media: v4l2: add support for colorspace conversion API (CSC) for video capture

For video capture it is the driver that reports the colorspace, transfer function, Y'CbCr/HSV encoding and quantization range used by the video, and there is no way to request something different, even though many HDTV receivers have some sort of colorspace conversion capabilities. For output video this feature already exists since the application specifies this information for the video format it will send out, and the transmitter will enable any available CSC if a format conversion has to be performed in order to match the capabilities of the sink. For video capture we propose adding new v4l2_pix_format flag: V4L2_PIX_FMT_FLAG_SET_CSC. The flag is set by the application, the driver will interpret the colorspace, xfer_func, ycbcr_enc/hsv_enc and quantization fields as the requested colorspace information and will attempt to do the conversion it supports. Drivers set the flags V4L2_FMT_FLAG_CSC_COLORSPACE, V4L2_FMT_FLAG_CSC_XFER_FUNC, V4L2_FMT_FLAG_CSC_YCBCR_ENC/V4L2_FMT_FLAG_CSC_HSV_ENC, V4L2_FMT_FLAG_CSC_QUANTIZATION, in the flags field of the struct v4l2_fmtdesc during enumeration to indicate that they support colorspace conversion for the respective field. Drivers do not have to actually look at the flags. If the flags are not set, then the fields 'colorspace', 'xfer_func', 'ycbcr_enc/hsv_enc', and 'quantization' are set to the default values by the core, i.e. just pass on the received format without conversion.

DHDafna Hirschfeld committed 6 years ago