[libcamera-devel,1/2] libcamera: Declare generic converter interface

17568 diff mbox series

From: Xavier Roumegue <xavier.roumegue@oss.nxp.com>

Declare a converter Abstract Base Class intended to provide generic
interfaces to hardware offering size and format conversion services on
streams. This is mainly based on the public interfaces of the current
converter class implementation found in the simple pipeline handler.

The main change is the introduction of loadConfiguration() function
which can be used by the concrete implementation to load hardware
specific runtime parameters defined by the application.

Signed-off-by: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
---
 include/libcamera/internal/converter.h | 108 ++++++++
 include/libcamera/internal/meson.build |   1 +
 src/libcamera/converter.cpp            | 337 +++++++++++++++++++++++++
 src/libcamera/meson.build              |   1 +
 4 files changed, 447 insertions(+)
 create mode 100644 include/libcamera/internal/converter.h
 create mode 100644 src/libcamera/converter.cpp

HI Xavier,
  sorry for the delay!

On Mon, Oct 10, 2022 at 03:17:43PM +0200, Xavier Roumegue (OSS) wrote:
> From: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
>
> Declare a converter Abstract Base Class intended to provide generic
> interfaces to hardware offering size and format conversion services on
> streams. This is mainly based on the public interfaces of the current
> converter class implementation found in the simple pipeline handler.
>
> The main change is the introduction of loadConfiguration() function
> which can be used by the concrete implementation to load hardware
> specific runtime parameters defined by the application.
>
> Signed-off-by: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
> ---
>  include/libcamera/internal/converter.h | 108 ++++++++
>  include/libcamera/internal/meson.build |   1 +
>  src/libcamera/converter.cpp            | 337 +++++++++++++++++++++++++
>  src/libcamera/meson.build              |   1 +
>  4 files changed, 447 insertions(+)
>  create mode 100644 include/libcamera/internal/converter.h
>  create mode 100644 src/libcamera/converter.cpp
>
> diff --git a/include/libcamera/internal/converter.h b/include/libcamera/internal/converter.h
> new file mode 100644
> index 00000000..38c05ee9
> --- /dev/null
> +++ b/include/libcamera/internal/converter.h
> @@ -0,0 +1,108 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2020, Laurent Pinchart
> + * Copyright 2022 NXP
> + *
> + * converter.h - Generic stream converter infrastructure

Please align this with the .cpp one. Pick the one that you prefer

 * converter.h - Generic stream converter infrastructure
 * converter.cpp - Generic Format converter interface


> + */
> +
> +#pragma once
> +
> +#include <map>
> +#include <memory>

#include <initializer_list>

> +#include <string>
> +#include <tuple>
> +#include <vector>
> +
> +#include <libcamera/base/class.h>
> +#include <libcamera/base/signal.h>
> +
> +#include <libcamera/geometry.h>
> +#include <libcamera/pixel_format.h>
> +
> +namespace libcamera {
> +
> +class FrameBuffer;
> +class MediaDevice;
> +class Size;
> +class SizeRange;
> +struct StreamConfiguration;
> +
> +class Converter
> +{
> +public:
> +	Converter(MediaDevice *media);
> +	virtual ~Converter();
> +
> +	virtual int loadConfiguration(const std::string &filename) = 0;
> +
> +	virtual bool isValid() const = 0;
> +
> +	virtual std::vector<PixelFormat> formats(PixelFormat input) = 0;
> +	virtual SizeRange sizes(const Size &input) = 0;
> +
> +	virtual std::tuple<unsigned int, unsigned int>
> +	strideAndFrameSize(const PixelFormat &pixelFormat, const Size &size) = 0;
> +
> +	virtual int configure(const StreamConfiguration &inputCfg,
> +			      const std::vector<std::reference_wrapper<StreamConfiguration>> &outputCfg) = 0;

I wonder if using <StreamConfiguration *> would be easier than
reference_wrapper, but I'll find out in the next patch I presume

> +	virtual int exportBuffers(unsigned int ouput, unsigned int count,
> +				  std::vector<std::unique_ptr<FrameBuffer>> *buffers) = 0;
> +
> +	virtual int start() = 0;
> +	virtual void stop() = 0;
> +
> +	virtual int queueBuffers(FrameBuffer *input,
> +				 const std::map<unsigned int, FrameBuffer *> &outputs) = 0;
> +
> +	Signal<FrameBuffer *> inputBufferReady;
> +	Signal<FrameBuffer *> outputBufferReady;
> +
> +	const std::string &deviceNode() const { return deviceNode_; };
> +
> +private:
> +	std::string deviceNode_;
> +};
> +
> +class ConverterFactoryBase
> +{
> +public:
> +	ConverterFactoryBase(const std::string name, std::initializer_list<std::string> aliases);
> +	virtual ~ConverterFactoryBase() = default;
> +
> +	const std::vector<std::string> &aliases() const { return aliases_; }
> +
> +	static std::unique_ptr<Converter> create(MediaDevice *media);
> +	static std::vector<ConverterFactoryBase *> &factories();
> +	static std::vector<std::string> names();
> +
> +private:
> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(ConverterFactoryBase)
> +
> +	static void registerType(ConverterFactoryBase *factory);
> +
> +	virtual std::unique_ptr<Converter> createInstance(MediaDevice *media) const = 0;
> +
> +	std::string name_;
> +	std::vector<std::string> aliases_;
> +};
> +
> +template<typename _Converter>
> +class ConverterFactory : public ConverterFactoryBase
> +{
> +public:
> +	ConverterFactory(const char *name, std::initializer_list<std::string> aliases)
> +		: ConverterFactoryBase(name, aliases)
> +	{
> +	}
> +
> +	std::unique_ptr<Converter> createInstance(MediaDevice *media) const override
> +	{
> +		return std::make_unique<_Converter>(media);
> +	}
> +};
> +
> +#define REGISTER_CONVERTER(name, converter, ...) \
> +	static ConverterFactory<converter> global_##converter##Factory(name, { __VA_ARGS__ });
> +
> +} /* namespace libcamera */
> diff --git a/include/libcamera/internal/meson.build b/include/libcamera/internal/meson.build
> index 7a780d48..8f50d755 100644
> --- a/include/libcamera/internal/meson.build
> +++ b/include/libcamera/internal/meson.build
> @@ -19,6 +19,7 @@ libcamera_internal_headers = files([
>      'camera_sensor_properties.h',
>      'control_serializer.h',
>      'control_validator.h',
> +    'converter.h',
>      'delayed_controls.h',
>      'device_enumerator.h',
>      'device_enumerator_sysfs.h',
> diff --git a/src/libcamera/converter.cpp b/src/libcamera/converter.cpp
> new file mode 100644
> index 00000000..5e444f5f
> --- /dev/null
> +++ b/src/libcamera/converter.cpp

I get quite a few Doxygen warnings on this class

src/libcamera/converter.cpp:328: warning: argument 'aliases' of command @param is not found in the argument list of REGISTER_CONVERTER(name, converter,...)
src/libcamera/converter.cpp:113: warning: argument 'output' of command @param is not found in the argument list of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0
include/libcamera/internal/converter.h:49: warning: The following parameter of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0 is not documented:
  parameter 'ouput'
src/libcamera/converter.cpp:139: warning: argument 'buffers' of command @param is not found in the argument list of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0
include/libcamera/internal/converter.h:55: warning: The following parameter of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0 is not documented:
  parameter 'outputs'
include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
include/libcamera/internal/converter.h:70: warning: The following parameter of libcamera::ConverterFactoryBase::ConverterFactoryBase(const std::string name, std::initializer_list< std::string > aliases) is not documented:
  parameter 'aliases'
src/libcamera/converter.cpp:199: warning: argument 'name' of command @param is not found in the argument list of libcamera::ConverterFactoryBase::create(MediaDevice *media)
include/libcamera/internal/converter.h:75: warning: The following parameter of libcamera::ConverterFactoryBase::create(MediaDevice *media) is not documented:
  parameter 'media'


With the next patch applied the list increases:


src/libcamera/converter.cpp:328: warning: argument 'aliases' of command @param is not found in the argument list of REGISTER_CONVERTER(name, converter,...)
src/libcamera/converter.cpp:113: warning: argument 'output' of command @param is not found in the argument list of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0
include/libcamera/internal/converter.h:49: warning: The following parameter of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0 is not documented:
  parameter 'ouput'
src/libcamera/converter.cpp:139: warning: argument 'buffers' of command @param is not found in the argument list of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0
include/libcamera/internal/converter.h:55: warning: The following parameter of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0 is not documented:
  parameter 'outputs'
include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
include/libcamera/internal/converter.h:70: warning: The following parameter of libcamera::ConverterFactoryBase::ConverterFactoryBase(const std::string name, std::initializer_list< std::string > aliases) is not documented:
  parameter 'aliases'
src/libcamera/converter.cpp:199: warning: argument 'name' of command @param is not found in the argument list of libcamera::ConverterFactoryBase::create(MediaDevice *media)
include/libcamera/internal/converter.h:75: warning: The following parameter of libcamera::ConverterFactoryBase::create(MediaDevice *media) is not documented:
  parameter 'media'
src/libcamera/converter/converter_v4l2_m2m.cpp:323: warning: argument 'outputCfg' of command @param is not found in the argument list of libcamera::V4L2M2MConverter::configure(const StreamConfiguration &inputCfg, const std::vector< std::reference_wrapper< StreamConfiguration >> &outputCfgs)
include/libcamera/internal/converter/converter_v4l2_m2m.h:48: warning: The following parameter of libcamera::V4L2M2MConverter::configure(const StreamConfiguration &inputCfg, const std::vector< std::reference_wrapper< StreamConfiguration >> &outputCfgs) is not documented:
  parameter 'outputCfgs'
src/libcamera/converter/converter_v4l2_m2m.cpp:217: warning: argument 'filename' of command @param is not found in the argument list of libcamera::V4L2M2MConverter::formats(PixelFormat input)
src/libcamera/converter/converter_v4l2_m2m.cpp:396: warning: argument 'buffers' of command @param is not found in the argument list of libcamera::V4L2M2MConverter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)
include/libcamera/internal/converter/converter_v4l2_m2m.h:56: warning: The following parameter of libcamera::V4L2M2MConverter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs) is not documented:  parameter 'outputs'

Could you make sure Doxygen doesn't report any warning ?

> @@ -0,0 +1,337 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright 2022 NXP
> + *
> + * converter.cpp - Generic Format converter interface
> + */
> +
> +#include "libcamera/internal/converter.h"
> +
> +#include <algorithm>
> +
> +#include <libcamera/base/log.h>
> +
> +#include "libcamera/internal/media_device.h"
> +
> +/**
> + * \file internal/converter.h
> + * \brief Abstract converter
> + */
> +
> +namespace libcamera {
> +
> +LOG_DEFINE_CATEGORY(Converter)
> +
> +/**
> + * \class Converter
> + * \brief Abstract Base Class for converter
> + *
> + * The Converter class is an Abstract Base Class defining the interfaces of
> + * converter implementations.
> + *
> + * Converters offers scaling and pixel formats conversion services on a input

Converters -> offer

I would also use "pixel format" in singular form, but I can't tell if
that's more correct or not.


> + * stream. The converter can output multiple streams with individual conversion
> + * parameters from the same input stream.
> + */
> +
> +/**
> + * \brief Construct a Converter instance
> + * \param[in] media The media device implementing the converter
> + *
> + * This seeks for the entity implementing data streaming function in the media
> + * graph entities and use its device node as converter device node.
> + */
> +Converter::Converter(MediaDevice *media)
> +{
> +	const std::vector<MediaEntity *> &entities = media->entities();
> +	auto it = std::find_if(entities.begin(), entities.end(),
> +			       [](MediaEntity *entity) {
> +				       return entity->function() == MEDIA_ENT_F_IO_V4L;
> +			       });
> +	if (it == entities.end()) {
> +		LOG(Converter, Error)
> +			<< "No entity suitable for implementing a converter in "
> +			<< media->driver() << " entities list.";
> +		return;
> +	}
> +
> +	deviceNode_ = (*it)->deviceNode();
> +}
> +
> +Converter::~Converter()
> +{
> +}
> +
> +/**
> + * \fn Converter::loadConfiguration()
> + * \brief Load converter configuration from file
> + * \param[in] filename The file name path
> + *
> + * Load converter dependent configuration parameters to apply on the hardware.
> + *
> + * \return 0 on success or a negative error code otherwise
> + */
> +
> +/**
> + * \fn Converter::isValid()
> + * \brief Check if the converter configuration is valid
> + * \return True is the converter is valid, false otherwise
> + */
> +
> +/**
> + * \fn Converter::formats()
> + * \brief Retrieve the list of supported pixel formats for an input pixel format
> + * \param[in] input Input pixel format to retrieve output pixel format list for
> + * \return The list of output supported pixel formats

I would swap "output supported" to "supported output"

> + */
> +
> +/**
> + * \fn Converter::sizes()
> + * \brief Retrieve the output range of minimum and maximum sizes for an input size

Here too: "range of minimum and maximum output sizes"

> + * \param[in] input Input stream size to retrieve range for
> + * \return A range of output image sizes
> + */
> +
> +/**
> + * \fn Converter::strideAndFrameSize()
> + * \brief Retrieve the output stride and frame size for an input configutation
> + * \param[in] pixelFormat Input stream pixel format
> + * \param[in] size Input stream size
> + * \return A tuple indicating the stride and frame size or an empty tuple on error
> + */
> +
> +/**
> + * \fn Converter::configure()
> + * \brief Configure a set of output stream conversion from an input stream
> + * \param[in] inputCfg Input stream configuration
> + * \param[in] outputCfg A list of output stream configurations

Is this an [out] parameter ?

> + * \return 0 on success or a negative error code otherwise
> + */
> +
> +/**
> + * \fn Converter::exportBuffers()
> + * \brief Export buffers from the converter device
> + * \param[in] output Output stream index exporting the buffers
> + * \param[in] count Number of buffers to allocate
> + * \param[out] buffers Vector to store allocated buffers
> + *
> + * This function operates similarly as V4L2VideoDevice::exportBuffers() on the
> + * output stream indicated by the \a output index.
> + *
> + * \return The number of allocated buffers on success or a negative error code
> + * otherwise
> + */
> +
> +/**
> + * \fn Converter::start()
> + * \brief Start the converter streaming operation
> + * \return 0 on success or a negative error code otherwise
> + */
> +
> +/**
> + * \fn Converter::stop()
> + * \brief Stop the converter streaming operation
> + * \return 0 on success or a negative error code otherwise
> + */
> +
> +/**
> + * \fn Converter::queueBuffers()
> + * \brief Queue buffers to converter device
> + * \param[in] input The frame buffer to apply the conversion
> + * \param[out] buffers The container holding the output stream indexes and
> + * their respective frame buffer outputs.
> + *
> + * This function queues the \a input frame buffer on the output streams of the
> + * \a buffers map key and retrieve the output frame buffer indicated by the
> + * \a buffer map value.

"buffer" is not an argument. Maybe "buffers".

I'll better understand how the output map is populated in the next
patch

> + *
> + * \return 0 on success or a negative error code otherwise
> + */
> +
> +/**
> + * \var Converter::inputBufferReady
> + * \brief A signal emitted when the input frame buffer completes
> + */
> +
> +/**
> + * \var Converter::outputBufferReady
> + * \brief A signal emitted when the output frame buffer completes
> + */
> +
> +/**
> + * \fn Converter::deviceNode()
> + * \brief The converter device node attribute accessor
> + * \return The converter device node string
> + */
> +
> +/**
> + * \class ConverterFactoryBase
> + * \brief Base class for converter factories
> + *
> + * The ConverterFactoryBase class is the base of all specializations of the
> + * ConverterFactory class template. It implements the factory registration,
> + * maintains a registry of factories, and provides access to the registered
> + * factories.
> + */
> +
> +/**
> + * \brief Construct a converter factory base
> + * \param[in] name Name of the converter class
> + *
> + * Creating an instance of the factory base registers it with the global list of
> + * factories, accessible through the factories() function.
> + *
> + * The factory \a name is used as unique identifier.

Please don't break lines in paragraphs.

Either
      One line.

      With a line break in between.

Or
      One sentence. And the paragraph continues without breaking.

> + * If the converter implemententation fully relies on a generic framework, the
> + * name should be the same as the framework.
> + * Otherwise, if the implementation is specialized, the factory name should match
> + * the driver name implementing the function.
> + * The factory \a aliases holds a list of driver names implementing a generic
> + * subsystem without any personalizations.
> + */
> +ConverterFactoryBase::ConverterFactoryBase(const std::string name, std::initializer_list<std::string> aliases)
> +	: name_(name), aliases_(aliases)
> +{
> +	registerType(this);
> +}
> +
> +/**
> + * \brief Create an instance of the converter corresponding to a named factory
> + * \param[in] name Name of the factory
> + *
> + * \return A unique pointer to a new instance of the converter subclass
> + * corresponding to the named factory or one of its alias. Otherwise a null
> + * pointer if no such factory exists
> + */
> +std::unique_ptr<Converter> ConverterFactoryBase::create(MediaDevice *media)
> +{
> +	const std::vector<ConverterFactoryBase *> &factories =
> +		ConverterFactoryBase::factories();
> +
> +	for (const ConverterFactoryBase *factory : factories) {
> +		std::vector<std::string> aliases = factory->aliases();

                                        &aliases

> +		auto it = std::find(aliases.begin(), aliases.end(), media->driver());
> +
> +		if (it == aliases.end() && media->driver() != factory->name_)
> +			continue;
> +
> +		LOG(Converter, Debug)
> +			<< "Creating converter from "
> +			<< factory->name_ << " factory with "
> +			<< (it == aliases.end() ? "no" : media->driver()) << " alias.";
> +
> +		return factory->createInstance(media);
> +	}
> +
> +	return nullptr;
> +}
> +
> +/**
> + * \brief Add a converter class to the registry
> + * \param[in] factory Factory to use to construct the converter class
> + *
> + * The caller is responsible to guarantee the uniqueness of the converter name.
> + */
> +void ConverterFactoryBase::registerType(ConverterFactoryBase *factory)
> +{
> +	std::vector<ConverterFactoryBase *> &factories =
> +		ConverterFactoryBase::factories();
> +
> +	factories.push_back(factory);
> +}
> +
> +/**
> + * \brief Retrieve the list of all converter factory names
> + * \return The list of all converter factory names
> + */
> +std::vector<std::string> ConverterFactoryBase::names()

What is this function for ? Return the names of all converters
registered in the system ? Am I missing where it is used ?

> +{
> +	std::vector<std::string> list;
> +
> +	std::vector<ConverterFactoryBase *> &factories =
> +		ConverterFactoryBase::factories();
> +
> +	for (ConverterFactoryBase *factory : factories) {
> +		list.push_back(factory->name_);
> +		for (auto alias : factory->aliases())
> +			list.push_back(alias);
> +	}
> +
> +	return list;
> +}
> +
> +/**
> + * \brief Retrieve the list of all converter factories
> + * \return The list of converter factories
> + */
> +std::vector<ConverterFactoryBase *> &ConverterFactoryBase::factories()
> +{
> +	/*
> +	 * The static factories map is defined inside the function to ensure
> +	 * it gets initialized on first use, without any dependency on link
> +	 * order.
> +	 */
> +	static std::vector<ConverterFactoryBase *> factories;
> +	return factories;
> +}
> +
> +/**
> + * \var ConverterFactoryBase::name_
> + * \brief The name of the factory
> + */
> +
> +/**
> + * \var ConverterFactoryBase::aliases_
> + * \brief The list holding the factory aliases
> + */
> +
> +/**
> + * \class ConverterFactory
> + * \brief Registration of ConverterFactory classes and creation of instances
> + * \param _Converter The converter class type for this factory
> + *
> + * To facilitate discovery and instantiation of Converter classes, the
> + * ConverterFactory class implements auto-registration of converter helpers.
> + * Each Converter subclass shall register itself using the REGISTER_CONVERTER()
> + * macro, which will create a corresponding instance of a ConverterFactory
> + * subclass and register it with the static list of factories.
> + */
> +
> +/**
> + * \fn ConverterFactory::ConverterFactory(const char *name, std::initializer_list<std::string> aliases)
> + * \brief Construct a converter factory
> + * \param[in] name Name of the converter class
> + * \param[in] aliases Aliases of the converter 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 as unique identifier.
> + * If the converter implemententation fully relies on a generic framework, the
> + * name should be the same as the framework.
> + * Otherwise, if the implementation is specialized, the factory name should match
> + * the driver name implementing the function.
> + * The factory \a aliases holds a list of driver names implementing a generic
> + * subsystem without any personalizations.

Same comment as above.
Also, you can use \copydoc

> + */
> +
> +/**
> + * \fn ConverterFactory::createInstance() const
> + * \brief Create an instance of the Converter corresponding to the factory
> + * \param[in] media Media device pointer
> + * \return A unique pointer to a newly constructed instance of the Converter
> + * subclass corresponding to the factory
> + */
> +
> +/**
> + * \def REGISTER_CONVERTER
> + * \brief Register a converter with the Converter factory
> + * \param[in] name Converter name used to register the class
> + * \param[in] converter Class name of Converter derived class to register
> + * \param[in] aliases Optional list of alias names
> + *
> + * Register a Converter subclass with the factory and make it available to try
> + * and match converters.
> + */
> +
> +} /* namespace libcamera */
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index 7fcbb2dd..3a9fc31f 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -13,6 +13,7 @@ libcamera_sources = files([
>      'controls.cpp',
>      'control_serializer.cpp',
>      'control_validator.cpp',
> +    'converter.cpp',
>      'delayed_controls.cpp',
>      'device_enumerator.cpp',
>      'device_enumerator_sysfs.cpp',
> --
> 2.37.3
>

Hi Jacopo,

On 11/9/22 08:43, Jacopo Mondi wrote:
> HI Xavier,
>    sorry for the delay!
> 
> On Mon, Oct 10, 2022 at 03:17:43PM +0200, Xavier Roumegue (OSS) wrote:
>> From: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
>>
>> Declare a converter Abstract Base Class intended to provide generic
>> interfaces to hardware offering size and format conversion services on
>> streams. This is mainly based on the public interfaces of the current
>> converter class implementation found in the simple pipeline handler.
>>
>> The main change is the introduction of loadConfiguration() function
>> which can be used by the concrete implementation to load hardware
>> specific runtime parameters defined by the application.
>>
>> Signed-off-by: Xavier Roumegue <xavier.roumegue@oss.nxp.com>
>> ---
>>   include/libcamera/internal/converter.h | 108 ++++++++
>>   include/libcamera/internal/meson.build |   1 +
>>   src/libcamera/converter.cpp            | 337 +++++++++++++++++++++++++
>>   src/libcamera/meson.build              |   1 +
>>   4 files changed, 447 insertions(+)
>>   create mode 100644 include/libcamera/internal/converter.h
>>   create mode 100644 src/libcamera/converter.cpp
>>
>> diff --git a/include/libcamera/internal/converter.h b/include/libcamera/internal/converter.h
>> new file mode 100644
>> index 00000000..38c05ee9
>> --- /dev/null
>> +++ b/include/libcamera/internal/converter.h
>> @@ -0,0 +1,108 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright (C) 2020, Laurent Pinchart
>> + * Copyright 2022 NXP
>> + *
>> + * converter.h - Generic stream converter infrastructure
> 
> Please align this with the .cpp one. Pick the one that you prefer
> 
>   * converter.h - Generic stream converter infrastructure
>   * converter.cpp - Generic Format converter interface
> 
> 
>> + */
>> +
>> +#pragma once
>> +
>> +#include <map>
>> +#include <memory>
> 
> #include <initializer_list>
> 
>> +#include <string>
>> +#include <tuple>
>> +#include <vector>
>> +
>> +#include <libcamera/base/class.h>
>> +#include <libcamera/base/signal.h>
>> +
>> +#include <libcamera/geometry.h>
>> +#include <libcamera/pixel_format.h>
>> +
>> +namespace libcamera {
>> +
>> +class FrameBuffer;
>> +class MediaDevice;
>> +class Size;
>> +class SizeRange;
>> +struct StreamConfiguration;
>> +
>> +class Converter
>> +{
>> +public:
>> +	Converter(MediaDevice *media);
>> +	virtual ~Converter();
>> +
>> +	virtual int loadConfiguration(const std::string &filename) = 0;
>> +
>> +	virtual bool isValid() const = 0;
>> +
>> +	virtual std::vector<PixelFormat> formats(PixelFormat input) = 0;
>> +	virtual SizeRange sizes(const Size &input) = 0;
>> +
>> +	virtual std::tuple<unsigned int, unsigned int>
>> +	strideAndFrameSize(const PixelFormat &pixelFormat, const Size &size) = 0;
>> +
>> +	virtual int configure(const StreamConfiguration &inputCfg,
>> +			      const std::vector<std::reference_wrapper<StreamConfiguration>> &outputCfg) = 0;
> 
> I wonder if using <StreamConfiguration *> would be easier than
> reference_wrapper, but I'll find out in the next patch I presume
> 
>> +	virtual int exportBuffers(unsigned int ouput, unsigned int count,
>> +				  std::vector<std::unique_ptr<FrameBuffer>> *buffers) = 0;
>> +
>> +	virtual int start() = 0;
>> +	virtual void stop() = 0;
>> +
>> +	virtual int queueBuffers(FrameBuffer *input,
>> +				 const std::map<unsigned int, FrameBuffer *> &outputs) = 0;
>> +
>> +	Signal<FrameBuffer *> inputBufferReady;
>> +	Signal<FrameBuffer *> outputBufferReady;
>> +
>> +	const std::string &deviceNode() const { return deviceNode_; };
>> +
>> +private:
>> +	std::string deviceNode_;
>> +};
>> +
>> +class ConverterFactoryBase
>> +{
>> +public:
>> +	ConverterFactoryBase(const std::string name, std::initializer_list<std::string> aliases);
>> +	virtual ~ConverterFactoryBase() = default;
>> +
>> +	const std::vector<std::string> &aliases() const { return aliases_; }
>> +
>> +	static std::unique_ptr<Converter> create(MediaDevice *media);
>> +	static std::vector<ConverterFactoryBase *> &factories();
>> +	static std::vector<std::string> names();
>> +
>> +private:
>> +	LIBCAMERA_DISABLE_COPY_AND_MOVE(ConverterFactoryBase)
>> +
>> +	static void registerType(ConverterFactoryBase *factory);
>> +
>> +	virtual std::unique_ptr<Converter> createInstance(MediaDevice *media) const = 0;
>> +
>> +	std::string name_;
>> +	std::vector<std::string> aliases_;
>> +};
>> +
>> +template<typename _Converter>
>> +class ConverterFactory : public ConverterFactoryBase
>> +{
>> +public:
>> +	ConverterFactory(const char *name, std::initializer_list<std::string> aliases)
>> +		: ConverterFactoryBase(name, aliases)
>> +	{
>> +	}
>> +
>> +	std::unique_ptr<Converter> createInstance(MediaDevice *media) const override
>> +	{
>> +		return std::make_unique<_Converter>(media);
>> +	}
>> +};
>> +
>> +#define REGISTER_CONVERTER(name, converter, ...) \
>> +	static ConverterFactory<converter> global_##converter##Factory(name, { __VA_ARGS__ });
>> +
>> +} /* namespace libcamera */
>> diff --git a/include/libcamera/internal/meson.build b/include/libcamera/internal/meson.build
>> index 7a780d48..8f50d755 100644
>> --- a/include/libcamera/internal/meson.build
>> +++ b/include/libcamera/internal/meson.build
>> @@ -19,6 +19,7 @@ libcamera_internal_headers = files([
>>       'camera_sensor_properties.h',
>>       'control_serializer.h',
>>       'control_validator.h',
>> +    'converter.h',
>>       'delayed_controls.h',
>>       'device_enumerator.h',
>>       'device_enumerator_sysfs.h',
>> diff --git a/src/libcamera/converter.cpp b/src/libcamera/converter.cpp
>> new file mode 100644
>> index 00000000..5e444f5f
>> --- /dev/null
>> +++ b/src/libcamera/converter.cpp
> 
> I get quite a few Doxygen warnings on this class
> 
> src/libcamera/converter.cpp:328: warning: argument 'aliases' of command @param is not found in the argument list of REGISTER_CONVERTER(name, converter,...)
> src/libcamera/converter.cpp:113: warning: argument 'output' of command @param is not found in the argument list of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0
> include/libcamera/internal/converter.h:49: warning: The following parameter of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0 is not documented:
>    parameter 'ouput'
> src/libcamera/converter.cpp:139: warning: argument 'buffers' of command @param is not found in the argument list of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0
> include/libcamera/internal/converter.h:55: warning: The following parameter of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0 is not documented:
>    parameter 'outputs'
> include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
> include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
> include/libcamera/internal/converter.h:70: warning: The following parameter of libcamera::ConverterFactoryBase::ConverterFactoryBase(const std::string name, std::initializer_list< std::string > aliases) is not documented:
>    parameter 'aliases'
> src/libcamera/converter.cpp:199: warning: argument 'name' of command @param is not found in the argument list of libcamera::ConverterFactoryBase::create(MediaDevice *media)
> include/libcamera/internal/converter.h:75: warning: The following parameter of libcamera::ConverterFactoryBase::create(MediaDevice *media) is not documented:
>    parameter 'media'
> 
> 
> With the next patch applied the list increases:
> 
> 
> src/libcamera/converter.cpp:328: warning: argument 'aliases' of command @param is not found in the argument list of REGISTER_CONVERTER(name, converter,...)
> src/libcamera/converter.cpp:113: warning: argument 'output' of command @param is not found in the argument list of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0
> include/libcamera/internal/converter.h:49: warning: The following parameter of libcamera::Converter::exportBuffers(unsigned int ouput, unsigned int count, std::vector< std::unique_ptr< FrameBuffer >> *buffers)=0 is not documented:
>    parameter 'ouput'
> src/libcamera/converter.cpp:139: warning: argument 'buffers' of command @param is not found in the argument list of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0
> include/libcamera/internal/converter.h:55: warning: The following parameter of libcamera::Converter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)=0 is not documented:
>    parameter 'outputs'
> include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
> include/libcamera/internal/converter.h:73: warning: Member aliases() const (function) of class libcamera::ConverterFactoryBase is not documented.
> include/libcamera/internal/converter.h:70: warning: The following parameter of libcamera::ConverterFactoryBase::ConverterFactoryBase(const std::string name, std::initializer_list< std::string > aliases) is not documented:
>    parameter 'aliases'
> src/libcamera/converter.cpp:199: warning: argument 'name' of command @param is not found in the argument list of libcamera::ConverterFactoryBase::create(MediaDevice *media)
> include/libcamera/internal/converter.h:75: warning: The following parameter of libcamera::ConverterFactoryBase::create(MediaDevice *media) is not documented:
>    parameter 'media'
> src/libcamera/converter/converter_v4l2_m2m.cpp:323: warning: argument 'outputCfg' of command @param is not found in the argument list of libcamera::V4L2M2MConverter::configure(const StreamConfiguration &inputCfg, const std::vector< std::reference_wrapper< StreamConfiguration >> &outputCfgs)
> include/libcamera/internal/converter/converter_v4l2_m2m.h:48: warning: The following parameter of libcamera::V4L2M2MConverter::configure(const StreamConfiguration &inputCfg, const std::vector< std::reference_wrapper< StreamConfiguration >> &outputCfgs) is not documented:
>    parameter 'outputCfgs'
> src/libcamera/converter/converter_v4l2_m2m.cpp:217: warning: argument 'filename' of command @param is not found in the argument list of libcamera::V4L2M2MConverter::formats(PixelFormat input)
> src/libcamera/converter/converter_v4l2_m2m.cpp:396: warning: argument 'buffers' of command @param is not found in the argument list of libcamera::V4L2M2MConverter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs)
> include/libcamera/internal/converter/converter_v4l2_m2m.h:56: warning: The following parameter of libcamera::V4L2M2MConverter::queueBuffers(FrameBuffer *input, const std::map< unsigned int, FrameBuffer * > &outputs) is not documented:  parameter 'outputs'
> 
> Could you make sure Doxygen doesn't report any warning ?
Fixed in v2.
> 
>> @@ -0,0 +1,337 @@
>> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
>> +/*
>> + * Copyright 2022 NXP
>> + *
>> + * converter.cpp - Generic Format converter interface
>> + */
>> +
>> +#include "libcamera/internal/converter.h"
>> +
>> +#include <algorithm>
>> +
>> +#include <libcamera/base/log.h>
>> +
>> +#include "libcamera/internal/media_device.h"
>> +
>> +/**
>> + * \file internal/converter.h
>> + * \brief Abstract converter
>> + */
>> +
>> +namespace libcamera {
>> +
>> +LOG_DEFINE_CATEGORY(Converter)
>> +
>> +/**
>> + * \class Converter
>> + * \brief Abstract Base Class for converter
>> + *
>> + * The Converter class is an Abstract Base Class defining the interfaces of
>> + * converter implementations.
>> + *
>> + * Converters offers scaling and pixel formats conversion services on a input
> 
> Converters -> offer
> 
> I would also use "pixel format" in singular form, but I can't tell if
> that's more correct or not.
> 
> 
>> + * stream. The converter can output multiple streams with individual conversion
>> + * parameters from the same input stream.
>> + */
>> +
>> +/**
>> + * \brief Construct a Converter instance
>> + * \param[in] media The media device implementing the converter
>> + *
>> + * This seeks for the entity implementing data streaming function in the media
>> + * graph entities and use its device node as converter device node.
>> + */
>> +Converter::Converter(MediaDevice *media)
>> +{
>> +	const std::vector<MediaEntity *> &entities = media->entities();
>> +	auto it = std::find_if(entities.begin(), entities.end(),
>> +			       [](MediaEntity *entity) {
>> +				       return entity->function() == MEDIA_ENT_F_IO_V4L;
>> +			       });
>> +	if (it == entities.end()) {
>> +		LOG(Converter, Error)
>> +			<< "No entity suitable for implementing a converter in "
>> +			<< media->driver() << " entities list.";
>> +		return;
>> +	}
>> +
>> +	deviceNode_ = (*it)->deviceNode();
>> +}
>> +
>> +Converter::~Converter()
>> +{
>> +}
>> +
>> +/**
>> + * \fn Converter::loadConfiguration()
>> + * \brief Load converter configuration from file
>> + * \param[in] filename The file name path
>> + *
>> + * Load converter dependent configuration parameters to apply on the hardware.
>> + *
>> + * \return 0 on success or a negative error code otherwise
>> + */
>> +
>> +/**
>> + * \fn Converter::isValid()
>> + * \brief Check if the converter configuration is valid
>> + * \return True is the converter is valid, false otherwise
>> + */
>> +
>> +/**
>> + * \fn Converter::formats()
>> + * \brief Retrieve the list of supported pixel formats for an input pixel format
>> + * \param[in] input Input pixel format to retrieve output pixel format list for
>> + * \return The list of output supported pixel formats
> 
> I would swap "output supported" to "supported output"
> 
>> + */
>> +
>> +/**
>> + * \fn Converter::sizes()
>> + * \brief Retrieve the output range of minimum and maximum sizes for an input size
> 
> Here too: "range of minimum and maximum output sizes"
> 
>> + * \param[in] input Input stream size to retrieve range for
>> + * \return A range of output image sizes
>> + */
>> +
>> +/**
>> + * \fn Converter::strideAndFrameSize()
>> + * \brief Retrieve the output stride and frame size for an input configutation
>> + * \param[in] pixelFormat Input stream pixel format
>> + * \param[in] size Input stream size
>> + * \return A tuple indicating the stride and frame size or an empty tuple on error
>> + */
>> +
>> +/**
>> + * \fn Converter::configure()
>> + * \brief Configure a set of output stream conversion from an input stream
>> + * \param[in] inputCfg Input stream configuration
>> + * \param[in] outputCfg A list of output stream configurations
> 
> Is this an [out] parameter ?
Yes, changed in v2
> 
>> + * \return 0 on success or a negative error code otherwise
>> + */
>> +
>> +/**
>> + * \fn Converter::exportBuffers()
>> + * \brief Export buffers from the converter device
>> + * \param[in] output Output stream index exporting the buffers
>> + * \param[in] count Number of buffers to allocate
>> + * \param[out] buffers Vector to store allocated buffers
>> + *
>> + * This function operates similarly as V4L2VideoDevice::exportBuffers() on the
>> + * output stream indicated by the \a output index.
>> + *
>> + * \return The number of allocated buffers on success or a negative error code
>> + * otherwise
>> + */
>> +
>> +/**
>> + * \fn Converter::start()
>> + * \brief Start the converter streaming operation
>> + * \return 0 on success or a negative error code otherwise
>> + */
>> +
>> +/**
>> + * \fn Converter::stop()
>> + * \brief Stop the converter streaming operation
>> + * \return 0 on success or a negative error code otherwise
>> + */
>> +
>> +/**
>> + * \fn Converter::queueBuffers()
>> + * \brief Queue buffers to converter device
>> + * \param[in] input The frame buffer to apply the conversion
>> + * \param[out] buffers The container holding the output stream indexes and
>> + * their respective frame buffer outputs.
>> + *
>> + * This function queues the \a input frame buffer on the output streams of the
>> + * \a buffers map key and retrieve the output frame buffer indicated by the
>> + * \a buffer map value.
> 
> "buffer" is not an argument. Maybe "buffers".
> 
> I'll better understand how the output map is populated in the next
> patch
> 
>> + *
>> + * \return 0 on success or a negative error code otherwise
>> + */
>> +
>> +/**
>> + * \var Converter::inputBufferReady
>> + * \brief A signal emitted when the input frame buffer completes
>> + */
>> +
>> +/**
>> + * \var Converter::outputBufferReady
>> + * \brief A signal emitted when the output frame buffer completes
>> + */
>> +
>> +/**
>> + * \fn Converter::deviceNode()
>> + * \brief The converter device node attribute accessor
>> + * \return The converter device node string
>> + */
>> +
>> +/**
>> + * \class ConverterFactoryBase
>> + * \brief Base class for converter factories
>> + *
>> + * The ConverterFactoryBase class is the base of all specializations of the
>> + * ConverterFactory class template. It implements the factory registration,
>> + * maintains a registry of factories, and provides access to the registered
>> + * factories.
>> + */
>> +
>> +/**
>> + * \brief Construct a converter factory base
>> + * \param[in] name Name of the converter class
>> + *
>> + * Creating an instance of the factory base registers it with the global list of
>> + * factories, accessible through the factories() function.
>> + *
>> + * The factory \a name is used as unique identifier.
> 
> Please don't break lines in paragraphs.
> 
> Either
>        One line.
> 
>        With a line break in between.
> 
> Or
>        One sentence. And the paragraph continues without breaking.
> 
>> + * If the converter implemententation fully relies on a generic framework, the
>> + * name should be the same as the framework.
>> + * Otherwise, if the implementation is specialized, the factory name should match
>> + * the driver name implementing the function.
>> + * The factory \a aliases holds a list of driver names implementing a generic
>> + * subsystem without any personalizations.
>> + */
>> +ConverterFactoryBase::ConverterFactoryBase(const std::string name, std::initializer_list<std::string> aliases)
>> +	: name_(name), aliases_(aliases)
>> +{
>> +	registerType(this);
>> +}
>> +
>> +/**
>> + * \brief Create an instance of the converter corresponding to a named factory
>> + * \param[in] name Name of the factory
>> + *
>> + * \return A unique pointer to a new instance of the converter subclass
>> + * corresponding to the named factory or one of its alias. Otherwise a null
>> + * pointer if no such factory exists
>> + */
>> +std::unique_ptr<Converter> ConverterFactoryBase::create(MediaDevice *media)
>> +{
>> +	const std::vector<ConverterFactoryBase *> &factories =
>> +		ConverterFactoryBase::factories();
>> +
>> +	for (const ConverterFactoryBase *factory : factories) {
>> +		std::vector<std::string> aliases = factory->aliases();
> 
>                                          &aliases
> 
>> +		auto it = std::find(aliases.begin(), aliases.end(), media->driver());
>> +
>> +		if (it == aliases.end() && media->driver() != factory->name_)
>> +			continue;
>> +
>> +		LOG(Converter, Debug)
>> +			<< "Creating converter from "
>> +			<< factory->name_ << " factory with "
>> +			<< (it == aliases.end() ? "no" : media->driver()) << " alias.";
>> +
>> +		return factory->createInstance(media);
>> +	}
>> +
>> +	return nullptr;
>> +}
>> +
>> +/**
>> + * \brief Add a converter class to the registry
>> + * \param[in] factory Factory to use to construct the converter class
>> + *
>> + * The caller is responsible to guarantee the uniqueness of the converter name.
>> + */
>> +void ConverterFactoryBase::registerType(ConverterFactoryBase *factory)
>> +{
>> +	std::vector<ConverterFactoryBase *> &factories =
>> +		ConverterFactoryBase::factories();
>> +
>> +	factories.push_back(factory);
>> +}
>> +
>> +/**
>> + * \brief Retrieve the list of all converter factory names
>> + * \return The list of all converter factory names
>> + */
>> +std::vector<std::string> ConverterFactoryBase::names()
> 
> What is this function for ? Return the names of all converters
> registered in the system ?
Yes.

  Am I missing where it is used ?
Currently not used but will be used in next series involving rkisp1 pipeline.
Pipeline handlers can retrieve a converter available in the system without 
hardcoding its name.
> 
>> +{
>> +	std::vector<std::string> list;
>> +
>> +	std::vector<ConverterFactoryBase *> &factories =
>> +		ConverterFactoryBase::factories();
>> +
>> +	for (ConverterFactoryBase *factory : factories) {
>> +		list.push_back(factory->name_);
>> +		for (auto alias : factory->aliases())
>> +			list.push_back(alias);
>> +	}
>> +
>> +	return list;
>> +}
>> +
>> +/**
>> + * \brief Retrieve the list of all converter factories
>> + * \return The list of converter factories
>> + */
>> +std::vector<ConverterFactoryBase *> &ConverterFactoryBase::factories()
>> +{
>> +	/*
>> +	 * The static factories map is defined inside the function to ensure
>> +	 * it gets initialized on first use, without any dependency on link
>> +	 * order.
>> +	 */
>> +	static std::vector<ConverterFactoryBase *> factories;
>> +	return factories;
>> +}
>> +
>> +/**
>> + * \var ConverterFactoryBase::name_
>> + * \brief The name of the factory
>> + */
>> +
>> +/**
>> + * \var ConverterFactoryBase::aliases_
>> + * \brief The list holding the factory aliases
>> + */
>> +
>> +/**
>> + * \class ConverterFactory
>> + * \brief Registration of ConverterFactory classes and creation of instances
>> + * \param _Converter The converter class type for this factory
>> + *
>> + * To facilitate discovery and instantiation of Converter classes, the
>> + * ConverterFactory class implements auto-registration of converter helpers.
>> + * Each Converter subclass shall register itself using the REGISTER_CONVERTER()
>> + * macro, which will create a corresponding instance of a ConverterFactory
>> + * subclass and register it with the static list of factories.
>> + */
>> +
>> +/**
>> + * \fn ConverterFactory::ConverterFactory(const char *name, std::initializer_list<std::string> aliases)
>> + * \brief Construct a converter factory
>> + * \param[in] name Name of the converter class
>> + * \param[in] aliases Aliases of the converter 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 as unique identifier.
>> + * If the converter implemententation fully relies on a generic framework, the
>> + * name should be the same as the framework.
>> + * Otherwise, if the implementation is specialized, the factory name should match
>> + * the driver name implementing the function.
>> + * The factory \a aliases holds a list of driver names implementing a generic
>> + * subsystem without any personalizations.
> 
> Same comment as above.
> Also, you can use \copydoc
> 
>> + */
>> +
>> +/**
>> + * \fn ConverterFactory::createInstance() const
>> + * \brief Create an instance of the Converter corresponding to the factory
>> + * \param[in] media Media device pointer
>> + * \return A unique pointer to a newly constructed instance of the Converter
>> + * subclass corresponding to the factory
>> + */
>> +
>> +/**
>> + * \def REGISTER_CONVERTER
>> + * \brief Register a converter with the Converter factory
>> + * \param[in] name Converter name used to register the class
>> + * \param[in] converter Class name of Converter derived class to register
>> + * \param[in] aliases Optional list of alias names
>> + *
>> + * Register a Converter subclass with the factory and make it available to try
>> + * and match converters.
>> + */
>> +
>> +} /* namespace libcamera */
>> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
>> index 7fcbb2dd..3a9fc31f 100644
>> --- a/src/libcamera/meson.build
>> +++ b/src/libcamera/meson.build
>> @@ -13,6 +13,7 @@ libcamera_sources = files([
>>       'controls.cpp',
>>       'control_serializer.cpp',
>>       'control_validator.cpp',
>> +    'converter.cpp',
>>       'delayed_controls.cpp',
>>       'device_enumerator.cpp',
>>       'device_enumerator_sysfs.cpp',
>> --
>> 2.37.3
>>
Regards,
   Xavier