[Solved?] AMD CPU/GPU backlight brightness issues since updates

Horghski · 2025-07-16 13:44:37

seth wrote:

Does it also happen if you only boot the rescue.target (2nd link below)?
Typically systemd should™ restore the previous backlight level and unless you're crossing kernel versions (between before and after amd got funny) the absolute value should™ not matter, so rather remove systemd.restore_state=0 if that's not your situation.
If nothing else helps
seth wrote:
You could add a service that runs brightnessctl w/ some predefined percentage or re/stores one via it instead.

I'm having a senior moment, what rescue target and what 2nd link? I don't jump kernel versions, I just have the latest kernel that I boot into every time, and the LTS kernel as a backup that I haven't had to use (yet).

I can remove the restore kernel flag and test again. Right now I have brightnessctl in my .bashrc which is good enough, but if that's what I have to do long term, then yes, I'll add a service.

seth · 2025-07-16 14:02:09

2nd link in my signature to http://wiki.archlinux.org/title/Systemd … _boot_into (it also explains the rescue.target)

Horghski · 2025-07-16 20:43:18

Ok, so I removed the systemd.restore line from my kernel parameters, keeping the amdgpu parameter, and now the brightness automagically restores on boot on battery. So I guess for me at least the fix is the amdgpu parameter? Either way, thank you for your help sir.

p0358 · 2025-07-17 22:48:48

Had the same issue after update on my Acer AMD laptop (with HDR panel and LUKS encryption). Turns out I needed to add both "amdgpu.dcdebugmask=0x40000" and "systemd.restore_state=0" to kinda fully get it to previous behavior (being on kernel 6.15.6-zen1-1-zen right now).

The situation was as follows:

No kernel params: screen goes black shortly after password prompt shows up, never lights up again (well, at least not while in SDDM?)
"amdgpu.dcdebugmask=0x40000" added: the screen goes black shortly after password prompt shows up, but after blindly typing the password in, in a few moments the boot log and then SDDM is visible again
Both kernel params: the screen goes black for one second after password is shown, kinda like before, then it lights back on (but seemingly with lower brightness than what it used to be, not 100%, and there's a few kernel log spams about ACPI that didn't use to be shown, maybe random and unrelated?), then it keeps being lit up. I think late boot log, SDDM and then KDE would just about correctly have my previous backlight level of about 25%.

The tests were done with charger plugged in, so perhaps I'm yet to discover it being broken on battery, who knows.

Also isn't this some userspace bug that it gets so confused about brightness range change that it ends up at 0? Or does it try to restore something akin to last setting in range of 0-255, except 255 is now about 1.5%? But I tried looking really close up and really didn't see any image on that black screen (it's OLED if it matters, I know on some older panel technologies you could flash external light onto a panel with broken backlight to see something, but perhaps not the case with OLED?). Just my 3 cents.

seth · 2025-07-18 05:06:45

Or does it try to restore something akin to last setting in range of 0-255, except 255 is now about 1.5%?

It would seem that systemd restores the absolute value, yes.
You'd then get this once (every time you cross the change with kernels) - doesn't sound like the robustest approach (max backlight to calculate percentages is available, nothing userspace could do about the more "natural" backlight curve, ie. what that percentage means)
Feel free to file a bug against systemd…

Arch Linux

#26 2025-07-16 13:44:37

Re: [Solved?] AMD CPU/GPU backlight brightness issues since updates

#27 2025-07-16 14:02:09

Re: [Solved?] AMD CPU/GPU backlight brightness issues since updates

#28 2025-07-16 20:43:18

Re: [Solved?] AMD CPU/GPU backlight brightness issues since updates

#29 2025-07-17 22:48:48

Re: [Solved?] AMD CPU/GPU backlight brightness issues since updates

#30 2025-07-18 05:06:45

Re: [Solved?] AMD CPU/GPU backlight brightness issues since updates

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