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

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Date:   Tue, 13 Oct 2020 16:53:25 +0300
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Tomasz Figa <tfiga@...omium.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 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

> 
> 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