[PATCH 3/9] libcamera: v4l2_subdevice: Expose media bus format info as internal API

[Jacopo Mondi]

Hi Laurent

On Tue, Feb 27, 2024 at 04:09:47PM +0200, Laurent Pinchart wrote:
> The V4L2SubdeviceFormatInfo structure, internal to the
> v4l2_subdevice.cpp compilation unit, contains information about media
> bus formats that will be useful in other parts of libcamera. To prepare
> for this, expose the structure in the v4l2_subdevice.h header and turn
> it into a class with a similar design as PixelFormatInfo.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  include/libcamera/internal/v4l2_subdevice.h | 13 +++
>  src/libcamera/v4l2_subdevice.cpp            | 94 ++++++++++++++-------
>  2 files changed, 76 insertions(+), 31 deletions(-)
>
> diff --git a/include/libcamera/internal/v4l2_subdevice.h b/include/libcamera/internal/v4l2_subdevice.h
> index 17db311bcfb3..a4df9ddfd322 100644
> --- a/include/libcamera/internal/v4l2_subdevice.h
> +++ b/include/libcamera/internal/v4l2_subdevice.h
> @@ -29,6 +29,19 @@ namespace libcamera {
>
>  class MediaDevice;
>
> +class MediaBusFormatInfo
> +{
> +public:
> +	bool isValid() const { return code != 0; }
> +
> +	static const MediaBusFormatInfo &info(uint32_t code);
> +
> +	const char *name;
> +	uint32_t code;
> +	unsigned int bitsPerPixel;
> +	PixelFormatInfo::ColourEncoding colourEncoding;
> +};
> +
>  struct V4L2SubdeviceCapability final : v4l2_subdev_capability {
>  	bool isReadOnly() const
>  	{
> diff --git a/src/libcamera/v4l2_subdevice.cpp b/src/libcamera/v4l2_subdevice.cpp
> index a74b8362b6d1..fd289ae9ae6f 100644
> --- a/src/libcamera/v4l2_subdevice.cpp
> +++ b/src/libcamera/v4l2_subdevice.cpp
> @@ -36,28 +36,40 @@ namespace libcamera {
>
>  LOG_DECLARE_CATEGORY(V4L2)
>
> +/**
> + * \class MediaBusFormatInfo
> + * \brief Information about media bus formats
> + *
> + * The MediaBusFormatInfo class groups together information describing a media
> + * bus format. It facilitates handling of media bus formats by providing data
> + * commonly used in pipeline handlers.
> + *
> + * \var MediaBusFormatInfo::name
> + * \brief The format name as a human-readable string, used as the text
> + * representation of the format
> + *
> + * \var MediaBusFormatInfo::code
> + * \brief The media bus format code described by this instance

Is it worth saying it's one of the MEDIA_BUS_FMT_ entries defined by
V4L2 ?

> + *
> + * \var MediaBusFormatInfo::bitsPerPixel
> + * \brief The average number of bits per pixel
> + *
> + * The number of bits per pixel averages the total number of bits for all
> + * colour components over the whole image, excluding any padding bits or
> + * padding pixels.

Not sure I got why it's an average here

> + *
> + * For formats that transmit multiple or fractional pixels per sample, the
> + * value will differ from the bus width.

Is this relevant ? Isn't this related to the HW bus width ?

> + *
> + * Formats that don't have a fixed number of bits per pixel, such as compressed
> + * formats, report 0 in this field.
> + *
> + * \var MediaBusFormatInfo::colourEncoding
> + * \brief The colour encoding type
> + */
> +
>  namespace {
>
> -/*
> - * \struct MediaBusFormatInfo
> - * \brief Information about media bus formats
> - * \param name Name of MBUS format
> - * \param code The media bus format code
> - * \param bitsPerPixel Bits per pixel
> - * \param colourEncoding Type of colour encoding
> - */
> -struct MediaBusFormatInfo {
> -	const char *name;
> -	uint32_t code;
> -	unsigned int bitsPerPixel;
> -	PixelFormatInfo::ColourEncoding colourEncoding;
> -};
> -
> -/*
> - * \var mediaBusFormatInfo
> - * \brief A map that associates MediaBusFormatInfo struct to V4L2 media
> - * bus codes
> - */
>  const std::map<uint32_t, MediaBusFormatInfo> mediaBusFormatInfo{
>  	/* This table is sorted to match the order in linux/media-bus-format.h */
>  	{ MEDIA_BUS_FMT_RGB444_2X8_PADHI_BE, {
> @@ -533,6 +545,33 @@ const std::map<uint32_t, MediaBusFormatInfo> mediaBusFormatInfo{
>
>  } /* namespace */
>
> +/**
> + * \fn bool MediaBusFormatInfo::isValid() const
> + * \brief Check if the media bus format info is valid
> + * \return True if the media bus format info is valid, false otherwise
> + */
> +
> +/**
> + * \brief Retrieve information about a media bus format
> + * \param[in] code The media bus format code
> + * \return The MediaBusFormatInfo describing the \a code if known, or an invalid
> + * MediaBusFormatInfo otherwise
> + */
> +const MediaBusFormatInfo &MediaBusFormatInfo::info(uint32_t code)
> +{
> +	static const MediaBusFormatInfo invalid{};
> +
> +	const auto it = mediaBusFormatInfo.find(code);
> +	if (it == mediaBusFormatInfo.end()) {
> +		LOG(V4L2, Warning)
> +			<< "Unsupported media bus format "

Fitst on the previous line

> +			<< utils::hex(code, 4);
> +		return invalid;
> +	}
> +
> +	return it->second;
> +}
> +
>  /**
>   * \struct V4L2SubdeviceCapability
>   * \brief struct v4l2_subdev_capability object wrapper and helpers
> @@ -629,14 +668,7 @@ const std::string V4L2SubdeviceFormat::toString() const
>   */
>  uint8_t V4L2SubdeviceFormat::bitsPerPixel() const
>  {
> -	const auto it = mediaBusFormatInfo.find(mbus_code);
> -	if (it == mediaBusFormatInfo.end()) {
> -		LOG(V4L2, Error) << "No information available for format '"
> -				 << *this << "'";
> -		return 0;
> -	}
> -
> -	return it->second.bitsPerPixel;
> +	return MediaBusFormatInfo::info(mbus_code).bitsPerPixel;
>  }
>
>  /**
> @@ -903,9 +935,9 @@ std::optional<ColorSpace> V4L2Subdevice::toColorSpace(const v4l2_mbus_framefmt &
>  		return std::nullopt;
>
>  	PixelFormatInfo::ColourEncoding colourEncoding;
> -	auto iter = mediaBusFormatInfo.find(format.code);
> -	if (iter != mediaBusFormatInfo.end()) {
> -		colourEncoding = iter->second.colourEncoding;
> +	const MediaBusFormatInfo &info = MediaBusFormatInfo::info(format.code);
> +	if (info.isValid()) {
> +		colourEncoding = info.colourEncoding;
>  	} else {
>  		LOG(V4L2, Warning)
>  			<< "Unknown subdev format "
> --
> Regards,
>
> Laurent Pinchart
>