https://bugzilla.kernel.org/show_bug.cgi?id=210263
--- Comment #8 from ninelore@protonmail.com --- (In reply to Fabian from comment #5)
As of Kernel 5.15, I don't need fbcon=nodefer anymore. By default the backlight works and is set on start. I still get from time to time an boot-error by systemd, but that can be also worked around by loading amdgpu early.
Can someone confirm this?
(In reply to jaromir.obr from comment #6)
@Fabian I have the same experience. I was running kernel 5.13 on Ubuntu 21.10 and when I upgraded to mainline kernel 5.15.13 (using https://github.com/pimlie/ubuntu-mainline-kernel.sh), the service "systemd-backlight@backlight:amdgpu_bl0.service" starts as expected and backlight seems to be restored.
With kernel 5.13 it failed: "Failed to start Load/Save Screen Backlight Brightness of backlight:amdgpu_bl0" and I was not able to start it manually.
Can confirm this bug is fixed with 5.15