Unable to boot 5.18-rc kernel on amdgpu legacy (si) hardware.

[Paul Blazejowski]

Hello,

I am unable to boot 5.18-rc1(2) kernel with my rather old (si) XFX card, 
which works fine under 5.17.3 and previous kernels.

The card is identified as:

1:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] 
Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]

Running on a Asus M5A99FX PRO R2.0 mainboard.

The boot process stops at "fb0: EFI VGA frame buffer device" step and 
the hdmi connected monitor just shuts off, there's not oops or any other 
debug output captured by serial console.

I was able to bisect the kernel tracing this to a bad commit:

git bisect bad 3712e7a494596b26861f4dc9b81676d1d0272eaf
# first bad commit: [3712e7a494596b26861f4dc9b81676d1d0272eaf] 
drm/amd/pm: unified lock protections in amdgpu_dpm.c

And reverting this commit on 5.18-rc2 kernel makes my system bootable again.

Please let me know if there's anything else i could provide to help fix 
this issue. I have access to serial console if needed.

Thank you.