Re: [PATCH v2 1/7] media: Add 2-10-10-10 RGB formats

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Tomi,

On Tue, Dec 20, 2022 at 04:12:29PM +0200, Tomi Valkeinen wrote:
> On 19/12/2022 21:10, Laurent Pinchart wrote:
> > On Mon, Dec 19, 2022 at 04:01:33PM +0200, Tomi Valkeinen wrote:
> >> Add XBGR2101010, ABGR2101010 and BGRA1010102 formats.
> >>
> >> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
> >> ---
> >>   .../userspace-api/media/v4l/pixfmt-rgb.rst    | 194 ++++++++++++++++++
> >>   drivers/media/v4l2-core/v4l2-ioctl.c          |   3 +
> >>   include/uapi/linux/videodev2.h                |   3 +
> >>   3 files changed, 200 insertions(+)
> >>
> >> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-rgb.rst b/Documentation/userspace-api/media/v4l/pixfmt-rgb.rst
> >> index 30f51cd33f99..de78cd2dcd73 100644
> >> --- a/Documentation/userspace-api/media/v4l/pixfmt-rgb.rst
> >> +++ b/Documentation/userspace-api/media/v4l/pixfmt-rgb.rst
> >> @@ -763,6 +763,200 @@ nomenclature that instead use the order of components as seen in a 24- or
> >>       \normalsize
> >>   
> >>   
> >> +10 Bits Per Component
> >> +=====================
> >> +
> >> +These formats store a 30-bit RGB triplet with an optional 2 bit alpha in four
> >> +bytes. They are named based on the order of the RGB components as seen in a
> >> +32-bit word, which is then stored in memory in little endian byte order
> >> +(unless otherwise noted by the presence of bit 31 in the 4CC value), and on the
> >> +number of bits for each component.
> >> +
> >> +.. raw:: latex
> >> +
> >> +    \begingroup
> >> +    \tiny
> >> +    \setlength{\tabcolsep}{2pt}
> >> +
> >> +.. tabularcolumns:: |p{2.8cm}|p{2.0cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|p{0.22cm}|
> >> +
> >> +
> >> +.. flat-table:: RGB Formats 10 Bits Per Color Component
> >> +    :header-rows:  2
> >> +    :stub-columns: 0
> >> +
> >> +    * - Identifier
> >> +      - Code
> >> +      - :cspan:`7` Byte 0 in memory
> >> +      - :cspan:`7` Byte 1
> >> +      - :cspan:`7` Byte 2
> >> +      - :cspan:`7` Byte 3
> >> +    * -
> >> +      -
> >> +      - 7
> >> +      - 6
> >> +      - 5
> >> +      - 4
> >> +      - 3
> >> +      - 2
> >> +      - 1
> >> +      - 0
> >> +
> >> +      - 7
> >> +      - 6
> >> +      - 5
> >> +      - 4
> >> +      - 3
> >> +      - 2
> >> +      - 1
> >> +      - 0
> >> +
> >> +      - 7
> >> +      - 6
> >> +      - 5
> >> +      - 4
> >> +      - 3
> >> +      - 2
> >> +      - 1
> >> +      - 0
> >> +
> >> +      - 7
> >> +      - 6
> >> +      - 5
> >> +      - 4
> >> +      - 3
> >> +      - 2
> >> +      - 1
> >> +      - 0
> >> +    * .. _V4L2-PIX-FMT-XBGR2101010:
> >> +
> >> +      - ``V4L2_PIX_FMT_XBGR2101010``
> >> +      - 'RX30'
> >> +
> >> +      - b\ :sub:`5`
> >> +      - b\ :sub:`4`
> >> +      - b\ :sub:`3`
> >> +      - b\ :sub:`2`
> >> +      - b\ :sub:`1`
> >> +      - b\ :sub:`0`
> >> +      - x
> >> +      - x
> >> +
> >> +      - g\ :sub:`3`
> >> +      - g\ :sub:`2`
> >> +      - g\ :sub:`1`
> >> +      - g\ :sub:`0`
> >> +      - b\ :sub:`9`
> >> +      - b\ :sub:`8`
> >> +      - b\ :sub:`7`
> >> +      - b\ :sub:`6`
> >> +
> >> +      - r\ :sub:`1`
> >> +      - r\ :sub:`0`
> >> +      - g\ :sub:`9`
> >> +      - g\ :sub:`8`
> >> +      - g\ :sub:`7`
> >> +      - g\ :sub:`6`
> >> +      - g\ :sub:`5`
> >> +      - g\ :sub:`4`
> >> +
> >> +      - r\ :sub:`9`
> >> +      - r\ :sub:`8`
> >> +      - r\ :sub:`7`
> >> +      - r\ :sub:`6`
> >> +      - r\ :sub:`5`
> >> +      - r\ :sub:`4`
> >> +      - r\ :sub:`3`
> >> +      - r\ :sub:`2`
> >> +      -
> > 
> > This doesn't match the text above. This would be RGBX2101010. I'm not
> > sure which format you want, so I don't know if it's the documentation or
> > the format name that is incorrect. The next two formats also seem
> > incorrect to me.
> 
> Right, the text should say big endian instead of little endian.

No, in big-endian format, you would have, for instance,
V4L2_PIX_FMT_XBGR2101010 defined as

	[x, x, B[9:4]], [B[3:0], G[9:6]], [G[5:0], R[1:0]], [R[7:0]]

in memory byte order, while the format you want to define is

	[B[5:0], x, x], [G[3:0], B[9:6]], [R[1:0], G[9:4]], [R[9:2]]

The issue here is that 10-bpp formats don't have an integer number of
bytes per component. They are thus more similar to the 16-bit RGB
formats, where the macro named defined the order in a 16-bit word, which
was then stored in little-endian format in memory. For 24-bit and 32-bit
formats, we departed from that rule by using the byte memory order in
the macro name. For 10-bpp RGB formats we can't do so anymore. The most
sensible option is thus, I think, to use the same naming scheme as the
16-bit RGB formats, which incidentaly matches the DRM naming scheme.

-- 
Regards,

Laurent Pinchart