Re: [PATCH v4 7/8] v4l: Add signal lock status to source change events

[Steve Longerbeam]

On 11/14/2016 03:36 AM, Hans Verkuil wrote:
> On 08/03/2016 08:03 PM, Steve Longerbeam wrote:
> > Add a signal lock status change to the source changes bitmask.
> > This indicates there was a signal lock or unlock event detected
> > at the input of a video decoder.
> >
> > Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
> > Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>
> >
> > ---
> >
> > v4:
> > - converted to rst from DocBook
> >
> > v3: no changes
> > v2: no changes
> > ---
> >   Documentation/media/uapi/v4l/vidioc-dqevent.rst | 9 +++++++++
> >   Documentation/media/videodev2.h.rst.exceptions  | 1 +
> >   include/uapi/linux/videodev2.h                  | 1 +
> >   3 files changed, 11 insertions(+)
> >
> > diff --git a/Documentation/media/uapi/v4l/vidioc-dqevent.rst b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> > index 73c0d5b..7d8a053 100644
> > --- a/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> > +++ b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
> > @@ -564,6 +564,15 @@ call.
> >   	  an input. This can come from an input connector or from a video
> >   	  decoder.
> >   
> > +    -  .. row 2
> > +
> > +       -  ``V4L2_EVENT_SRC_CH_LOCK_STATUS``
> > +
> > +       -  0x0002
> > +
> > +       -  This event gets triggered when there is a signal lock or
> > +	  unlock detected at the input of a video decoder.
> > +
> >   
> >   Return Value
> >   ============
> > diff --git a/Documentation/media/videodev2.h.rst.exceptions b/Documentation/media/videodev2.h.rst.exceptions
> > index 9bb9a6c..f412cc8 100644
> > --- a/Documentation/media/videodev2.h.rst.exceptions
> > +++ b/Documentation/media/videodev2.h.rst.exceptions
> > @@ -453,6 +453,7 @@ 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_LOCK_STATUS src-changes-flags
> >   
> >   replace define V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ v4l2-event-motion-det
> >   
> > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> > index 724f43e..08a153f 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -2078,6 +2078,7 @@ struct v4l2_event_frame_sync {
> >   };
> >   
> >   #define V4L2_EVENT_SRC_CH_RESOLUTION		(1 << 0)
> > +#define V4L2_EVENT_SRC_CH_LOCK_STATUS		(1 << 1)
> >   
> >   struct v4l2_event_src_change {
> >   	__u32 changes;
> Quoting from an old (July) conversation about this:
>
> > > > I'm not entirely sure I like this. Typically losing lock means that this event
> > > > is triggered with the V4L2_EVENT_SRC_CH_RESOLUTION flag set, and userspace has
> > > > to check the new timings etc., which will fail if there is no lock anymore.
> > > >
> > > > This information is also available through ENUMINPUT.
> > > >
> > > > I would need to know more about why you think this is needed, because I don't
> > > > see what this adds.
> > Hi Hans,
> >
> > At least on the ADV718x, a source resolution change (from an
> > autodetected video
> > standard change) and a signal lock status change are distinct events.
> > For example
> > there can be a temporary loss of input signal lock without a change in
> > detected
> > input video standard/resolution.
> OK, but what can the application do with that event? If the glitch didn't
> affect the video, then it is pointless.

Hi Hans, that's just it, for i.mx6 it does affect video. On i.mx6 a 
temporary
loss of signal from the adv7180 often results in a "split image", or rolling
image from captured frame to the next, and the only way to recover
from this failure is to restart the pipeline (stream off -- stream on). So
the application needs to be informed of this temporary loss of signal
event in order to restart streaming.


> If the lock is lost, then normally you loose video as well. If not, then
> applications are not interested in the event.

Yes, the lost lock causes a temporary or permanent loss of video,
but with no other indications from the adv7180 (such as a detected
video standard change). And on i.mx6, the lost lock often (actually
usually) causes a split or rolling image.

Steve