Re: [PATCH v5 15/39] [media] v4l2: add a frame interval error event

[Steve Longerbeam]

On 03/11/2017 10:51 AM, Russell King - ARM Linux wrote:
> On Sat, Mar 11, 2017 at 10:14:49AM -0800, Steve Longerbeam wrote:
> > On 03/11/2017 03:39 AM, Hans Verkuil wrote:
> > > It's fine to use an internal event as long as the end-user doesn't
> > > see it. But if you lose vsyncs, then you never capture another frame,
> > > right?
> >
> > No, that's not correct. By loss of vertical sync, I mean the IPU
> > captures portions of two different frames, resulting in a permanent
> > "split image", with one frame containing portions of two consecutive
> > images. Or, the video rolls continuously, if you remember the old CRT
> > television sets of yore, it's the same rolling effect.
>
> I have seen that rolling effect, but the iMX6 regains correct sync
> within one complete "roll" just fine here with IMX219.  However, it
> has always recovered.
>
> So, I don't think there's a problem with the iMX6 part of the
> processing, and so I don't think we should cripple the iMX6 capture
> drivers for this problem.

And there is no crippling going on. Measuring the frame intervals
adds very little overhead.

Steve