Please include you dmesg output and xorg log if using X.  The default setting of amdgpu.ppfeaturemask should be safe.  Is there a specific feature you are trying to enable by forcing it?

Created attachment 142681 [details]
xorg log with ppfeaturemask=0xffffffff

Created attachment 142682 [details]
dmesg with 4.20.0-rc4 kernel when having the issue

As I understand, ppfeaturemask is set in order to enable manual performance level configuration and overclocking (more importantly, the archwiki says thats what it does, so people will do it).

I've intermittently had this issue with the 4.18 and 4.20rc* kernels with my rx 580 (I've mostly been running the 4.14lts kernel, but that has different issues). Manually setting performance level prevents flickering and artifacting I see on herbstluftwm (which I coudln't reproduce on openbox).

(In reply to echarlie from comment #3)
> Created attachment 142682 [details]
> dmesg with 4.20.0-rc4 kernel when having the issue
> 
> As I understand, ppfeaturemask is set in order to enable manual performance
> level configuration and overclocking (more importantly, the archwiki says
> thats what it does, so people will do it).
> 
> I've intermittently had this issue with the 4.18 and 4.20rc* kernels with my
> rx 580 (I've mostly been running the 4.14lts kernel, but that has different
> issues). Manually setting performance level prevents flickering and
> artifacting I see on herbstluftwm (which I coudln't reproduce on openbox).

if you dont need overclock per se you can still use manual settings without changing default ppfeaturemask

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