systemd-backlight does not save and restore brightness for nvidia display

[Bump]

Running nvidia gtx 1080 graphics card, with proprietary nvidia drivers on ubuntu 19.04. I can change screen brightness from 0% to 100% in 5% steps. However, after a reboot or after a shutdown, brightness level reverts to 100%. Please fix to is "remembers" the current brightness value at shutdown time, like in does Windows.

[Bump (bump55)]

Happens on both ubuntu and Plasma.

[Bump (bump55)]

$ cat /sys/class/backlight/nvidia_0/actual_brightness
85
$ cat /sys/class/backlight/nvidia_0/max_brightness
100

[Bump (bump55)]

/lib/systemd/system/systemd-backlight@.service NOT working properly with nvidia cards.

[Bump (bump55)]

systemctl list-units --no-pager |grep "systemd-backlight"
  systemd-backlight@backlight:acpi_video0.service loaded active exited Load/Save Screen Backlight Brightness of backlight:acpi_video0
  systemd-backlight@backlight:nvidia_0.service loaded active exited Load/Save Screen Backlight Brightness of backlight:nvidia_0

[Bump (bump55)]

The notebook has 2 gpus, one is from the intel cpu and another is nvidia which can be enabled or disable on bios on section "MSI VGA MODE" and choose "MSI IGPU MODE" or "MSI DGPU MODE"

[Kai-Heng Feng (kaihengfeng)]

The backlight device only gets registered after it's opened by graphical session.

And the backlight gets unregistered when graphical session stops, hence when systemd-backight@.service's "Conflicts=shutdown.target" triggers, the backlight is already gone so the brightness wasn't saved.

Since it's not saved, the backlight won't be restored for next boot.

The easiest approach is to let nvidia driver always registers the backlight device.

[Bump (bump55)]

Well, apparently Nvidia driver doesn't do that.

[D (djve)]

And it's an issue with 20.04 daily builds.
Hardware is Lenovo P73 with NVIDIA RTX-5000 Q-Max.

So how can the driver be made to register the backlight device?

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Bump (bump55)]

Has anybody checked how other distros operate this? Maybe Debian/Kali?

[Ayush Akarsh (ayush-akarsh)]

I have a nvidia 1650 graphic card on my legion-Y540 with ubuntu 20.04
I had fixed my brightness issue(Function keys not working) by adding Option "RegistryDwords" "EnableBrightnessControl=1" in the device section of /etc/x11/xorg.conf

It worked perfectly well until a software update, then now method worked, and I am only able to adjust brightness with the help of brightness controller, but in that I cannot use night mode, cause it sets the brightness to maximum only, whenever I use that.

Please help!!

[Bump (bump55)]

@ayush-akarsh try this command to get and set backlight. Works for me on nvidia.

xbacklight -get
xbacklight -set 40