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

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Date:   Mon, 13 Feb 2023 11:38:40 -0500
From:   Nicolas Dufresne <nicolas@...fresne.ca>
To:     Ming Qian <ming.qian@....com>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "Mirela Rabulea (OSS)" <mirela.rabulea@....nxp.com>,
        "hverkuil-cisco@...all.nl" <hverkuil-cisco@...all.nl>
Cc:     "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "X.H. Bao" <xiahong.bao@....com>, dl-linux-imx <linux-imx@....com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [EXT] Re: [PATCH v2 02/10] media: Add Y012 video format

Le lundi 13 février 2023 à 09:22 +0000, Ming Qian a écrit :
> > From: Nicolas Dufresne <nicolas@...fresne.ca>
> > Sent: 2023年2月10日 23:18
> > To: Ming Qian <ming.qian@....com>; mchehab@...nel.org; Mirela Rabulea
> > (OSS) <mirela.rabulea@....nxp.com>; hverkuil-cisco@...all.nl
> > Cc: shawnguo@...nel.org; s.hauer@...gutronix.de; kernel@...gutronix.de;
> > festevam@...il.com; X.H. Bao <xiahong.bao@....com>; dl-linux-imx <linux-
> > imx@....com>; linux-media@...r.kernel.org; linux-kernel@...r.kernel.org;
> > devicetree@...r.kernel.org; linux-arm-kernel@...ts.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@....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  */
>