Arch Linux

maldus

Member

Registered: 2017-03-20

Posts: 28

Backlight always at 100% on X

Hello everyone,
I've been plagued by this problem for a while now. Since updating my Nvidia driver to anything >465, brightness control has stopped working on my laptop. I've been putting off updating my system until today, hoping that it would have randomly fixed itself in the latest driver. It didn't.

Premises:
- Clevo p750tm laptop
- Arch linux, fully updated (Linux nadja 6.1.1-arch1-1 #1 SMP PREEMPT_DYNAMIC Wed, 21 Dec 2022 22:27:55 +0000 x86_64 GNU/Linux)
- NVIDIA Geforce GTX 1060
- systemd-boot (not sure if relevant)
- Qtile (X11) window manager

What happens:
Up until the login screen, before starting X11, everything works. I have `/sys/class/backlight/acpi_video0/` and can write to the corresponding `brightness` file to change the backlight. It works.
When I start Qtile a new contender appears under `/sys/class/backlight/nvidia_0`, but the screen brightness is stuck at 100%. I can change it manually or by third party tools like xbacklight or brightnessctl and the content of `brightness` changes accordingly, but the light doesn't fade.

It's probably relevant to include

cat /usr/share/X11/xorg.conf.d/10-nvidia-drm-outputclass.conf
───────┬────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: /usr/share/X11/xorg.conf.d/10-nvidia-drm-outputclass.conf
───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ Section "OutputClass"
   2   │     Identifier "nvidia"
   3   │     MatchDriver "nvidia-drm"
   4   │     Driver "nvidia"
   5   │     Option "AllowEmptyInitialConfiguration"
   6   │     ModulePath "/usr/lib/nvidia/xorg"
   7   │     ModulePath "/usr/lib/xorg/modules"
   8   │ EndSection

Right now, the only kernel command line option I'm using is `acpi_backlight=video`. With other options the `acpi_video0` device never appears and I have no way to change the backlight, ever.

Can anyone please guide me to diagnose and possibly fix this problem?

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 21,707

Re: Backlight always at 100% on X

Have you tried changing the backlight without that parameter but with X started? FWIW Backlight handling native to nvidia is relatively new, afaik there should be a kernel parameter you could try to disable but I'm unable to find it googling and not on my arch to look at the module itself, look for related parameters in

modinfo nvidia
modinfo nvidia-drm

and the like.

maldus

Member

Registered: 2017-03-20

Posts: 28

Re: Backlight always at 100% on X

I have now; no difference. I've heard of this parameter before, could it be what you were thinking of?

nvidia.NVreg_RegistryDwords=EnableBrightnessControl=1

I have tried with this parameter and the option both to 1 and 0, no difference.