[PATCH v2 03/14] libcamera: v4l2_subdevice: Expose media bus format info as internal API

[Kieran Bingham]

Quoting Laurent Pinchart (2024-03-15 00:16:02)
> 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>
> Reviewed-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
> ---
> Changes since v1:
> 
> - Improve MediaBusFormatInfo::code documentation

LGTM


Reviewed-by: Kieran Bingham <kieran.bingham 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 1286e7c385c4..4918e28e5f18 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 (MEDIA_BUS_FMT_*)
> + *
> + * \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.
> + *
> + * For formats that transmit multiple or fractional pixels per sample, the
> + * value will differ from the 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, {
> @@ -557,6 +569,33 @@ 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 "
> +                       << utils::hex(code, 4);
> +               return invalid;
> +       }
> +
> +       return it->second;
> +}
> +
>  /**
>   * \struct V4L2SubdeviceCapability
>   * \brief struct v4l2_subdev_capability object wrapper and helpers
> @@ -653,14 +692,7 @@ 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;
>  }
>  
>  /**
> @@ -927,9 +959,9 @@ 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
>