Brightness broken on ASUS OLED laptop with Intel ARC GPU (with workaround)

[mlabbe]

System details

ASUS ROG G16 GU605CM, Intel Arc (i915 driver, Arrow Lake-P, PCI ID 8086:7D51), NVIDIA RTX 5060 hybrid

What's wrong?

Problem: rolling update caused brightness controls on Asus laptop to stop working.

Panel: Panel: OLED eDP on card0-eDP-2, missing HDR static metadata in EDID

After rolling update to kernel 7.1.3, intel_backlight sysfs node exists and accepts writes but has no visual effect

Kernel dmesg explicitly diagnoses it and recommends the fix:

i915 0000:00:02.0: [drm] [CONNECTOR:508:eDP-2] Panel is missing HDR static metadata.
Possible support for Intel HDR backlight interface is not used.
If your backlight controls don't work try booting with i915.enable_dpcd_backlight=3.

The fix should be added to Omarchy's hardware-specific kernel parameter handling for GU605CM and likely all GU605-series OLED models (GU605MV, GU605MI, GU605CR, GU605CX share the same panel family)

# add the parameter
sudo nano /etc/default/limine

# now rebuild
sudo pacman -S --noconfirm linux

Omarchy Maintainers: Highly recommend adding hardware detection and setting the kernel parameter directly.

lspci reports the Intel Arc GPU is 0300: 8086:7d51.

3: "try HDR backlight first, fall back to standard DPCD"