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SubjectRe: [PATCH v4 04/12] v4l: Add source event change for bit-depth
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On 1/9/20 8:41 AM, Stanimir Varbanov wrote:
> 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@linux.intel.com>
>>> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.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.

What I was trying to say is that a resolution change implies a possible bit-depth
change as well, whereas V4L2_EVENT_SRC_CH_COLOR_DEPTH is only set if there is
a bit-depth change but no resolution change.

V4L2_EVENT_SRC_CH_RESOLUTION requires that userspace does a full resync to the
new format, CH_COLOR_DEPTH implies that only the bit depth changed.

Which actually makes me wonder: is there a difference between the two change flags
w.r.t. userspace behavior? If there is, then that should be carefully documented,
if there isn't, then is this new flag really needed?

Regards,

Hans

>
> 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;
>>>
>>
>

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