linux-kernel - Re: [PATCH v4 04/12] v4l: Add source event change for bit-depth

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Date:   Wed, 8 Jan 2020 17:09:31 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org
Cc:     Vikash Garodia <vgarodia@...eaurora.org>, dikshita@...eaurora.org
Subject: Re: [PATCH v4 04/12] v4l: Add source event change for bit-depth

On 1/6/20 4:49 PM, Stanimir Varbanov wrote:
> This event indicate that the source color bit-depth is changed
> during run-time. The client must get the new format and re-allocate
> buffers for it. This can usually happens with video decoder (encoders)
> when the bit-stream color bit-depth is changed from 8 to 10bits
> or vice versa.
> 
> Acked-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@...aro.org>
> ---
>  Documentation/media/uapi/v4l/vidioc-dqevent.rst | 8 +++++++-
>  Documentation/media/videodev2.h.rst.exceptions  | 1 +
>  include/uapi/linux/videodev2.h                  | 1 +
>  3 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/media/uapi/v4l/vidioc-dqevent.rst b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> index 42659a3d1705..fad853d440cf 100644
> --- a/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> @@ -402,7 +402,13 @@ 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_COLOR_DEPTH``
> +      - 0x0002
> +      - This event gets triggered when color bit-depth change is detected
> +	from a video decoder. Applications will have to query the new pixel
> +	format and re-negotiate the queue. In most cases the streaming must be
> +	stopped and restarted (:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
> +	followed by :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`).

I think this is too specific for decoders. Something similar to the
CH_RESOLUTION description would be more appropriate:

      - This event gets triggered when a color bit-depth change (but not a
	resolution change!) is detected	at an input. This can come from an
	input connector or from a video decoder. Applications will have to query
	the new pixel format and re-negotiate the queue.

	For stateful decoders follow the guidelines in :ref:`decoder`.
	Video capture devices will in most cases have to stop and restart
	streaming (:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` followed by
	:ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`).

And update dev-decoder.rst where needed with this new event flag.

As to your question on irc: once I've acked this patch it can be merged
via a venus PR.

Regards,

	Hans

>  
>  Return Value
>  ============
> diff --git a/Documentation/media/videodev2.h.rst.exceptions b/Documentation/media/videodev2.h.rst.exceptions
> index cb6ccf91776e..209709114378 100644
> --- a/Documentation/media/videodev2.h.rst.exceptions
> +++ b/Documentation/media/videodev2.h.rst.exceptions
> @@ -490,6 +490,7 @@ 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_COLOR_DEPTH 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 5f9357dcb060..1d349c9d57a7 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -2332,6 +2332,7 @@ struct v4l2_event_frame_sync {
>  };
>  
>  #define V4L2_EVENT_SRC_CH_RESOLUTION		(1 << 0)
> +#define V4L2_EVENT_SRC_CH_COLOR_DEPTH		(1 << 1)
>  
>  struct v4l2_event_src_change {
>  	__u32 changes;
>