Regression in 6.6: trying to set DPMS mode kills radeon (r600)

[Holger Hoffstätte]

On 2023-12-16 18:36, Holger Hoffstätte wrote:

<snip>
> The affected machine is an older SandyBridge dektop with a fanless
> r600 Redwood GPU, using the radeon driver. "Recently" - some time
> after the last few 6.6.x stable updates - it started to die with GPU
> lockups. I first blamed this on standby/resume - because why not? - but
> this turned out to be wrong; the real culprit is DPMS.
> 
> I use xfce-power-manager as "screensaver" to turn off the display after
> inacitvity. This can be configured in two ways: "suspend" and "poweroff".
> I've been using "poweroff" since forever without problems, until now.
> 
> The symptom is that everything works fine until the screensaver kicks in
> and tries to turn the monitor off, which sends the radeon driver and the GPU
> into a complete tailspin.

<snip>

> Eventually the screensaver tries to switch off the monitor via DPMS "poweroff" method and
> this greatly upsets the GPU:
> 
> Dec 12 20:39:59 ragnarok kernel: radeon 0000:01:00.0: ring 0 stalled for more than 10140msec
> Dec 12 20:39:59 ragnarok kernel: radeon 0000:01:00.0: GPU lockup (current fence id 0x0000000000000002 last fence id 0x0000000000000003 on ring 0)

In the meantime I have confirmed that all this is still more complicated:
even using the "suspend" method only works after boot, not after a system suspend
cycle. Yes, weird but reproducible.

I have tried to chase down the problematic release, and as suspected this
started to happen with 6.6.5; 6.6.4 is fine.

Based on this information I found the offending commits and reverted them
in order from 6.6.7, which fixes everything for me:

b0399e22ada0 "drm/amd/display: Remove power sequencing check"
45f98fccb1f6 "drm/amd/display: Refactor edp power control"

Suggestions on how to proceed would be appreciated. I can report this
to  -stable and request reverts, but wanted to check with the list first.

Thanks,
Holger