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

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Date:   Thu, 9 Jan 2020 09:41:00 +0200
From:   Stanimir Varbanov <stanimir.varbanov@...aro.org>
To:     Hans Verkuil <hverkuil@...all.nl>, 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

Hi Hans,

On 1/8/20 6:09 PM, Hans Verkuil wrote:
> 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

What you mean by "but not a resolution change" here? Resolution change
and bit-depth change cannot occur on the same time, or something else.

I would say that for Venus (and probably others) on initialization time
both could be changed on the same time, because we cannot predict the
resolution and bit-depth before parsing bitstream headers.

> 	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;
>>
> 

-- 
regards,
Stan