[Bug 102322] System crashes after "[drm] IP block:gmc_v8_0 is hung!" / [drm] IP block:sdma_v3_0 is hung!

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102322

--- Comment #37 from dwagner <jb5sgc1n.nya at 20mm.eu> ---
In the related bug report (https://bugs.freedesktop.org/show_bug.cgi?id=107152)
I noticed that this bug can be triggered very reliably and quickly by playing a
video with a deliberately lowered frame rate:
 "mpv --no-correct-pts --fps=3 --ao=null some_arbitrary_video.webm"

This led me to assume this bug might be caused by the dynamic power management,
that often ramps performance up/down when a video is played at such a low frame
rate.

And indeed, I found this confirmed by many experiments: If I use a script like
> #!/bin/bash
> cd /sys/class/drm/card0/device
> echo manual >power_dpm_force_performance_level
> # low
> echo 0 >pp_dpm_mclk 
> echo 0 >pp_dpm_sclk
> # medium
> #echo 1 >pp_dpm_mclk 
> #echo 1 >pp_dpm_sclk
> # high
> #echo 1 >pp_dpm_mclk 
> #echo 6 >pp_dpm_sclk
to enforce just any performance level, then the crashes do not occur anymore -
also with the "low frame rate video test".

So it seems that the transition from one "dpm" performance level to another,
with a certain probability, causes these crashes. And the more often the
transitions occur, the sooner one will experience them.

(BTW: For unknown reason, invoking "xrandr" or enabling a monitor after sleep
causes the above settings to get lost, so one has to invoke above script
again.)

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