Comment # 7 on bug 1202566 from Takashi Iwai

(In reply to ted chang from comment #4)
> Created attachment 860941 [details]
> dmesg output with 0x0e
> 
>  cat /proc/cmdline 
> BOOT_IMAGE=/boot/vmlinuz-6.0.0-rc1-3.g7bd57d5-default
> root=UUID=67e5381b-1f65-49ec-9b58-2e392c6b5d9a splash=silent
> resume=/dev/disk/by-uuid/eeb7aaf9-93ab-4dc2-841a-c09ada050b9f
> mitigations=auto quiet security=apparmor drm.debug=0x0e

Thanks.  This indicated the standard backlight.

Could you test the following?
- Boot without drm.debug option, but with amdgpu.backlight=0 option.
- Verify whether you can control the backlight
- If yes, turn on the debugging
   echo 0x0e > /sys/module/drm/parameters/debug
  then go to hibernate.  Do resume, and get the dmesg output.  Turn off the
debug again
   echo 0x00 > /sys/module/drm/parameters/debug

- If the backlight isn't controlled properly with amdgpu.backlight=0 option,
try amdgpu.backlight=1 option instead.
  Then perform the same procedure as above (debug-on/hibernate/debug-off).

Upload the dmesg output taken in the test above.