Re: [PATCH v2 1/2] v4l: Add resolution change event.

[Hans Verkuil <hverkuil@xs4all.nl>]

On 05/05/2014 11:50 AM, Arun Kumar K wrote:
> Hi Hans,
> 
> On Wed, Apr 30, 2014 at 8:03 PM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>> On 04/30/2014 12:38 PM, Arun Kumar K wrote:
>>> Hi Hans,
>>>
>>>
>>> On 04/22/14 18:22, Hans Verkuil wrote:
>>>> On 04/21/2014 11:26 AM, Arun Kumar K wrote:
>>>>> From: Pawel Osciak <posciak@chromium.org>
>>>>>
>>>>> This event indicates that the decoder has reached a point in the stream,
>>>>> at which the resolution changes. The userspace is expected to provide a new
>>>>> set of CAPTURE buffers for the new format before decoding can continue.
>>>>> The event can also be used for more generic events involving resolution
>>>>> or format changes at runtime for all kinds of video devices.
>>>>>
>>>>> Signed-off-by: Pawel Osciak <posciak@chromium.org>
>>>>> Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
>>>>> ---
>>>>>  .../DocBook/media/v4l/vidioc-subscribe-event.xml   |   16 ++++++++++++++++
>>>>>  include/uapi/linux/videodev2.h                     |    6 ++++++
>>>>>  2 files changed, 22 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
>>>>> index 5c70b61..0aec831 100644
>>>>> --- a/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
>>>>> +++ b/Documentation/DocBook/media/v4l/vidioc-subscribe-event.xml
>>>>> @@ -155,6 +155,22 @@
>>>>>         </entry>
>>>>>       </row>
>>>>>       <row>
>>>>> +       <entry><constant>V4L2_EVENT_SOURCE_CHANGE</constant></entry>
>>>>> +       <entry>5</entry>
>>>>> +       <entry>
>>>>> +         <para>This event is triggered when a resolution or format change
>>>>> +          is detected during runtime by the video device. It can be a
>>>>> +          runtime resolution change triggered by a video decoder or the
>>>>> +          format change happening on an HDMI connector. Application may
>>>>> +          need to reinitialize buffers before proceeding further.</para>
>>>>> +
>>>>> +              <para>This event has a &v4l2-event-source-change; associated
>>>>> +         with it. This has significance only for v4l2 subdevs where the
>>>>> +         <structfield>pad_num</structfield> field will be updated with
>>>>> +         the pad number on which the event is triggered.</para>
>>>>> +       </entry>
>>>>> +     </row>
>>>>> +     <row>
>>>>>         <entry><constant>V4L2_EVENT_PRIVATE_START</constant></entry>
>>>>>         <entry>0x08000000</entry>
>>>>>         <entry>Base event number for driver-private events.</entry>
>>>>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>>>>> index 6ae7bbe..12e0614 100644
>>>>> --- a/include/uapi/linux/videodev2.h
>>>>> +++ b/include/uapi/linux/videodev2.h
>>>>> @@ -1733,6 +1733,7 @@ struct v4l2_streamparm {
>>>>>  #define V4L2_EVENT_EOS                             2
>>>>>  #define V4L2_EVENT_CTRL                            3
>>>>>  #define V4L2_EVENT_FRAME_SYNC                      4
>>>>> +#define V4L2_EVENT_SOURCE_CHANGE           5
>>>>>  #define V4L2_EVENT_PRIVATE_START           0x08000000
>>>>>
>>>>>  /* Payload for V4L2_EVENT_VSYNC */
>>>>> @@ -1764,12 +1765,17 @@ struct v4l2_event_frame_sync {
>>>>>     __u32 frame_sequence;
>>>>>  };
>>>>>
>>>>> +struct v4l2_event_source_change {
>>>>> +   __u32 pad_num;
>>>>> +};
>>>>> +
>>>>>  struct v4l2_event {
>>>>>     __u32                           type;
>>>>>     union {
>>>>>             struct v4l2_event_vsync         vsync;
>>>>>             struct v4l2_event_ctrl          ctrl;
>>>>>             struct v4l2_event_frame_sync    frame_sync;
>>>>> +           struct v4l2_event_source_change source_change;
>>>>>             __u8                            data[64];
>>>>>     } u;
>>>>>     __u32                           pending;
>>>>>
>>>>
>>>> This needs to be done differently. The problem is that you really have multiple
>>>> events that you want to subscribe to: one for each pad (or input: see the way
>>>> VIDIOC_G/S_EDID maps pad to an input or output index when used with a video node,
>>>> we have to support that for this event as well).
>>>>
>>>> What you want to do is similar to what is done for control events: there you can
>>>> subscribe for a specific control and get notified when that control changes.
>>>>
>>>> The way that works in the event code is that the 'id' field in the v4l2_event
>>>> struct contains that control ID, or, in this case, the pad/input/output index.
>>>>
>>>
>>> As I am new to v4l2-events itself, I might have some noob questions.
>>> I understood filling pad index into id field. But for video nodes,
>>> the application is supposed to put v4l2_buf_type in the id field?
>>
>> No, a capture video node can have multiple inputs (those are enumerated with
>> VIDIOC_ENUMINPUTS), and each input can generate a SOURCE_CHANGE event, even if it
>> is not the currently active input. Hence the need of setting id to the input
>> index. v4l2_buf_type makes no sense here.
>>
> 
> Ok. But in a simple m2m device like mfc, the userspace has to subscribe to
> the event say on the CAPTURE plane where buffers has to be re-allocated on
> resolution change. So in such a case, what should be put in id field?

M2M devices will only have one input and one output, so the ID will be 0.

Regards,

	Hans