[Bug 109246] HDMI connected monitors fail to sleep and instead turn back on when amdgpu.dc=1

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109246

--- Comment #10 from Alex Deucher <alexdeucher at gmail.com> ---
(In reply to Michel Dänzer from comment #8)
> 
> This does look like there are hotplug events, and the HDMI output is
> considered disconnected for a moment.

When the monitor enters dpms, it starts polling inputs so it can light up
whatever input gets connected without the user having to manually select the
input.  This can cause havoc with drivers sometimes.

> 
> (In reply to Alex Deucher from comment #5)
> > Some monitors poll inputs which sometimes causes the hpd pin to fire which
> > looks like a hotplug event to the driver.
> 
> Any idea why this seems to only cause trouble with DC though?

DC handles both short and long pulses while I think the non-DC code only
handles long pulses.  IIRC, the only difference is the length of the pulse and
I think the register values used to determine the pulse length are tuned
slightly differently in DC to deal with other problematic monitors.  I suspect
tuning those settings would fix the issue, but I don't know if it would break
other things.

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