Comment # 45 on bug 1180749 from Antony J.R

(In reply to Takashi Iwai from comment #42)
> The amdgpu.backlight module option was already merged in the upstream, so TW
> should have a workaround (passing amdgpu.backlight=0 boot option).  This was
> also already merged in SLE15-SP3 / Leap 15.3 kernel, too.  But I don't think
> we'd fix this for Leap 15.2.
> 
> The root cause of the problem hasn't been figured out yet.  My bet is that
> it's a BIOS bug, and more proper workarounds are needed in AMDGPU driver
> side, but this has to be sorted out in the upstream development.  Feel free
> to join to the upstream gitlab Issues.

It seems that without the amdgpu.backlight=0 kernel parameter the brightness
control is working in hybrid mode. I don't know what fixed it maybe this
https://gitlab.freedesktop.org/agd5f/linux/-/commit/f2ad3accefc63e72e9932e141c21875cc04beec8
commit.

But the brightness control seems to work good now in Linux 5.14.14 in TW.