https://bugs.freedesktop.org/show_bug.cgi?id=107045

--- Comment #22 from taijian@posteo.de ---
OK, after some further testing, here is some more information on my issue:

1) It turns out that the crashing/hanging behaviour ONLY happens when I'm
logged into a graphical session (GNOME in my case). When working exclusively
from a tty, then the system remains stable.

2) A Wayland session seems to be slightly more stable/resillient to crashing
than an X11 session. While the latter crashes almost immediately when doing
anything with the backlight, the former goes through a couple of cycles of
extreme lag, stuttering and recovery before finally succumbing to whatever the
problem is.

3) I can reliably and reproduceably crash my graphical session by messing with
screen brightness in any way - either through the tools of the graphical shell
or by doing #echo X > /sys/class/backlight/intel_backlight/brightness.

4) Why is this an amdgpu bug then? Because the issue only arises when amdgpu is
loaded in DC mode, because in this mode the display connectors directly
connected to the dGPU (DP, eDP and HDMI) are being ennumerated. With dc=0 they
are not recognized and can therefore not create any problems.

5) What I think happens is that the graphical shell tries to adjust brightness
on the displays that are ennumerated as connectors but not actually connected,
and by doing so eventually get amdgpu to crash irrecoverably. 

6) When intel_backlight gets manipulated, the following always shows up in
dmesg (the first couple of times the dGPU gets to the 'reset', at some point is
just crashes before that, taking the system with it).


Aug 31 17:58:54 alien-arch kernel: [drm] PCIE GART of 256M enabled (table at
0x000000F400000000).
Aug 31 17:58:54 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 62 ret is 0 
Aug 31 17:58:54 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:58:55 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 18f ret is 0 
Aug 31 17:58:55 alien-arch kernel: [drm] UVD and UVD ENC initialized
successfully.
Aug 31 17:58:55 alien-arch kernel: [drm] VCE initialized successfully.
Aug 31 17:58:56 alien-arch kernel: [drm] Cannot find any crtc or sizes
Aug 31 17:58:57 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 15b ret is 0 
Aug 31 17:58:58 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 155 ret is 0 
Aug 31 17:59:06 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 281 ret is 0 
Aug 31 17:59:07 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:59:07 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 261 ret is 0 
Aug 31 17:59:08 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:59:08 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 261 ret is 0 
Aug 31 17:59:09 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:59:10 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 261 ret is 0 
Aug 31 17:59:10 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:59:11 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 261 ret is 0 
Aug 31 17:59:12 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:59:12 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 261 ret is 0 
Aug 31 17:59:13 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:59:13 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 261 ret is 0 
Aug 31 17:59:14 alien-arch kernel: amdgpu: [powerplay] 
                                    last message was failed ret is 0
Aug 31 17:59:14 alien-arch kernel: amdgpu: [powerplay] 
                                    failed to send message 261 ret is 0 
Aug 31 17:59:14 alien-arch kernel: amdgpu 0000:01:00.0: GPU pci config reset

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