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Subject: Re: [PATCH] v4l: Add source change event for colorimetry
To:     Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Tomasz Figa <tfiga@chromium.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Nicolas Dufresne <nicolas@ndufresne.ca>
References: <20200702100017.24700-1-stanimir.varbanov@linaro.org>
From:   Stanimir Varbanov <stanimir.varbanov@linaro.org>
Message-ID: <8dafbb4b-4626-5191-c57a-f3ef19c14618@linaro.org>
Date:   Thu, 2 Jul 2020 14:52:38 +0300
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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?

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@linaro.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