[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 #21 from Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com> ---
On Mon, Aug 26, 2019 at 09:33:04AM +0000, bugzilla-daemon at freedesktop.org
wrote:
> 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.
Does this point to the dock as a possible soure of the hpd interrupts? Do you
think the dock may have an issue? Any register we can dump to prove this? 

Thanks,
Nathan
> 
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