linux-kernel - Re: [PATCH] v4l: Add source change event for colorimetry

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Message-ID: <CAAFQd5AYvMrZQtZ2UBOEG6Nar06bZrRZdE57Y6N7+6dZxJ0m_A@mail.gmail.com>
Date:   Tue, 13 Oct 2020 15:40:56 +0200
From:   Tomasz Figa <tfiga@...omium.org>
To:     Stanimir Varbanov <stanimir.varbanov@...aro.org>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nicolas Dufresne <nicolas@...fresne.ca>
Subject: Re: [PATCH] v4l: Add source change event for colorimetry

On Tue, Oct 13, 2020 at 11:03 AM Stanimir Varbanov
<stanimir.varbanov@...aro.org> wrote:
>
> Hi,
>
> On 7/2/20 2:52 PM, Stanimir Varbanov wrote:
> > Hi,
> >
> > Once we have this event there is still open question how the client will
> > know the data buffer on which the new colorspace is valid/applied.
> >
> > The options could be:
> >  * a new buffer flag and
> >  * some information in the v4l2_event structure.
> >
> > Thoughts?
>
> Kindly ping.
>

The event itself sounds good to me, but how do we know which buffer is
the first to have the new colorimetry?

Best regards,
Tomasz

> >
> > On 7/2/20 1:00 PM, Stanimir Varbanov wrote:
> >> This event indicate that the source colorspace is changed
> >> during run-time. The client has to retrieve the new colorspace
> >> identifiers by getting the format (G_FMT).
> >>
> >> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
> >> ---
> >>  .../userspace-api/media/v4l/vidioc-dqevent.rst        | 11 ++++++++++-
> >>  .../userspace-api/media/videodev2.h.rst.exceptions    |  1 +
> >>  include/uapi/linux/videodev2.h                        |  1 +
> >>  3 files changed, 12 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst b/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst
> >> index a9a176d5256d..3f69c753db58 100644
> >> --- a/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst
> >> +++ b/Documentation/userspace-api/media/v4l/vidioc-dqevent.rst
> >> @@ -381,7 +381,16 @@ call.
> >>      that many Video Capture devices are not able to recover from a temporary
> >>      loss of signal and so restarting streaming I/O is required in order for
> >>      the hardware to synchronize to the video signal.
> >> -
> >> +    * - ``V4L2_EVENT_SRC_CH_COLORIMETRY``
> >> +      - 0x0002
> >> +      - This event gets triggered when a colorspace change is detected at
> >> +    an input. By colorspace change here we include also changes in the
> >> +    colorspace specifiers (transfer function, Y'CbCr encoding and
> >> +    quantization). This event can come from an input or from video decoder.
> >> +    Once the event has been send to the client the driver has to update
> >> +    the colorspace specifiers internally so that they could be retrieved by
> >> +    client. In that case queue re-negotiation is not needed as this change
> >> +    only reflects on the interpretation of the data.
> >>
> >>  Return Value
> >>  ============
> >> diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> >> index ca05e4e126b2..54fc21af852d 100644
> >> --- a/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> >> +++ b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
> >> @@ -492,6 +492,7 @@ replace define V4L2_EVENT_CTRL_CH_FLAGS ctrl-changes-flags
> >>  replace define V4L2_EVENT_CTRL_CH_RANGE ctrl-changes-flags
> >>
> >>  replace define V4L2_EVENT_SRC_CH_RESOLUTION src-changes-flags
> >> +replace define V4L2_EVENT_SRC_CH_COLORIMETRY src-changes-flags
> >>
> >>  replace define V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ :c:type:`v4l2_event_motion_det`
> >>
> >> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> >> index 303805438814..b5838bc4e3a3 100644
> >> --- a/include/uapi/linux/videodev2.h
> >> +++ b/include/uapi/linux/videodev2.h
> >> @@ -2351,6 +2351,7 @@ struct v4l2_event_frame_sync {
> >>  };
> >>
> >>  #define V4L2_EVENT_SRC_CH_RESOLUTION                (1 << 0)
> >> +#define V4L2_EVENT_SRC_CH_COLORIMETRY               (1 << 1)
> >>
> >>  struct v4l2_event_src_change {
> >>      __u32 changes;
> >>
> >
>
> --
> regards,
> Stan