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

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Message-ID: <CAAFQd5DP0qMExsBY4UEhP9gLNUfwokzn3S7sgkAZPMTkkt7M6w@mail.gmail.com>
Date:   Tue, 13 Oct 2020 16:56:54 +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 4:53 PM Stanimir Varbanov
<stanimir.varbanov@...aro.org> wrote:
>
>
>
> On 10/13/20 5:07 PM, Tomasz Figa wrote:
> > On Tue, Oct 13, 2020 at 3:53 PM Stanimir Varbanov
> > <stanimir.varbanov@...aro.org> wrote:
> >>
> >>
> >>
> >> On 10/13/20 4:40 PM, Tomasz Figa wrote:
> >>> 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?
> >>
> >> I think Hans have a very good idea to have width/height and colorspace
> >> specifiers in v4l2_ext_buffer [1].
> >>
> >> [1] https://lkml.org/lkml/2020/9/9/531
> >>
> >
> > Hmm, I think that would basically make the event obsolete and without
> > solving that problem I suspect the event is not very useful, because
> > one could already receive and display (incorrectly) some buffers
> > before realizing that they have different colorimetry
>
> Yes, I agree. I wasn't sure does Hans's idea will be well received, thus
> I pinged.
>
> >
> > I believe for now we would have to handle this like a resolution
> > change - flush the CAPTURE queue and the next buffer after the flush
> > would have the new colorimetry. With the new API we could optimize the
>
> I'm not sure what you mean by flush capture queue? Dequeue until LAST
> flag (EPIPE) and stop streaming g_fmt(capture queue) and decide what is
> changed and start streaming ?

Yes, although no strict need to stop streaming, other ways are defined
as well, e.g. DEC_CMD_START.

Of course we would need to make appropriate changes to the spec and so
I'd just unify it with the resolution change sequence. I think we
could rename it to "Stream parameter change".

>
> > decoding by getting rid of the flushes and relying on the in-bound
> > information.
> >
> > Best regards,
> > Tomasz
> >
> >>>
> >>> 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
> >>
> >> --
> >> regards,
> >> Stan
>
> --
> regards,
> Stan