[Bug 89461] [BSW] replug HDMI/DP cable does not light up screen sometimes

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89461

--- Comment #15 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Jeff Zheng from comment #14)
> Created attachment 116342 [details]
> dmesg with i915.disable_power_well=0
> 
> This dmesg is generated with:
> 1. Boot with both eDP and DP connected
> 2. xinit &
> 3. unplug DP
> 4. Plug in DP cable, DP monitor is black screen.

You have no userspace to react to the HPDs so the link remains up even if the
cable gets disconnected. I suppose there are two options
a) the sink went into D3, although IIRC this would be against the spec (sink is
required to enter D0 on full HPD).
b) the sink just doesn't feel that the link is up and running. Can't recall if
there's anything in the spec about what should happen on the sink end when the
cable is disconnected.

So while the test scenario is a bit bogus it would be interesting to see what
the sink is thinking in this case. I'll attach a debug patch for that...

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