[Bug 97450] [SKL] [regression] Random display flickering on Kernel 4.8 with dual-screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97450

--- Comment #37 from v at robolab.it ---
(In reply to Ted from comment #15)
> I also started experiencing this issue. I've seen most of the issues
> mentioned, plus the computer would sometimes freeze (screen is black and
> caps lock light does not toggle).
> After applying the patch, I haven't had any problems yet (freezing, black
> screen, flickering).
> 
> $ lspci | grep VGA
> 00:02.0 VGA compatible controller: Intel Corporation HD Graphics 520 (rev 07)
> $ dmesg -l err -w
> [ 3221.487848] [drm:intel_pipe_update_end [i915]] *ERROR* Atomic update
> failure on pipe A (start=87034 end=87035) time 301 us, min 763, max 767,
> scanline start 753, end 768
> [ 4236.060368] tpm tpm0: A TPM error (325) occurred stopping the TPM
> [ 4236.322922] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU
> pipe B FIFO underrun
> . . . 
> The pipe underruns happen generally when I plug/unplug a monitor and/or move
> a mouse across monitor boundaries.

I'm experiencing the hard freezes too, "hard" because the system does not
respond even to REISUB, only to long pressing the Power button. I use single
display (laptop LCD), however the error messages in dmesg are similar.
Also there are screen glitches/flickering, but only if I enable the IOMMU
(check the videos there https://bugzilla.kernel.org/show_bug.cgi?id=177791 )
and they appear only when I place the mouse cursor on two exact lines of the
whole screen. 
I've thought that freezes are related to IOMMU but I got them a few times with
IOMMU disabled. Nevertheless it seems that freezes appear much more often with
IOMMU enabled than disabled.
Most of the times freezes appear when the system goes to powersave mode after
some time of inactivity when I go away from the laptop. However I got a freeze
one or two times when I was working on the laptop.
My powersave settings in KDE are: dim screen after 5 mins, switch off screen
after 10 mins, never suspend, never hibernate. Most of the times freezes appear
from 1 to (60?) minutes after the screen turns off - so from 11 minutes of
inactivity. Freezes almost never occur (just one or two times total) before the
screen turns off (in less than 10 minutes of inactivity). Sometimes the system
does not freeze even after 30 minutes of inactivity.

Despite system does not respond to REISUB, sometimes (although very rare) it is
possible to switch from the X session to the terminal session by pressing
Ctrl+Alt+F1 many times after the system freeze. 
Sometimes the terminal works fast without any problems, then I am able to log
in and see that load average stays below 1 and no processes load the CPU too
much in the 'top' or I/O in the 'iotop', but if I try to switch back to X
session with Ctrl+Alt+F7 the system completely freezes and never responds to
Ctrl+Alt+F* or REISUB.
Once after I switched to the terminal session I got an error log to console
stating about 'i915' so I think the problem is related to the powersave of
Intel integrated GPU. Please see the photo here:
http://robolab.it/iommu/call_trace.jpg
This time I was not able to login as the system got completely frozen after I
typed 'root'.

I use Clevo P640RE with Core i7-6700HQ CPU, openSuSE 13.2 with kernel 4.8.1
installed from this repo:
http://download.opensuse.org/repositories/Kernel:/stable/standard/

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