[EXT] Re: [PATCH v2 02/10] media: Add Y012 video format

[Nicolas Dufresne]

Le lundi 13 février 2023 à 09:22 +0000, Ming Qian a écrit :
> > From: Nicolas Dufresne <nicolas at ndufresne.ca>
> > Sent: 2023年2月10日 23:18
> > To: Ming Qian <ming.qian at nxp.com>; mchehab at kernel.org; Mirela Rabulea
> > (OSS) <mirela.rabulea at oss.nxp.com>; hverkuil-cisco at xs4all.nl
> > Cc: shawnguo at kernel.org; s.hauer at pengutronix.de; kernel at pengutronix.de;
> > festevam at gmail.com; X.H. Bao <xiahong.bao at nxp.com>; dl-linux-imx <linux-
> > imx at nxp.com>; linux-media at vger.kernel.org; linux-kernel at vger.kernel.org;
> > devicetree at vger.kernel.org; linux-arm-kernel at lists.infradead.org
> > Subject: [EXT] Re: [PATCH v2 02/10] media: Add Y012 video format
> > 
> > Caution: EXT Email
> > 
> > Le mercredi 01 février 2023 à 14:02 +0800, Ming Qian a écrit :
> > > Y012 is a luma-only formats with 12-bits per pixel, expanded to
> > > 16bits.
> > > Data in the 12 high bits, zeros in the 4 low bits, arranged in little
> > > endian order.
> > > 
> > > Signed-off-by: Ming Qian <ming.qian at nxp.com>
> > > ---
> > >  .../userspace-api/media/v4l/pixfmt-yuv-luma.rst       | 11 +++++++++++
> > >  drivers/media/v4l2-core/v4l2-ioctl.c                  |  1 +
> > >  include/uapi/linux/videodev2.h                        |  1 +
> > >  3 files changed, 13 insertions(+)
> > > 
> > > diff --git a/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst
> > > b/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst
> > > index 6a387f9df3ba..3ffa29000238 100644
> > > --- a/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst
> > > +++ b/Documentation/userspace-api/media/v4l/pixfmt-yuv-luma.rst
> > > @@ -103,6 +103,17 @@ are often referred to as greyscale formats.
> > >        - ...
> > >        - ...
> > > 
> > > +    * .. _V4L2-PIX-FMT-Y012:
> > 
> > Why the 0, can't this be name Y12 (just like Y14) ?
> > 
> 
> Hi Nicolas,
>     As the V4L2_PIX_FMT_Y12 is defined, but it's data is in the 12 low bits,
> zeros in the high bits.
>     Here I want to place the 12 bits data in the high bits, with zeros in the
> 4 low bits.
>     So I add 0 before 12, I want to say that the low bits are padding data 0.
>    
>     Or do you have a better suggestion?

I see, I had missed this aspect. I think in this context, it would be fair
naming. Maybe drop a note in the doc saying just that:

"In contrast to V4L2_PIX_FMT_Y12 format, which have its padding located in the
most significant bits of the 16 bit word".

Or something similar.,
Nicolas

> 
> Ming
> 
> > > +
> > > +      - ``V4L2_PIX_FMT_Y012``
> > > +      - 'Y012'
> > > +
> > > +      - Y'\ :sub:`0`\ [3:0] `0000`
> > > +      - Y'\ :sub:`0`\ [11:4]
> > > +      - ...
> > > +      - ...
> > > +      - ...
> > > +
> > >      * .. _V4L2-PIX-FMT-Y14:
> > > 
> > >        - ``V4L2_PIX_FMT_Y14``
> > > diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c
> > > b/drivers/media/v4l2-core/v4l2-ioctl.c
> > > index 067dbdd0a9ef..0ee730aa6cc7 100644
> > > --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> > > +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> > > @@ -1303,6 +1303,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc
> > *fmt)
> > >       case V4L2_PIX_FMT_Y6:           descr = "6-bit Greyscale"; break;
> > >       case V4L2_PIX_FMT_Y10:          descr = "10-bit Greyscale"; break;
> > >       case V4L2_PIX_FMT_Y12:          descr = "12-bit Greyscale"; break;
> > > +     case V4L2_PIX_FMT_Y012:         descr = "12-bit Greyscale"; break;
> > >       case V4L2_PIX_FMT_Y14:          descr = "14-bit Greyscale"; break;
> > >       case V4L2_PIX_FMT_Y16:          descr = "16-bit Greyscale"; break;
> > >       case V4L2_PIX_FMT_Y16_BE:       descr = "16-bit Greyscale BE";
> > > break;
> > > diff --git a/include/uapi/linux/videodev2.h
> > > b/include/uapi/linux/videodev2.h index 5448aa3b7858..3d8f89bff33c
> > > 100644
> > > --- a/include/uapi/linux/videodev2.h
> > > +++ b/include/uapi/linux/videodev2.h
> > > @@ -583,6 +583,7 @@ struct v4l2_pix_format {
> > >  #define V4L2_PIX_FMT_Y6      v4l2_fourcc('Y', '0', '6', ' ') /*  6 
> > > Greyscale     */
> > >  #define V4L2_PIX_FMT_Y10     v4l2_fourcc('Y', '1', '0', ' ') /* 10 
> > > Greyscale
> > */
> > >  #define V4L2_PIX_FMT_Y12     v4l2_fourcc('Y', '1', '2', ' ') /* 12 
> > > Greyscale
> > */
> > > +#define V4L2_PIX_FMT_Y012    v4l2_fourcc('Y', '0', '1', '2') /* 12 
> > > Greyscale
> > */
> > >  #define V4L2_PIX_FMT_Y14     v4l2_fourcc('Y', '1', '4', ' ') /* 14 
> > > Greyscale
> > */
> > >  #define V4L2_PIX_FMT_Y16     v4l2_fourcc('Y', '1', '6', ' ') /* 16 
> > > Greyscale
> > */
> > >  #define V4L2_PIX_FMT_Y16_BE  v4l2_fourcc_be('Y', '1', '6', ' ') /* 16
> > > Greyscale BE  */
>