Arch Linux

lightofpast

Member

Registered: 2023-07-01

Posts: 4

Brightness control not working

Hi, i have a hybrid gpu laptop (intel igpu raptor lake and nvidia). I was controlling my laptop monitor brightness via nvidia_wmi_ec_backlight (/sys/class/backlight/nvidia_wmi_ec_backlight). But after resuming from suspend, the brightness went up to 100% and became uncontrollable. So i tried to use my igpu for brightness control, by adding kernel parameter acpi_backlight. I tried adding vendor and video but they didnt work. Lastly i tried acpi_backlight=native. there is /sys/class/backlight/intel_backlight now. But when i try to change the brightness, it does not change. However, if i decrease brightness level to 0, the monitor goes black completely, other than 0 it is 100% always. I am trying to find a way to control the brightness with intel gpu, any help is appreciated.

What i tried:
setting "i915.enable_dpcd_backlight=1" kernel parameter - did not work. https://wiki.archlinux.org/title/Backli … 15%20only)
disabling igpu forever -> this works even with the suspend/resume but all rendering done in the dgpu is bad for power usage

system information:
razer blade 18 2023
kernel 6.15.4-arch2-1
nvidia drivers: 575.64
mesa: 25.1.4
window manager: niri (wayland)

Last edited by lightofpast (2025-07-01 13:09:28)

unixman

Member

Registered: 2015-03-12

Posts: 115

Re: Brightness control not working

my case for kabylake iGPU (NO dGPU in this case).
opening /dev/mem and writing adress 0xb00c8254 works for me even i915(intel's kernel module) is disabled/not loaded. 

int main(int ac, char* av[]){
    int fd = open("/dev/mem", 1);
    lseek(fd, 0xb00c8254, 0);
    int val = atoi(av[1]);
    write(fd, &val, 2);

    return 0;
}

DISCLAIMER: DANGEROUS!

EDIT: memory addrs for varius intel gens can be found kernersrc/drivers/gpu/i915/*  IIRC.

Last edited by unixman (2025-07-02 22:04:13)