Brightness cannot be set when using Nvidia dGPU on ASUS Laptop

Ask Fedora
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1

I’ve just installed nvidia driver for my dGPU NVIDIA GeForce RTX 5070 Max-Q / Mobile [Discrete] on my laptop, and it didn’t use my dGPU as the default gpu until I disable amd iGPU in the BIOS. Since then the screen backlight cannot be set with either kde brightness controller or changing figures in files in /sys/class/backlight.

I’ve tried adding acpi_backlight=video to the kernel parameter but still brightness cannot be set.

Also I’m using an ASUS laptop, if that helps.

Could anyone kindly help me with it?

Adding that I’m using wayland.

2

Tthere are several different parameter you can pass to the kernel to tell it how to control backlight.

acpi_backlight= [HW,ACPI]
                        { vendor | video | native | none }
                        If set to vendor, prefer vendor-specific driver
                        (e.g. thinkpad_acpi, sony_acpi, etc.) instead
                        of the ACPI video.ko driver.
                        If set to video, use the ACPI video.ko driver.
                        If set to native, use the device's native backlight mode.
                        If set to none, disable the ACPI backlight interface.

Try the others if you have not already.

4

Thank you for the suggestion!

I’ve tried all three options other than none and the brightness still won’t work.

Curious things have come out when I run lsmod | grep ‘backlight’

nvidia_wmi_ec_backlight 12288 0
drm_panel_backlight_quirks 12288 1 amdgpu
video 81920 5 nvidia_wmi_ec_backlight,asus_wmi,amdgpu,asus_nb_wmi,nvidia_modeset
wmi 32768 4 video,nvidia_wmi_ec_backlight,asus_wmi,wmi_bmof

Wonder if that means anything.

Also when no manual settings on acpi_backlight parameters there’s only one folder called nvidia_wmi_ec_backlight under /sys/class/backlight/ if my memory’s correct, and when it’s set to video I get two called something involving either “video0” or “video1”. When it’s set to vendor nothing’s in the /sys/class/backlight/ path. Hope this helps.

5

I’ve figured it out somehow!

As I mentioned I’m using an ASUS laptop so I followed the instruction “Custom ROG kernel” in this manual https://asus-linux.org/guides/fedora-guide/ switching into cachyos kernel which seem to have been modified with relevant patches.

After that the brightness still won’t work. It was until I set acpi_backlight=native that everything works. So, my theory is that the custom patched kernel + acpi_backlight=native solves these problems on ASUS laptops. Hope this would be of help to friends with similar situations.

Additionally following that guide I installed asusctl, supergfxctl and also asusctl-rog-gui, although to my belief none of them helps solve my problem.