linux-kernel - RE: [EXT] Re: [PATCH] media: videobuf2: add V4L2_BUF_FLAG

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Date:   Tue, 5 Jul 2022 01:52:18 +0000
From:   Ming Qian <ming.qian@....com>
To:     Nicolas Dufresne <nicolas@...fresne.ca>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "hverkuil-cisco@...all.nl" <hverkuil-cisco@...all.nl>
CC:     "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.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>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [EXT] Re: [PATCH] media: videobuf2: add V4L2_BUF_FLAG_CODECCONFIG
 flag

> From: Nicolas Dufresne <nicolas@...fresne.ca>
> Sent: 2022年7月4日 23:53
> To: Ming Qian <ming.qian@....com>; mchehab@...nel.org;
> hverkuil-cisco@...all.nl
> Cc: shawnguo@...nel.org; robh+dt@...nel.org; s.hauer@...gutronix.de;
> kernel@...gutronix.de; festevam@...il.com; dl-linux-imx
> <linux-imx@....com>; linux-media@...r.kernel.org;
> linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org
> Subject: [EXT] Re: [PATCH] media: videobuf2: add
> V4L2_BUF_FLAG_CODECCONFIG flag
> 
> Caution: EXT Email
> 
> Le mardi 28 juin 2022 à 10:19 +0800, Ming Qian a écrit :
> > By setting the V4L2_BUF_FLAG_CODECCONFIG flag, user-space should be
> > able to hint decoder the vb2 only contains codec config header, but
> > does not contain any frame data.
> > It's only used for parsing header, and can't be decoded.
> 
> This is copied from OMX specification. I think we we import this, we should at
> least refer to the original.
> 

Hi Nicolas,
    Do you mean OMX_BUFFERFLAG_CODECCONFIG?
    I'm sorry that I didn't notice it before.
    Currently we only encounter this requirement on Android, I'm not sure if it has a reference to omx.
    And thank you very much for pointing out it.

Ming

> >
> > Current, it's usually used by android.
> >
> > Signed-off-by: Ming Qian <ming.qian@....com>
> > ---
> >  Documentation/userspace-api/media/v4l/buffer.rst | 9 +++++++++
> >  include/uapi/linux/videodev2.h                   | 2 ++
> >  2 files changed, 11 insertions(+)
> >
> > diff --git a/Documentation/userspace-api/media/v4l/buffer.rst
> > b/Documentation/userspace-api/media/v4l/buffer.rst
> > index 4638ec64db00..acdc4556f4f4 100644
> > --- a/Documentation/userspace-api/media/v4l/buffer.rst
> > +++ b/Documentation/userspace-api/media/v4l/buffer.rst
> > @@ -607,6 +607,15 @@ Buffer Flags
> >       the format. Any subsequent call to the
> >       :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore,
> >       but return an ``EPIPE`` error code.
> > +    * .. _`V4L2-BUF-FLAG-CODECCONFIG`:
> > +
> > +      - ``V4L2_BUF_FLAG_CODECCONFIG``
> > +      - 0x00200000
> > +      - This flag may be set when the buffer only contains codec config
> > +    header, but does not contain any frame data. Usually the codec config
> > +    header is merged to the next idr frame, with the flag
> > +    ``V4L2_BUF_FLAG_KEYFRAME``, but there is still some scenes that will
> > +    split the header and queue it separately.
> 
> I think the documentation is clear. Now, if a driver uses this, will existing
> userland (perhaps good to check GStreamer, FFMPEG and Chromium ?) will
> break ?
> So we need existing driver to do this when flagged to, and just copy/append
> when the userland didn't opt-in that feature ?
> 
> >      * .. _`V4L2-BUF-FLAG-REQUEST-FD`:
> >
> >        - ``V4L2_BUF_FLAG_REQUEST_FD``
> > diff --git a/include/uapi/linux/videodev2.h
> > b/include/uapi/linux/videodev2.h index 5311ac4fde35..8708ef257710
> > 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -1131,6 +1131,8 @@ static inline __u64 v4l2_timeval_to_ns(const
> struct timeval *tv)
> >  #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE         0x00010000
> >  /* mem2mem encoder/decoder */
> >  #define V4L2_BUF_FLAG_LAST                   0x00100000
> > +/* Buffer only contains codec header */
> > +#define V4L2_BUF_FLAG_CODECCONFIG            0x00200000
> >  /* request_fd is valid */
> >  #define V4L2_BUF_FLAG_REQUEST_FD             0x00800000
> >