[Intel-gfx] Panic after S3 resume and modeset with MST

[Lyude Paul]

Hi! Just an FYI I am planning on taking a look at this very soon

On Mon, 2017-03-27 at 18:02 +0200, Takashi Iwai wrote:
> Hi,
> 
> the upstream fix a16b7658f4e0d4aec9bc3e75a5f0cc3f7a3a0422
>     drm/i915: Call intel_dp_mst_resume() before resuming displays
> 
> seems to trigger a kernel panic when some modeset change happens
> after
> S3 resume.  The details are found in openSUSE bugzilla,
>   https://bugzilla.suse.com/show_bug.cgi?id=1029634
> 
> In short, the following procedure causes a kernel panic (supposedly)
> almost 100% on Dell Latitude with Skylake with MST DP on dock:
> 
> - Boot with a docking station, DP-1 connected.
> - Login on X
> - xrandr --output eDP-1 --primary --auto --output DP-1-1 --auto --
> left-of eDP-1
>   ==> This changes the mode.
> - Suspend ("systemctl suspend" in my case), and close the lid.
> - Remove from the dock (keep the lid closed).
> - Open the lid, which resumes automatically.  It works.
> - Suspend again.
> - Connect to the dock again (keep the lid closed).
> - Open the lid, which resumes automatically.  It's still OK.
> - xrandr --output eDP-1 --primary --auto --output DP-1-1 --auto --
> left-of eDP-1
>   ==> Now the kernel feezes.
> 
> Reverting the commit mentioned above fixes the problem.
> 
> The problem is present in all versions I tested.  The reported kernel
> in the Bugzilla is 4.4.x-based one, but the issue is seen in 4.11-
> rc3,
> too.  Note that the S3 resume itself works in 4.11-rc3; the kernel
> panic happens when invoking xrandr manually after that.
> 
> Unfortunately, I couldn't get a kernel panic message, so far.  kdump
> didn't work well in this case by some reason.  There are some
> screenshots taken by the original reporter (could switch VT
> beforehand), but I don't know whether it helps.
> 
> If you have any hints for further debugging, it'd be highly
> appreciated.
> 
> 
> thanks,
> 
> Takashi