Screen too dark at high brightness on kernel 6.14+ (BOE / AMD iGPU)

seikabook · 2026-08-07 13:23:45

Since upgrading to a 6.14+ kernel my laptop screen gets *darker* as I raise
the brightness toward maximum, instead of brighter. Backlight sysfs values
look correct (actual_brightness near max) but the panel is visibly dim.

Hardware:
- Panel: BOE NE160QDM-NY3 (eDP, 2560x1600)
- GPU: AMD Ryzen 7 8845HS (780M, amdgpu)
- Kernel: 6.15 / 7.1.6, amdgpu 3.64.0

Root cause:
Since Linux 6.14, amdgpu may apply a panel's "custom brightness curve"
parsed from the panel's EDID luminance data. On this panel the interpolation
is wrong, so high brightness steps map to a dimmer backlight.
Confirm with:
journalctl -b -k | grep -i "custom brightness curve"
You'll see: `[drm] Using custom brightness curve`

Fix (workaround, recommended by AMD):
Add the following kernel parameter to disable the custom curve:
amdgpu.dcdebugmask=0x40000
Then regenerate the bootloader config. On GRUB:
sudo grub-mkconfig -o /boot/grub/grub.cfg
Reboot. Brightness now scales linearly and max is actually max.

If you get screen flicker after this, use 0x40410 instead (also disables
PSR / Panel Self Refresh):
amdgpu.dcdebugmask=0x40410

This is a per-panel quirk; the proper fix is upstream (AMD adding a quirk
for this BOE panel). See linked bug report. Marking solved with the
workaround.

seth · 2026-08-07 17:34:39

Your LLM got that from the wiki before it was flagged for removal in march - https://wiki.archlinux.org/index.php?ti … did=868368
Is this actually still a problem w/ 6.18?
Why are you running a dated kernel (6.15) - is this even archlinux?

seikabook · 2026-08-08 04:33:51

My bad — it was the 6.1 ISO, kernel now at 7.1.6, and zen/LTS hit the same bug. It first showed up on the 8.1 image at boot and I couldn't nail it down, so I reinstalled with 6.1. The kernel upgrade brought it back, which is how I finally located it.

seth · 2026-08-08 05:36:36

If this is an ongoing problem you'd need to raise that at the wiki (to restore the removed paragraph) - posting PSAs in the forum is pointless as they will get lost in time in space.
PSR is still addressed, https://wiki.archlinux.org/title/AMDGPU … timed_out)

Arch Linux

#1 2026-08-07 13:23:45

Screen too dark at high brightness on kernel 6.14+ (BOE / AMD iGPU)

#2 2026-08-07 17:34:39

Re: Screen too dark at high brightness on kernel 6.14+ (BOE / AMD iGPU)

#3 2026-08-08 04:33:51

Re: Screen too dark at high brightness on kernel 6.14+ (BOE / AMD iGPU)

#4 2026-08-08 05:36:36

Re: Screen too dark at high brightness on kernel 6.14+ (BOE / AMD iGPU)

Board footer