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

[Arun Kumar K <arunkk.samsung@gmail.com>]

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?


> In the application you will subscribe to the SOURCE_CHANGE event for a specific
> pad/input/output index.
> 
> In other words, the pad_num field should be dropped and the id field used
> instead.
> 
> Assuming we will also add a 'changes' field (see my reply to the other post
> on that topic), then you should also provide replace and merge ops (see
> v4l2-ctrls.c). That way it is sufficient to use just one element when calling
> v4l2_event_subscribe(): you will never loose information since if multiple
> events arrive before the application can dequeue them, the 'changes' information
> will be the ORed value of all those intermediate events.
> 

If I understand correctly, the implementation should go somewhat in the
following lines:

+void v4l2_event_src_replace(struct v4l2_event *old, const struct
v4l2_event *new)
+{
+       u32 old_changes = old->u.src_change.changes;
+
+       old->u.src_change = new->u.src_change;
+       old->u.src_change.changes |= old_changes;
+}
+
+void v4l2_event_src_merge(const struct v4l2_event *old, struct
v4l2_event *new)
+{
+       new->u.src_change.changes |= old->u.src_change.changes;
+}
+
+const struct v4l2_subscribed_event_ops v4l2_event_src_ch_ops = {
+       .replace = v4l2_event_src_replace,
+       .merge = v4l2_event_src_merge,
+};
+
+int v4l2_src_change_event_subscribe(struct v4l2_fh *fh,
+                               const struct v4l2_event_subscription *sub)
+{
+       if (sub->type == V4L2_EVENT_SOURCE_CHANGE)
+               return v4l2_event_subscribe(fh, sub, 0,
&v4l2_event_src_ch_ops);
+       return -EINVAL;
+}

And v4l2-event.c is the right place to put it?


And in the videodev2.h file:

+#define V4L2_EVENT_SRC_CH_RESOLUTION           (1 << 0)
+#define V4L2_EVENT_SRC_CH_FORMAT               (1 << 1)
+
+struct v4l2_event_src_change {
+       __u32 changes;
+};
+
 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_src_change    src_change;
                __u8                            data[64];
        } u;
        __u32                           pending;

Please correct me if my understanding is totally wrong here?

Regards
Arun

> It's all more work, but it is critical to ensure that the application never
> misses events.
> 
> Regards,
> 
> 	Hans
>