
>> ---
>>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>>  src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>>  src/ipa/libipa/meson.build              |   2 +
>>  3 files changed, 407 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..a114ee73
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>> @@ -0,0 +1,318 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.cpp - Helper class that performs sensor-specific parameter computations
>> + */
>> +#include "camera_sensor_helper.h"
>> +
>> +#include "libcamera/internal/log.h"
>> +
>> +/**
>> + * \file camera_sensor_helper.h
>> + * \brief Helper class that performs sensor-specific parameter computations
>> + *
>> + * Computation of sensor configuration parameters is a sensor specific
>> + * operation. Each CameraHelper derived class computes the value of
>> + * configuration parameters, for example the analogue gain value, using
>> + * sensor-specific functions and constants.
>> + *
>> + * 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 Base class for computing sensor tuning parameters using sensor-specific constants
>> + *
>> + * CameraSensorHelper derived class instances are sensor specific. Each
>> + * supported sensor will have an associated base class defined.
>> + */
>> +
>> +/**
>> + * \brief Construct a CameraSensorHelper instance
>> + *
>> + * CameraSensorHelper derived class instances shall never be constructed manually
>> + * but always through the CameraSensorHelperFactory::create() method.
>> + */
>> +
>> +/**
>> + * \brief Compute gain code from the analogue gain absolute 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).
>> + *
>> + * \return The gain code to pass to V4l2
>> + */
>> +uint32_t CameraSensorHelper::gainCode(double gain) const
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> 
> This doesn't need brackets around the two comparisons.
> 
> The == takes precedence over the || so those are evaluated before the
> logical OR.
> 
> https://en.cppreference.com/w/cpp/language/operator_precedence
> 
> I personally don't mind over-scoping though, as it helps make sure
> things are clear when order of precedence isn't always in peoples minds.
> 

I like it that way to ease reading :-).

> 
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
>> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
>> +}
>> +
>> +/**
>> + * \brief Compute the real gain from the V4l2 subdev control gain code
>> + * \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::gainCode.
>> + *
>> + * The parameters come from the MIPI Alliance Camera Specification for
>> + * Camera Command Set (CCS).
>> + *
>> + * \return The real gain
>> + */
>> +double CameraSensorHelper::gain(uint32_t gainCode) const
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> 
> Same,
> 
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +	return (analogueGainConstants_.m0 * static_cast<double>(gainCode) + analogueGainConstants_.c0) /
>> +	       (analogueGainConstants_.m1 * static_cast<double>(gainCode) + analogueGainConstants_.c1);
> 
> We're at v6, so I assume those calculations have been verified by now?
> 
> In particular all the type promotions ...
> 

Which are a pain... :-p but in our case it should be ok as far as I can
tell...
Would you prefer to see explicit conversions before the return ?

> 
>> +}
>> +
>> +/**
>> + * \enum CameraSensorHelper::AnalogueGainType
>> + * \brief the gain calculation modes as defined by the MIPI CCS
>> + *
>> + * Describes the image sensor analogue gain capabilities.
>> + * Two modes are possible, depending on the sensor: Global and Alternate.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainLinear
>> + * \brief Gain is computed using linear gain estimation
>> + *
>> + * The relationship between the integer gain parameter and the resulting gain
>> + * multiplier is given by the following equation:
>> + *
>> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
>> + *
>> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
>> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainExponential
>> + * \brief Gain is computed using exponential gain estimation (introduced in CCS v1.1)
>> + *
>> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
>> + * If the image sensor supports it, then the global analogue 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 calculation mode
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>> + * \brief Constant used in the analogue Gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>> + * \brief Constant used in the analogue gain coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>> + * \brief Constant used in the analogue gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>> + * \brief Constant used in the analogue gain coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::analogueGainConstants_
>> + * \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 std::string name)
>> +	: name_(name)
>> +{
>> +	registerType(this);
>> +}
>> +
>> +/**
>> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
>> + * \param[in] name Name of the factory
>> + *
>> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
>> + * corresponding to the factory
>> + */
>> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
>> +{
>> +	std::vector<CameraSensorHelperFactory *> &factories =
>> +		CameraSensorHelperFactory::factories();
>> +
>> +	for (CameraSensorHelperFactory *factory : factories) {
>> +		if (name != factory->name_)
>> +			continue;
>> +
>> +		CameraSensorHelper *helper = factory->createInstance();
>> +		return std::unique_ptr<CameraSensorHelper>(helper);
>> +	}
>> +
>> +	return nullptr;
>> +}
>> +
>> +/**
>> + * \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
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelperFactory::name_
>> + * \brief The name of 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] helper 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
>> + */
>> +class CameraSensorHelperImx219 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperImx219()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> 
> If these will grow, should we have one file per camera sensor helper to
> split these out ?
> 
> Or is that overkill for the moment? I guess it can be broken out later
> when new features are added that would make the scale increase.
> 
> 
> Other than that, I don't want to block this series for things that can
> continue in development so:
> 
> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> 
> and I'll let you decide if it should be split now or later.
> 

Thank you... I won't split it now, but it will be in a short notice
probably ;-).

> --
> Kieran
> 
> 
> 
>> +
>> +/**
>> + * \class CameraSensorHelperOv5670
>> + * \brief Create and give helpers for the ov5670 sensor
>> + */
>> +class CameraSensorHelperOv5670 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperOv5670()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
>> +
>> +/**
>> + * \class CameraSensorHelperOv5693
>> + * \brief Create and give helpers for the ov5693 sensor
>> + */
>> +class CameraSensorHelperOv5693 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperOv5693()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
>> +
>> +} /* 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..c43e4bf6
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>> @@ -0,0 +1,87 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.h - Helper class that performs sensor-specific parameter computations
>> + */
>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +
>> +#include <stdint.h>
>> +
>> +#include <memory>
>> +#include <string>
>> +#include <vector>
>> +
>> +#include <libcamera/class.h>
>> +
>> +namespace libcamera {
>> +
>> +namespace ipa {
>> +
>> +class CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelper() = default;
>> +	virtual ~CameraSensorHelper() = default;
>> +
>> +	virtual uint32_t gainCode(double gain) const;
>> +	virtual double gain(uint32_t gainCode) const;
>> +
>> +protected:
>> +	enum AnalogueGainType {
>> +		AnalogueGainLinear = 0,
>> +		AnalogueGainExponential = 2,
>> +	};
>> +
>> +	struct AnalogueGainConstants {
>> +		AnalogueGainType type;
>> +		int16_t m0;
>> +		int16_t c0;
>> +		int16_t m1;
>> +		int16_t c1;
>> +	};
>> +
>> +	AnalogueGainConstants analogueGainConstants_;
>> +
>> +private:
>> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
>> +};
>> +
>> +class CameraSensorHelperFactory
>> +{
>> +public:
>> +	CameraSensorHelperFactory(const std::string name);
>> +	virtual ~CameraSensorHelperFactory() = default;
>> +
>> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
>> +
>> +	static void registerType(CameraSensorHelperFactory *factory);
>> +	static std::vector<CameraSensorHelperFactory *> &factories();
>> +
>> +protected:
>> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
>> +	virtual CameraSensorHelper *createInstance() = 0;
>> +
>> +	std::string name_;
>> +};
>> +
>> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)		  \
>> +class helper##Factory final : public CameraSensorHelperFactory	  \
>> +{                                                                 \
>> +public:                                                           \
>> +	helper##Factory() : CameraSensorHelperFactory(name) {}	  \
>> +								  \
>> +private:                                                          \
>> +	CameraSensorHelper *createInstance()			  \
>> +	{							  \
>> +		return new helper();				  \
>> +	}							  \
>> +};								  \
>> +static helper##Factory global_##helper##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'
>>  ])
>>  
>>

Hi Umang,

On 24/06/2021 13:45, Umang Jain wrote:
> HI JM,
> 
> few minors below:
> 
> On 6/22/21 3:15 PM, Jean-Michel Hautbois wrote:
>> For various sensor operations, it may be needed to do sensor specific
>> computations, like analogue gain or vertical blanking.
>>
>> 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.
>> Setting analogue gain for a specific sensor is not a straightforward
>> operation, as one needs to know how the gain is calculated for it.
>>
>> Three helpers are created in this patch: imx219, ov5670 and ov5693.
>>
>> Adding a new sensor is pretty straightforward 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>
>> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
>> ---
>>   src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>>   src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>>   src/ipa/libipa/meson.build              |   2 +
>>   3 files changed, 407 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..a114ee73
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>> @@ -0,0 +1,318 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.cpp - Helper class that performs
>> sensor-specific parameter computations
>> + */
>> +#include "camera_sensor_helper.h"
>> +
>> +#include "libcamera/internal/log.h"
>> +
>> +/**
>> + * \file camera_sensor_helper.h
>> + * \brief Helper class that performs sensor-specific parameter
>> computations
>> + *
>> + * Computation of sensor configuration parameters is a sensor specific
>> + * operation. Each CameraHelper derived class computes the value of
>> + * configuration parameters, for example the analogue gain value, using
>> + * sensor-specific functions and constants.
>> + *
>> + * Every subclass of CameraSensorHelper shall be registered with
>> libipa using
>> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
> 
> +1
> 
> this is nice and how each CameraSensorHelper is registered down below.
> The usage of this macro is apt.
> 
>> + */
>> +
>> +namespace libcamera {
>> +
>> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
>> +
>> +namespace ipa {
>> +
>> +/**
>> + * \class CameraSensorHelper
>> + * \brief Base class for computing sensor tuning parameters using
>> sensor-specific constants
>> + *
>> + * CameraSensorHelper derived class instances are sensor specific. Each
> 
> minor: I would write this as for clarity:
> 
>   * Instances derived from CameraSensorHelper class are sensor specific.
> Each
> 
>> + * supported sensor will have an associated base class defined.
>> + */
>> +
>> +/**
>> + * \brief Construct a CameraSensorHelper instance
>> + *
>> + * CameraSensorHelper derived class instances shall never be
>> constructed manually
>> + * but always through the CameraSensorHelperFactory::create() method.
>> + */
>> +
>> +/**
>> + * \brief Compute gain code from the analogue gain absolute 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).
>> + *
>> + * \return The gain code to pass to V4l2
>> + */
>> +uint32_t CameraSensorHelper::gainCode(double gain) const
>> +{
>> +    ASSERT((analogueGainConstants_.m0 == 0) ||
>> (analogueGainConstants_.m1 == 0));
>> +    ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +    return (analogueGainConstants_.c0 - analogueGainConstants_.c1 *
>> gain) /
>> +           (analogueGainConstants_.m1 * gain -
>> analogueGainConstants_.m0);
> 
> This won't yield a floating value, ever? In case, it does, are we OK
> returning it as uint32_t with loss of precision. I am not sure, I
> haven't read the spec or understand this (maybe it's right, since it's
> gain-"code")
> 
> 

I don't think so, but I can have intermediate values if it scares you :-).
The gain is a integer on kernel side, the loss of precision results in a
minor difference AFAIK.

>> +}
>> +
>> +/**
>> + * \brief Compute the real gain from the V4l2 subdev control gain code
>> + * \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::gainCode.
>> + *
>> + * The parameters come from the MIPI Alliance Camera Specification for
>> + * Camera Command Set (CCS).
>> + *
>> + * \return The real gain
>> + */
>> +double CameraSensorHelper::gain(uint32_t gainCode) const
>> +{
>> +    ASSERT((analogueGainConstants_.m0 == 0) ||
>> (analogueGainConstants_.m1 == 0));
>> +    ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +    return (analogueGainConstants_.m0 * static_cast<double>(gainCode)
>> + analogueGainConstants_.c0) /
>> +           (analogueGainConstants_.m1 * static_cast<double>(gainCode)
>> + analogueGainConstants_.c1);
>> +}
>> +
>> +/**
>> + * \enum CameraSensorHelper::AnalogueGainType
>> + * \brief the gain calculation modes as defined by the MIPI CCS
> s/the/The
>> + *
>> + * Describes the image sensor analogue gain capabilities.
>> + * Two modes are possible, depending on the sensor: Global and
>> Alternate.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainLinear
>> + * \brief Gain is computed using linear gain estimation
>> + *
>> + * The relationship between the integer gain parameter and the
>> resulting gain
>> + * multiplier is given by the following equation:
>> + *
>> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
>> + *
>> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
>> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainExponential
>> + * \brief Gain is computed using exponential gain estimation
>> (introduced in CCS v1.1)
>> + *
>> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also
>> available.
>> + * If the image sensor supports it, then the global analogue 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 calculation mode
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>> + * \brief Constant used in the analogue Gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
> s/either/Either
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>> + * \brief Constant used in the analogue gain coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>> + * \brief Constant used in the analogue gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
> Same
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>> + * \brief Constant used in the analogue gain coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::analogueGainConstants_
>> + * \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
> s/classes./sub-classes. maybe?
>> + * 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
>> std::string name)
>> +    : name_(name)
>> +{
>> +    registerType(this);
>> +}
>> +
>> +/**
>> + * \brief Create an instance of the CameraSensorHelper corresponding
>> to the factory
>> + * \param[in] name Name of the factory
>> + *
>> + * \return A unique pointer to a new instance of the
>> CameraSensorHelper subclass
>> + * corresponding to the factory
>> + */
>> +std::unique_ptr<CameraSensorHelper>
>> CameraSensorHelperFactory::create(const std::string &name)
>> +{
>> +    std::vector<CameraSensorHelperFactory *> &factories =
>> +        CameraSensorHelperFactory::factories();
>> +
>> +    for (CameraSensorHelperFactory *factory : factories) {
>> +        if (name != factory->name_)
>> +            continue;
>> +
>> +        CameraSensorHelper *helper = factory->createInstance();
>> +        return std::unique_ptr<CameraSensorHelper>(helper);
>> +    }
>> +
>> +    return nullptr;
>> +}
>> +
>> +/**
>> + * \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
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelperFactory::name_
>> + * \brief The name of 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] helper Class name of CameraSensorHelper derived class
>> to register
>> + *
>> + * Register a CameraSensorHelper subclass with the factory and make
>> it available to
>> + * try and match devices.
> 
> I do wonder about the reasons that registering a camera sensor helper
> needs to create a derived factory class first
> and  then, it is responsible to create Instance(s) of that camera sensor
> helper per se?
> 
> Can CameraSensorHelper base class be flexible enough to create those
> instances by itself and keeping the registry internal?
> I am not sure, there might be some road-blocks I am not able to see
> right now.
> 
> .... but this isn't that complicated either :-)
> 
> So,
> 
> Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

Thanks.

The way it is designed is based on a Factory design pattern, and mostly
comes from PipelineHandler implementation.
I like it that way and can't see an obvious performance gain to have it
keeping the registry. It is called only at init time, so we are not in a
rush :-).

> 
>> + */
>> +
>> +/**
>> + * \class CameraSensorHelperImx219
>> + * \brief Create and give helpers for the imx219 sensor
>> + */
>> +class CameraSensorHelperImx219 : public CameraSensorHelper
>> +{
>> +public:
>> +    CameraSensorHelperImx219()
>> +    {
>> +        analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256,
>> 256 };
>> +    }
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
>> +
>> +/**
>> + * \class CameraSensorHelperOv5670
>> + * \brief Create and give helpers for the ov5670 sensor
>> + */
>> +class CameraSensorHelperOv5670 : public CameraSensorHelper
>> +{
>> +public:
>> +    CameraSensorHelperOv5670()
>> +    {
>> +        analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
>> +    }
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
>> +
>> +/**
>> + * \class CameraSensorHelperOv5693
>> + * \brief Create and give helpers for the ov5693 sensor
>> + */
>> +class CameraSensorHelperOv5693 : public CameraSensorHelper
>> +{
>> +public:
>> +    CameraSensorHelperOv5693()
>> +    {
>> +        analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
>> +    }
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
>> +
>> +} /* 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..c43e4bf6
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>> @@ -0,0 +1,87 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.h - Helper class that performs
>> sensor-specific parameter computations
>> + */
>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +
>> +#include <stdint.h>
>> +
>> +#include <memory>
>> +#include <string>
>> +#include <vector>
>> +
>> +#include <libcamera/class.h>
>> +
>> +namespace libcamera {
>> +
>> +namespace ipa {
>> +
>> +class CameraSensorHelper
>> +{
>> +public:
>> +    CameraSensorHelper() = default;
>> +    virtual ~CameraSensorHelper() = default;
>> +
>> +    virtual uint32_t gainCode(double gain) const;
>> +    virtual double gain(uint32_t gainCode) const;
>> +
>> +protected:
>> +    enum AnalogueGainType {
>> +        AnalogueGainLinear = 0,
>> +        AnalogueGainExponential = 2,
>> +    };
>> +
>> +    struct AnalogueGainConstants {
>> +        AnalogueGainType type;
>> +        int16_t m0;
>> +        int16_t c0;
>> +        int16_t m1;
>> +        int16_t c1;
>> +    };
>> +
>> +    AnalogueGainConstants analogueGainConstants_;
>> +
>> +private:
>> +    LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
>> +};
>> +
>> +class CameraSensorHelperFactory
>> +{
>> +public:
>> +    CameraSensorHelperFactory(const std::string name);
>> +    virtual ~CameraSensorHelperFactory() = default;
>> +
>> +    static std::unique_ptr<CameraSensorHelper> create(const
>> std::string &name);
>> +
>> +    static void registerType(CameraSensorHelperFactory *factory);
>> +    static std::vector<CameraSensorHelperFactory *> &factories();
>> +
>> +protected:
>> +    LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
>> +    virtual CameraSensorHelper *createInstance() = 0;
>> +
>> +    std::string name_;
>> +};
>> +
>> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)          \
>> +class helper##Factory final : public CameraSensorHelperFactory      \
>> +{                                                                 \
>> +public:                                                           \
>> +    helper##Factory() : CameraSensorHelperFactory(name) {}      \
>> +                                  \
>> +private:                                                          \
>> +    CameraSensorHelper *createInstance()              \
>> +    {                              \
>> +        return new helper();                  \
>> +    }                              \
>> +};                                  \
>> +static helper##Factory global_##helper##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'
>>   ])
>>   
>

Hi JM,

On 6/28/21 1:45 PM, Jean-Michel Hautbois wrote:
> Hi Umang,
>
> On 24/06/2021 13:45, Umang Jain wrote:
>> HI JM,
>>
>> few minors below:
>>
>> On 6/22/21 3:15 PM, Jean-Michel Hautbois wrote:
>>> For various sensor operations, it may be needed to do sensor specific
>>> computations, like analogue gain or vertical blanking.
>>>
>>> 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.
>>> Setting analogue gain for a specific sensor is not a straightforward
>>> operation, as one needs to know how the gain is calculated for it.
>>>
>>> Three helpers are created in this patch: imx219, ov5670 and ov5693.
>>>
>>> Adding a new sensor is pretty straightforward 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>
>>> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
>>> ---
>>>    src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>>>    src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>>>    src/ipa/libipa/meson.build              |   2 +
>>>    3 files changed, 407 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..a114ee73
>>> --- /dev/null
>>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>>> @@ -0,0 +1,318 @@
>>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>>> +/*
>>> + * Copyright (C) 2021, Google Inc.
>>> + *
>>> + * camera_sensor_helper.cpp - Helper class that performs
>>> sensor-specific parameter computations
>>> + */
>>> +#include "camera_sensor_helper.h"
>>> +
>>> +#include "libcamera/internal/log.h"
>>> +
>>> +/**
>>> + * \file camera_sensor_helper.h
>>> + * \brief Helper class that performs sensor-specific parameter
>>> computations
>>> + *
>>> + * Computation of sensor configuration parameters is a sensor specific
>>> + * operation. Each CameraHelper derived class computes the value of
>>> + * configuration parameters, for example the analogue gain value, using
>>> + * sensor-specific functions and constants.
>>> + *
>>> + * Every subclass of CameraSensorHelper shall be registered with
>>> libipa using
>>> + * the REGISTER_CAMERA_SENSOR_HELPER() macro.
>> +1
>>
>> this is nice and how each CameraSensorHelper is registered down below.
>> The usage of this macro is apt.
>>
>>> + */
>>> +
>>> +namespace libcamera {
>>> +
>>> +LOG_DEFINE_CATEGORY(CameraSensorHelper)
>>> +
>>> +namespace ipa {
>>> +
>>> +/**
>>> + * \class CameraSensorHelper
>>> + * \brief Base class for computing sensor tuning parameters using
>>> sensor-specific constants
>>> + *
>>> + * CameraSensorHelper derived class instances are sensor specific. Each
>> minor: I would write this as for clarity:
>>
>>    * Instances derived from CameraSensorHelper class are sensor specific.
>> Each
>>
>>> + * supported sensor will have an associated base class defined.
>>> + */
>>> +
>>> +/**
>>> + * \brief Construct a CameraSensorHelper instance
>>> + *
>>> + * CameraSensorHelper derived class instances shall never be
>>> constructed manually
>>> + * but always through the CameraSensorHelperFactory::create() method.
>>> + */
>>> +
>>> +/**
>>> + * \brief Compute gain code from the analogue gain absolute 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).
>>> + *
>>> + * \return The gain code to pass to V4l2
>>> + */
>>> +uint32_t CameraSensorHelper::gainCode(double gain) const
>>> +{
>>> +    ASSERT((analogueGainConstants_.m0 == 0) ||
>>> (analogueGainConstants_.m1 == 0));
>>> +    ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>>> +
>>> +    return (analogueGainConstants_.c0 - analogueGainConstants_.c1 *
>>> gain) /
>>> +           (analogueGainConstants_.m1 * gain -
>>> analogueGainConstants_.m0);
>> This won't yield a floating value, ever? In case, it does, are we OK
>> returning it as uint32_t with loss of precision. I am not sure, I
>> haven't read the spec or understand this (maybe it's right, since it's
>> gain-"code")
>>
>>
> I don't think so, but I can have intermediate values if it scares you :-).
> The gain is a integer on kernel side, the loss of precision results in a
> minor difference AFAIK.


hmm, in that case, I think you can capture this context as a small-ish 
comment here, describing that, one can except intermediate values on 
division but gain is an integer on kernel side...

>
>>> +}
>>> +
>>> +/**
>>> + * \brief Compute the real gain from the V4l2 subdev control gain code
>>> + * \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::gainCode.
>>> + *
>>> + * The parameters come from the MIPI Alliance Camera Specification for
>>> + * Camera Command Set (CCS).
>>> + *
>>> + * \return The real gain
>>> + */
>>> +double CameraSensorHelper::gain(uint32_t gainCode) const
>>> +{
>>> +    ASSERT((analogueGainConstants_.m0 == 0) ||
>>> (analogueGainConstants_.m1 == 0));
>>> +    ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>>> +
>>> +    return (analogueGainConstants_.m0 * static_cast<double>(gainCode)
>>> + analogueGainConstants_.c0) /
>>> +           (analogueGainConstants_.m1 * static_cast<double>(gainCode)
>>> + analogueGainConstants_.c1);
>>> +}
>>> +
>>> +/**
>>> + * \enum CameraSensorHelper::AnalogueGainType
>>> + * \brief the gain calculation modes as defined by the MIPI CCS
>> s/the/The
>>> + *
>>> + * Describes the image sensor analogue gain capabilities.
>>> + * Two modes are possible, depending on the sensor: Global and
>>> Alternate.
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainLinear
>>> + * \brief Gain is computed using linear gain estimation
>>> + *
>>> + * The relationship between the integer gain parameter and the
>>> resulting gain
>>> + * multiplier is given by the following equation:
>>> + *
>>> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
>>> + *
>>> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
>>> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainExponential
>>> + * \brief Gain is computed using exponential gain estimation
>>> (introduced in CCS v1.1)
>>> + *
>>> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also
>>> available.
>>> + * If the image sensor supports it, then the global analogue 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 calculation mode
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>>> + * \brief Constant used in the analogue Gain coding/decoding
>>> + *
>>> + * \note either m0 or m1 shall be zero.
>> s/either/Either
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>>> + * \brief Constant used in the analogue gain coding/decoding
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>>> + * \brief Constant used in the analogue gain coding/decoding
>>> + *
>>> + * \note either m0 or m1 shall be zero.
>> Same
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>>> + * \brief Constant used in the analogue gain coding/decoding
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelper::analogueGainConstants_
>>> + * \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
>> s/classes./sub-classes. maybe?
>>> + * 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
>>> std::string name)
>>> +    : name_(name)
>>> +{
>>> +    registerType(this);
>>> +}
>>> +
>>> +/**
>>> + * \brief Create an instance of the CameraSensorHelper corresponding
>>> to the factory
>>> + * \param[in] name Name of the factory
>>> + *
>>> + * \return A unique pointer to a new instance of the
>>> CameraSensorHelper subclass
>>> + * corresponding to the factory
>>> + */
>>> +std::unique_ptr<CameraSensorHelper>
>>> CameraSensorHelperFactory::create(const std::string &name)
>>> +{
>>> +    std::vector<CameraSensorHelperFactory *> &factories =
>>> +        CameraSensorHelperFactory::factories();
>>> +
>>> +    for (CameraSensorHelperFactory *factory : factories) {
>>> +        if (name != factory->name_)
>>> +            continue;
>>> +
>>> +        CameraSensorHelper *helper = factory->createInstance();
>>> +        return std::unique_ptr<CameraSensorHelper>(helper);
>>> +    }
>>> +
>>> +    return nullptr;
>>> +}
>>> +
>>> +/**
>>> + * \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
>>> + */
>>> +
>>> +/**
>>> + * \var CameraSensorHelperFactory::name_
>>> + * \brief The name of 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] helper Class name of CameraSensorHelper derived class
>>> to register
>>> + *
>>> + * Register a CameraSensorHelper subclass with the factory and make
>>> it available to
>>> + * try and match devices.
>> I do wonder about the reasons that registering a camera sensor helper
>> needs to create a derived factory class first
>> and  then, it is responsible to create Instance(s) of that camera sensor
>> helper per se?
>>
>> Can CameraSensorHelper base class be flexible enough to create those
>> instances by itself and keeping the registry internal?
>> I am not sure, there might be some road-blocks I am not able to see
>> right now.
>>
>> .... but this isn't that complicated either :-)
>>
>> So,
>>
>> Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
> Thanks.
>
> The way it is designed is based on a Factory design pattern, and mostly
> comes from PipelineHandler implementation.
> I like it that way and can't see an obvious performance gain to have it
> keeping the registry. It is called only at init time, so we are not in a
> rush :-).
>
>>> + */
>>> +
>>> +/**
>>> + * \class CameraSensorHelperImx219
>>> + * \brief Create and give helpers for the imx219 sensor
>>> + */
>>> +class CameraSensorHelperImx219 : public CameraSensorHelper
>>> +{
>>> +public:
>>> +    CameraSensorHelperImx219()
>>> +    {
>>> +        analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256,
>>> 256 };
>>> +    }
>>> +};
>>> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
>>> +
>>> +/**
>>> + * \class CameraSensorHelperOv5670
>>> + * \brief Create and give helpers for the ov5670 sensor
>>> + */
>>> +class CameraSensorHelperOv5670 : public CameraSensorHelper
>>> +{
>>> +public:
>>> +    CameraSensorHelperOv5670()
>>> +    {
>>> +        analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
>>> +    }
>>> +};
>>> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
>>> +
>>> +/**
>>> + * \class CameraSensorHelperOv5693
>>> + * \brief Create and give helpers for the ov5693 sensor
>>> + */
>>> +class CameraSensorHelperOv5693 : public CameraSensorHelper
>>> +{
>>> +public:
>>> +    CameraSensorHelperOv5693()
>>> +    {
>>> +        analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
>>> +    }
>>> +};
>>> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
>>> +
>>> +} /* 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..c43e4bf6
>>> --- /dev/null
>>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>>> @@ -0,0 +1,87 @@
>>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>>> +/*
>>> + * Copyright (C) 2021, Google Inc.
>>> + *
>>> + * camera_sensor_helper.h - Helper class that performs
>>> sensor-specific parameter computations
>>> + */
>>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>>> +
>>> +#include <stdint.h>
>>> +
>>> +#include <memory>
>>> +#include <string>
>>> +#include <vector>
>>> +
>>> +#include <libcamera/class.h>
>>> +
>>> +namespace libcamera {
>>> +
>>> +namespace ipa {
>>> +
>>> +class CameraSensorHelper
>>> +{
>>> +public:
>>> +    CameraSensorHelper() = default;
>>> +    virtual ~CameraSensorHelper() = default;
>>> +
>>> +    virtual uint32_t gainCode(double gain) const;
>>> +    virtual double gain(uint32_t gainCode) const;
>>> +
>>> +protected:
>>> +    enum AnalogueGainType {
>>> +        AnalogueGainLinear = 0,
>>> +        AnalogueGainExponential = 2,
>>> +    };
>>> +
>>> +    struct AnalogueGainConstants {
>>> +        AnalogueGainType type;
>>> +        int16_t m0;
>>> +        int16_t c0;
>>> +        int16_t m1;
>>> +        int16_t c1;
>>> +    };
>>> +
>>> +    AnalogueGainConstants analogueGainConstants_;
>>> +
>>> +private:
>>> +    LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
>>> +};
>>> +
>>> +class CameraSensorHelperFactory
>>> +{
>>> +public:
>>> +    CameraSensorHelperFactory(const std::string name);
>>> +    virtual ~CameraSensorHelperFactory() = default;
>>> +
>>> +    static std::unique_ptr<CameraSensorHelper> create(const
>>> std::string &name);
>>> +
>>> +    static void registerType(CameraSensorHelperFactory *factory);
>>> +    static std::vector<CameraSensorHelperFactory *> &factories();
>>> +
>>> +protected:
>>> +    LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
>>> +    virtual CameraSensorHelper *createInstance() = 0;
>>> +
>>> +    std::string name_;
>>> +};
>>> +
>>> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)          \
>>> +class helper##Factory final : public CameraSensorHelperFactory      \
>>> +{                                                                 \
>>> +public:                                                           \
>>> +    helper##Factory() : CameraSensorHelperFactory(name) {}      \
>>> +                                  \
>>> +private:                                                          \
>>> +    CameraSensorHelper *createInstance()              \
>>> +    {                              \
>>> +        return new helper();                  \
>>> +    }                              \
>>> +};                                  \
>>> +static helper##Factory global_##helper##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'
>>>    ])
>>>

Hi Jean-Michel,

I know this has been merged already, I should have reviewed this series
sooner. Could you please address the issues pointed out below in a new
series ?

On Tue, Jun 22, 2021 at 11:45:22AM +0200, Jean-Michel Hautbois wrote:
> For various sensor operations, it may be needed to do sensor specific
> computations, like analogue gain or vertical blanking.
> 
> 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.
> Setting analogue gain for a specific sensor is not a straightforward
> operation, as one needs to know how the gain is calculated for it.
> 
> Three helpers are created in this patch: imx219, ov5670 and ov5693.
> 
> Adding a new sensor is pretty straightforward 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>
> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 407 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..a114ee73
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,318 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.cpp - Helper class that performs sensor-specific parameter computations

Line break at 80 columns ? There are some long lines below that can be
easily broken at the 80 columns limit too (such as the \brief for the
CameraSensorClass for instance).

> + */
> +#include "camera_sensor_helper.h"
> +
> +#include "libcamera/internal/log.h"

This has turned into "libcamera/base/log.h" but it should be
<libcamera/base/log.h>.

> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Helper class that performs sensor-specific parameter computations
> + *
> + * Computation of sensor configuration parameters is a sensor specific

s/sensor specific/sensor-specific/

> + * operation. Each CameraHelper derived class computes the value of
> + * configuration parameters, for example the analogue gain value, using
> + * sensor-specific functions and constants.
> + *
> + * 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 Base class for computing sensor tuning parameters using sensor-specific constants
> + *
> + * CameraSensorHelper derived class instances are sensor specific. Each
> + * supported sensor will have an associated base class defined.
> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + *
> + * CameraSensorHelper derived class instances shall never be constructed manually
> + * but always through the CameraSensorHelperFactory::create() method.
> + */
> +
> +/**
> + * \brief Compute gain code from the analogue gain absolute 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).
> + *
> + * \return The gain code to pass to V4l2

s/V4l2/V4L2/

Same below.

It's however not very nice to make this aware of V4L2. I'll propose a
patch to improve the documentation, which will also define the concept
of gain code explicitly.

> + */
> +uint32_t CameraSensorHelper::gainCode(double gain) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));

No need for the inner parentheses. Same below.

> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
> +}
> +
> +/**
> + * \brief Compute the real gain from the V4l2 subdev control gain code
> + * \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::gainCode.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + *
> + * \return The real gain
> + */
> +double CameraSensorHelper::gain(uint32_t gainCode) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.m0 * static_cast<double>(gainCode) + analogueGainConstants_.c0) /
> +	       (analogueGainConstants_.m1 * static_cast<double>(gainCode) + analogueGainConstants_.c1);
> +}
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainType
> + * \brief the gain calculation modes as defined by the MIPI CCS
> + *
> + * Describes the image sensor analogue gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.

They're called Linear and Exponential here. Mentioning CCS for reference
is fine, but this is our implementation, with our names.

> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainLinear
> + * \brief Gain is computed using linear gain estimation
> + *
> + * The relationship between the integer gain parameter and the resulting gain
> + * multiplier is given by the following equation:
> + *
> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainExponential
> + * \brief Gain is computed using exponential gain estimation (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
> + * If the image sensor supports it, then the global analogue 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 calculation mode
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m0
> + * \brief Constant used in the analogue Gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c0
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m1
> + * \brief Constant used in the analogue gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c1
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants_
> + * \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 std::string name)
> +	: name_(name)
> +{
> +	registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory

s/the factory/a named factory/

PipelineHandlerFactory::create() is not a static function, so it's
different.

> + * \param[in] name Name of the factory
> + *
> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
> + * corresponding to the factory

s/the factory/the named factory, or a null pointer if no such factory exists/

> + */
> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
> +{
> +	std::vector<CameraSensorHelperFactory *> &factories =
> +		CameraSensorHelperFactory::factories();
> +
> +	for (CameraSensorHelperFactory *factory : factories) {
> +		if (name != factory->name_)
> +			continue;
> +
> +		CameraSensorHelper *helper = factory->createInstance();
> +		return std::unique_ptr<CameraSensorHelper>(helper);
> +	}
> +
> +	return nullptr;
> +}
> +
> +/**
> + * \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();

Line wrap.

> +
> +	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.

I know this comes from pipeline_handler.cpp, but this doesn't belong to
the API documentation, it's an implementation detail. You can move this
comment inside the function. Bonus points if you also fix the issue in
pipeline_handler.cpp.

> + *
> + * \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
> + */
> +
> +/**
> + * \var CameraSensorHelperFactory::name_
> + * \brief The name of 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] helper Class name of CameraSensorHelper derived class to register
> + *
> + * Register a CameraSensorHelper subclass with the factory and make it available to
> + * try and match devices.

s/devices/sensors/

> + */
> +
> +/**
> + * \class CameraSensorHelperImx219
> + * \brief Create and give helpers for the imx219 sensor
> + */

You can drop the comments for the subclasses, they don't bring any
value. If doxygen complains, you can enclose all the subclasses with a

#ifndef __DOXYGEN__
...
#endif /* __DOXYGEN__ */

You could also add a

/* -----------------------------------------------------------------------------
 * Sensor-speficic subclasses
 */

comment here if you want to separate it from the generic code above.

> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperImx219()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5670()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5693()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +
> +} /* 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..c43e4bf6
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,87 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.h - Helper class that performs sensor-specific parameter computations
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <memory>
> +#include <string>
> +#include <vector>
> +
> +#include <libcamera/class.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelper() = default;
> +	virtual ~CameraSensorHelper() = default;
> +
> +	virtual uint32_t gainCode(double gain) const;
> +	virtual double gain(uint32_t gainCode) const;
> +
> +protected:
> +	enum AnalogueGainType {
> +		AnalogueGainLinear = 0,
> +		AnalogueGainExponential = 2,

Why 2 and not 1 ? I'd actually drop the numerical values completely.

> +	};
> +
> +	struct AnalogueGainConstants {
> +		AnalogueGainType type;
> +		int16_t m0;
> +		int16_t c0;
> +		int16_t m1;
> +		int16_t c1;
> +	};
> +
> +	AnalogueGainConstants analogueGainConstants_;
> +
> +private:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +	CameraSensorHelperFactory(const std::string name);
> +	virtual ~CameraSensorHelperFactory() = default;
> +
> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
> +
> +	static void registerType(CameraSensorHelperFactory *factory);
> +	static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +protected:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)

This should be private.

> +	virtual CameraSensorHelper *createInstance() = 0;
> +
> +	std::string name_;

I think this can be private too.

protected:
	virtual CameraSensorHelper *createInstance() = 0;

private:
	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)

	std::string name_;

> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)		  \
> +class helper##Factory final : public CameraSensorHelperFactory	  \
> +{                                                                 \

We use tabs for indentation.

> +public:                                                           \
> +	helper##Factory() : CameraSensorHelperFactory(name) {}	  \
> +								  \
> +private:                                                          \
> +	CameraSensorHelper *createInstance()			  \
> +	{							  \
> +		return new helper();				  \
> +	}							  \
> +};								  \
> +static helper##Factory global_##helper##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'
>  ])
>

Hi JM,

On 22/06/2021 10:45, Jean-Michel Hautbois wrote:
> For various sensor operations, it may be needed to do sensor specific
> computations, like analogue gain or vertical blanking.
> 
> 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.
> Setting analogue gain for a specific sensor is not a straightforward
> operation, as one needs to know how the gain is calculated for it.
> 
> Three helpers are created in this patch: imx219, ov5670 and ov5693.
> 
> Adding a new sensor is pretty straightforward as one only needs to
> implement the sub-class for it and register that class to the
> CameraSensorHelperFactory.

While extending the factories to add a new class seems simple, I'm
having a hard time to determine what the 'correct' way to extend it is.

How would I determine the correct values for each of the fields for
instance?

Is there any guidance on where this information comes from or how it
should be determined? or are they values you already had somewhere?

For instance, we now need to add the ov13858, which is on the Soraka.

What should we follow to add that ?

I've added defaults by copying another as an example, but that's no
different to us supplying incorrect defaults otherwise.

I think outright failure when this data isn't provided is a better
option here though (which is what has happened to me), as it forces the
user to find out how to get the right values, and make sure they are
added - but the easier it is to demonstrate how to do that correctly,
the better.

--
Kieran


> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
> ---
>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>  src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>  src/ipa/libipa/meson.build              |   2 +
>  3 files changed, 407 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..a114ee73
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
> @@ -0,0 +1,318 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.cpp - Helper class that performs sensor-specific parameter computations
> + */
> +#include "camera_sensor_helper.h"
> +
> +#include "libcamera/internal/log.h"
> +
> +/**
> + * \file camera_sensor_helper.h
> + * \brief Helper class that performs sensor-specific parameter computations
> + *
> + * Computation of sensor configuration parameters is a sensor specific
> + * operation. Each CameraHelper derived class computes the value of
> + * configuration parameters, for example the analogue gain value, using
> + * sensor-specific functions and constants.
> + *
> + * 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 Base class for computing sensor tuning parameters using sensor-specific constants
> + *
> + * CameraSensorHelper derived class instances are sensor specific. Each
> + * supported sensor will have an associated base class defined.
> + */
> +
> +/**
> + * \brief Construct a CameraSensorHelper instance
> + *
> + * CameraSensorHelper derived class instances shall never be constructed manually
> + * but always through the CameraSensorHelperFactory::create() method.
> + */
> +
> +/**
> + * \brief Compute gain code from the analogue gain absolute 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).
> + *
> + * \return The gain code to pass to V4l2
> + */
> +uint32_t CameraSensorHelper::gainCode(double gain) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
> +}
> +
> +/**
> + * \brief Compute the real gain from the V4l2 subdev control gain code
> + * \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::gainCode.
> + *
> + * The parameters come from the MIPI Alliance Camera Specification for
> + * Camera Command Set (CCS).
> + *
> + * \return The real gain
> + */
> +double CameraSensorHelper::gain(uint32_t gainCode) const
> +{
> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
> +
> +	return (analogueGainConstants_.m0 * static_cast<double>(gainCode) + analogueGainConstants_.c0) /
> +	       (analogueGainConstants_.m1 * static_cast<double>(gainCode) + analogueGainConstants_.c1);
> +}
> +
> +/**
> + * \enum CameraSensorHelper::AnalogueGainType
> + * \brief the gain calculation modes as defined by the MIPI CCS
> + *
> + * Describes the image sensor analogue gain capabilities.
> + * Two modes are possible, depending on the sensor: Global and Alternate.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainLinear
> + * \brief Gain is computed using linear gain estimation
> + *
> + * The relationship between the integer gain parameter and the resulting gain
> + * multiplier is given by the following equation:
> + *
> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
> + *
> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainExponential
> + * \brief Gain is computed using exponential gain estimation (introduced in CCS v1.1)
> + *
> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
> + * If the image sensor supports it, then the global analogue 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 calculation mode
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m0
> + * \brief Constant used in the analogue Gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c0
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::m1
> + * \brief Constant used in the analogue gain coding/decoding
> + *
> + * \note either m0 or m1 shall be zero.
> + */
> +
> +/**
> + * \var CameraSensorHelper::AnalogueGainConstants::c1
> + * \brief Constant used in the analogue gain coding/decoding
> + */
> +
> +/**
> + * \var CameraSensorHelper::analogueGainConstants_
> + * \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 std::string name)
> +	: name_(name)
> +{
> +	registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
> + * \param[in] name Name of the factory
> + *
> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
> + * corresponding to the factory
> + */
> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
> +{
> +	std::vector<CameraSensorHelperFactory *> &factories =
> +		CameraSensorHelperFactory::factories();
> +
> +	for (CameraSensorHelperFactory *factory : factories) {
> +		if (name != factory->name_)
> +			continue;
> +
> +		CameraSensorHelper *helper = factory->createInstance();
> +		return std::unique_ptr<CameraSensorHelper>(helper);
> +	}
> +
> +	return nullptr;
> +}
> +
> +/**
> + * \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
> + */
> +
> +/**
> + * \var CameraSensorHelperFactory::name_
> + * \brief The name of 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] helper 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
> + */
> +class CameraSensorHelperImx219 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperImx219()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
> +
> +/**
> + * \class CameraSensorHelperOv5670
> + * \brief Create and give helpers for the ov5670 sensor
> + */
> +class CameraSensorHelperOv5670 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5670()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
> +
> +/**
> + * \class CameraSensorHelperOv5693
> + * \brief Create and give helpers for the ov5693 sensor
> + */
> +class CameraSensorHelperOv5693 : public CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelperOv5693()
> +	{
> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
> +	}
> +};
> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
> +
> +} /* 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..c43e4bf6
> --- /dev/null
> +++ b/src/ipa/libipa/camera_sensor_helper.h
> @@ -0,0 +1,87 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * camera_sensor_helper.h - Helper class that performs sensor-specific parameter computations
> + */
> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
> +
> +#include <stdint.h>
> +
> +#include <memory>
> +#include <string>
> +#include <vector>
> +
> +#include <libcamera/class.h>
> +
> +namespace libcamera {
> +
> +namespace ipa {
> +
> +class CameraSensorHelper
> +{
> +public:
> +	CameraSensorHelper() = default;
> +	virtual ~CameraSensorHelper() = default;
> +
> +	virtual uint32_t gainCode(double gain) const;
> +	virtual double gain(uint32_t gainCode) const;
> +
> +protected:
> +	enum AnalogueGainType {
> +		AnalogueGainLinear = 0,
> +		AnalogueGainExponential = 2,
> +	};
> +
> +	struct AnalogueGainConstants {
> +		AnalogueGainType type;
> +		int16_t m0;
> +		int16_t c0;
> +		int16_t m1;
> +		int16_t c1;
> +	};
> +
> +	AnalogueGainConstants analogueGainConstants_;
> +
> +private:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
> +};
> +
> +class CameraSensorHelperFactory
> +{
> +public:
> +	CameraSensorHelperFactory(const std::string name);
> +	virtual ~CameraSensorHelperFactory() = default;
> +
> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
> +
> +	static void registerType(CameraSensorHelperFactory *factory);
> +	static std::vector<CameraSensorHelperFactory *> &factories();
> +
> +protected:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
> +	virtual CameraSensorHelper *createInstance() = 0;
> +
> +	std::string name_;
> +};
> +
> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)		  \
> +class helper##Factory final : public CameraSensorHelperFactory	  \
> +{                                                                 \
> +public:                                                           \
> +	helper##Factory() : CameraSensorHelperFactory(name) {}	  \
> +								  \
> +private:                                                          \
> +	CameraSensorHelper *createInstance()			  \
> +	{							  \
> +		return new helper();				  \
> +	}							  \
> +};								  \
> +static helper##Factory global_##helper##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'
>  ])
>  
>

Hi Kieran,

On 29/06/2021 14:44, Kieran Bingham wrote:
> Hi JM,
> 
> On 22/06/2021 10:45, Jean-Michel Hautbois wrote:
>> For various sensor operations, it may be needed to do sensor specific
>> computations, like analogue gain or vertical blanking.
>>
>> 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.
>> Setting analogue gain for a specific sensor is not a straightforward
>> operation, as one needs to know how the gain is calculated for it.
>>
>> Three helpers are created in this patch: imx219, ov5670 and ov5693.
>>
>> Adding a new sensor is pretty straightforward as one only needs to
>> implement the sub-class for it and register that class to the
>> CameraSensorHelperFactory.
> 
> While extending the factories to add a new class seems simple, I'm
> having a hard time to determine what the 'correct' way to extend it is.
> 
> How would I determine the correct values for each of the fields for
> instance?
> 
> Is there any guidance on where this information comes from or how it
> should be determined? or are they values you already had somewhere?
> 
> For instance, we now need to add the ov13858, which is on the Soraka.
> 
> What should we follow to add that ?

You need to determine the model used on your sensor (Linear or
Exponential, or something else :-)).
In case of imx219, the datasheet explicitly gives the m0/m1 and c0/c1
values, so it is easy :-).
In OV5693, the datasheet mentions a *16 gain so the parameters are
defined to have gainCode = 16 * gain / 1.

> 
> I've added defaults by copying another as an example, but that's no
> different to us supplying incorrect defaults otherwise.
> 
> I think outright failure when this data isn't provided is a better
> option here though (which is what has happened to me), as it forces the
> user to find out how to get the right values, and make sure they are
> added - but the easier it is to demonstrate how to do that correctly,
> the better.
> 
> --
> Kieran
> 
> 
>>
>> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
>> Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
>> ---
>>  src/ipa/libipa/camera_sensor_helper.cpp | 318 ++++++++++++++++++++++++
>>  src/ipa/libipa/camera_sensor_helper.h   |  87 +++++++
>>  src/ipa/libipa/meson.build              |   2 +
>>  3 files changed, 407 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..a114ee73
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.cpp
>> @@ -0,0 +1,318 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.cpp - Helper class that performs sensor-specific parameter computations
>> + */
>> +#include "camera_sensor_helper.h"
>> +
>> +#include "libcamera/internal/log.h"
>> +
>> +/**
>> + * \file camera_sensor_helper.h
>> + * \brief Helper class that performs sensor-specific parameter computations
>> + *
>> + * Computation of sensor configuration parameters is a sensor specific
>> + * operation. Each CameraHelper derived class computes the value of
>> + * configuration parameters, for example the analogue gain value, using
>> + * sensor-specific functions and constants.
>> + *
>> + * 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 Base class for computing sensor tuning parameters using sensor-specific constants
>> + *
>> + * CameraSensorHelper derived class instances are sensor specific. Each
>> + * supported sensor will have an associated base class defined.
>> + */
>> +
>> +/**
>> + * \brief Construct a CameraSensorHelper instance
>> + *
>> + * CameraSensorHelper derived class instances shall never be constructed manually
>> + * but always through the CameraSensorHelperFactory::create() method.
>> + */
>> +
>> +/**
>> + * \brief Compute gain code from the analogue gain absolute 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).
>> + *
>> + * \return The gain code to pass to V4l2
>> + */
>> +uint32_t CameraSensorHelper::gainCode(double gain) const
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +	return (analogueGainConstants_.c0 - analogueGainConstants_.c1 * gain) /
>> +	       (analogueGainConstants_.m1 * gain - analogueGainConstants_.m0);
>> +}
>> +
>> +/**
>> + * \brief Compute the real gain from the V4l2 subdev control gain code
>> + * \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::gainCode.
>> + *
>> + * The parameters come from the MIPI Alliance Camera Specification for
>> + * Camera Command Set (CCS).
>> + *
>> + * \return The real gain
>> + */
>> +double CameraSensorHelper::gain(uint32_t gainCode) const
>> +{
>> +	ASSERT((analogueGainConstants_.m0 == 0) || (analogueGainConstants_.m1 == 0));
>> +	ASSERT(analogueGainConstants_.type == AnalogueGainLinear);
>> +
>> +	return (analogueGainConstants_.m0 * static_cast<double>(gainCode) + analogueGainConstants_.c0) /
>> +	       (analogueGainConstants_.m1 * static_cast<double>(gainCode) + analogueGainConstants_.c1);
>> +}
>> +
>> +/**
>> + * \enum CameraSensorHelper::AnalogueGainType
>> + * \brief the gain calculation modes as defined by the MIPI CCS
>> + *
>> + * Describes the image sensor analogue gain capabilities.
>> + * Two modes are possible, depending on the sensor: Global and Alternate.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainLinear
>> + * \brief Gain is computed using linear gain estimation
>> + *
>> + * The relationship between the integer gain parameter and the resulting gain
>> + * multiplier is given by the following equation:
>> + *
>> + * \f$gain=\frac{m0x+c0}{m1x+c1}\f$
>> + *
>> + * Where 'x' is the gain control parameter, and m0, m1, c0 and c1 are
>> + * image-sensor-specific constants of 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$gain=\frac{c0}{m1x+c1}\f$ or \f$\frac{m0x+c0}{c1}\f$
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainExponential
>> + * \brief Gain is computed using exponential gain estimation (introduced in CCS v1.1)
>> + *
>> + * Starting with CCS v1.1, Alternate Global Analogue Gain is also available.
>> + * If the image sensor supports it, then the global analogue 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 calculation mode
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m0
>> + * \brief Constant used in the analogue Gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c0
>> + * \brief Constant used in the analogue gain coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::m1
>> + * \brief Constant used in the analogue gain coding/decoding
>> + *
>> + * \note either m0 or m1 shall be zero.
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::AnalogueGainConstants::c1
>> + * \brief Constant used in the analogue gain coding/decoding
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelper::analogueGainConstants_
>> + * \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 std::string name)
>> +	: name_(name)
>> +{
>> +	registerType(this);
>> +}
>> +
>> +/**
>> + * \brief Create an instance of the CameraSensorHelper corresponding to the factory
>> + * \param[in] name Name of the factory
>> + *
>> + * \return A unique pointer to a new instance of the CameraSensorHelper subclass
>> + * corresponding to the factory
>> + */
>> +std::unique_ptr<CameraSensorHelper> CameraSensorHelperFactory::create(const std::string &name)
>> +{
>> +	std::vector<CameraSensorHelperFactory *> &factories =
>> +		CameraSensorHelperFactory::factories();
>> +
>> +	for (CameraSensorHelperFactory *factory : factories) {
>> +		if (name != factory->name_)
>> +			continue;
>> +
>> +		CameraSensorHelper *helper = factory->createInstance();
>> +		return std::unique_ptr<CameraSensorHelper>(helper);
>> +	}
>> +
>> +	return nullptr;
>> +}
>> +
>> +/**
>> + * \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
>> + */
>> +
>> +/**
>> + * \var CameraSensorHelperFactory::name_
>> + * \brief The name of 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] helper 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
>> + */
>> +class CameraSensorHelperImx219 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperImx219()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 0, -1, 256, 256 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("imx219", CameraSensorHelperImx219)
>> +
>> +/**
>> + * \class CameraSensorHelperOv5670
>> + * \brief Create and give helpers for the ov5670 sensor
>> + */
>> +class CameraSensorHelperOv5670 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperOv5670()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 256 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5670", CameraSensorHelperOv5670)
>> +
>> +/**
>> + * \class CameraSensorHelperOv5693
>> + * \brief Create and give helpers for the ov5693 sensor
>> + */
>> +class CameraSensorHelperOv5693 : public CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelperOv5693()
>> +	{
>> +		analogueGainConstants_ = { AnalogueGainLinear, 1, 0, 0, 16 };
>> +	}
>> +};
>> +REGISTER_CAMERA_SENSOR_HELPER("ov5693", CameraSensorHelperOv5693)
>> +
>> +} /* 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..c43e4bf6
>> --- /dev/null
>> +++ b/src/ipa/libipa/camera_sensor_helper.h
>> @@ -0,0 +1,87 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2021, Google Inc.
>> + *
>> + * camera_sensor_helper.h - Helper class that performs sensor-specific parameter computations
>> + */
>> +#ifndef __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +#define __LIBCAMERA_IPA_LIBIPA_CAMERA_SENSOR_HELPER_H__
>> +
>> +#include <stdint.h>
>> +
>> +#include <memory>
>> +#include <string>
>> +#include <vector>
>> +
>> +#include <libcamera/class.h>
>> +
>> +namespace libcamera {
>> +
>> +namespace ipa {
>> +
>> +class CameraSensorHelper
>> +{
>> +public:
>> +	CameraSensorHelper() = default;
>> +	virtual ~CameraSensorHelper() = default;
>> +
>> +	virtual uint32_t gainCode(double gain) const;
>> +	virtual double gain(uint32_t gainCode) const;
>> +
>> +protected:
>> +	enum AnalogueGainType {
>> +		AnalogueGainLinear = 0,
>> +		AnalogueGainExponential = 2,
>> +	};
>> +
>> +	struct AnalogueGainConstants {
>> +		AnalogueGainType type;
>> +		int16_t m0;
>> +		int16_t c0;
>> +		int16_t m1;
>> +		int16_t c1;
>> +	};
>> +
>> +	AnalogueGainConstants analogueGainConstants_;
>> +
>> +private:
>> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelper)
>> +};
>> +
>> +class CameraSensorHelperFactory
>> +{
>> +public:
>> +	CameraSensorHelperFactory(const std::string name);
>> +	virtual ~CameraSensorHelperFactory() = default;
>> +
>> +	static std::unique_ptr<CameraSensorHelper> create(const std::string &name);
>> +
>> +	static void registerType(CameraSensorHelperFactory *factory);
>> +	static std::vector<CameraSensorHelperFactory *> &factories();
>> +
>> +protected:
>> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(CameraSensorHelperFactory)
>> +	virtual CameraSensorHelper *createInstance() = 0;
>> +
>> +	std::string name_;
>> +};
>> +
>> +#define REGISTER_CAMERA_SENSOR_HELPER(name, helper)		  \
>> +class helper##Factory final : public CameraSensorHelperFactory	  \
>> +{                                                                 \
>> +public:                                                           \
>> +	helper##Factory() : CameraSensorHelperFactory(name) {}	  \
>> +								  \
>> +private:                                                          \
>> +	CameraSensorHelper *createInstance()			  \
>> +	{							  \
>> +		return new helper();				  \
>> +	}							  \
>> +};								  \
>> +static helper##Factory global_##helper##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'
>>  ])
>>  
>>