[Bug 110954] USB Type-C monitor flashes once when play a video file after unplug and re-plug the monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110954

--- Comment #20 from Stanislav Lisovskiy <stanislav.lisovskiy at intel.com> ---
(In reply to Nathan Ciobanu from comment #18)
> On Wed, Aug 21, 2019 at 08:26:34AM +0000, bugzilla-daemon at freedesktop.org
> wrote:
> > https://bugs.freedesktop.org/show_bug.cgi?id=110954
> > 
> > --- Comment #17 from Stanislav Lisovskiy <stanislav.lisovskiy at intel.com> ---
> > (In reply to Nathan Ciobanu from comment #16)
> > > On Tue, Aug 20, 2019 at 10:02:48AM +0000, bugzilla-daemon at freedesktop.org
> > > wrote:
> > > > https://bugs.freedesktop.org/show_bug.cgi?id=110954
> > > > 
> > > > --- Comment #15 from Stanislav Lisovskiy <stanislav.lisovskiy at intel.com> ---
> > > > (In reply to Nathan Ciobanu from comment #13)
> > > > > (In reply to Stanislav Lisovskiy from comment #12)
> > > > > > What do you mean by "that if you wait for the this reprobing to finish and
> > > > > > then play the video the flash will not occur"? 
> > > > > > 
> > > > > > So it does not happen once you start playback, but at some point before this?
> > > > > 
> > > > > The flash happens if you play the video (with audio) before the reprobe, If
> > > > > you play the video after reprobe it doesn't occur.
> > > > 
> > > > But when does reprobe occur? Does it occur on its own or after you replug it or
> > > > some other action?
> > > It always occurs regardless of my actions.
> > 
> > That is weird then. It should occur only once you do hotplug/change display
> > configuration. It should not happen on its own, probably that might be origin
> > of this issue.
> That is my suspicion as well. I don't know how hda behaves in MST situations
> but maybe it isn't "ready" right away when the displays finish training but
> may become "ready" a few seconds later and thus trigger a reprobe. To prove
> this which register do I need to print?
> 
> Thanks,
> Nathan
> > 
> > > 
> > > > 
> > > > -- 
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The dmesg log looks flooded with hpd irq events like this "gen8_de_irq_handler]
hotplug event received, stat 0x00400000, dig 0x10101110, pins 0x00000040, long
0x00000000", I don't think this is even related to hda, most likely there is
some issue with DP MST itself. The flash probably just happens as a result of
constant reprobing and simultaneous modeset. 
Userspace starts reprobing after it gets uevent sent by the driver in response
to hpd irq.

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