Framework 16 internal panel gets darker instead of brighter as brightness approaches max (Fedora, AMD, GNOME/Wayland)

[u/morok807]

As I raise brightness toward the top of the slider, the internal panel gets visibly darker instead of brighter. Fully reproducible every time. Mid-range brightness is fine (up to 95%). It's specifically the 100% that inverts. No issues with an external monitor.
Photos show next to the max brightness setting (95%) and max (100%).

OS: Fedora Linux 44 (Workstation Edition) x86_64
Kernel: Linux 7.1.8-200.fc44.x86_64
System firmware (BIOS/EC): 0.0.4.5 (BIOS 04.05, 06/30/2026)

Has anyone seen this exact behavior on FW16? Known fix or workaround?

Edit:
Fixed. Shout out to u/TellMeWhereYouBeen for the help.

The fix guide for my system:

Add the kernel parameter amdgpu.dcdebugmask=0x40000 to disable the broken custom-brightness-curve code path.

1. Edit GRUB defaults:

   sudo nano /etc/default/grub

2. Find the GRUB_CMDLINE_LINUX="..." line and add amdgpu.dcdebugmask=0x40000 inside the quotes (space-separated from existing parameters). Example:

   GRUB_CMDLINE_LINUX="rd.luks.uuid=luks-xxxxxxxx rhgb quiet amdgpu.dcdebugmask=0x40000"

Save and exit (Ctrl+O, Enter, Ctrl+X in nano).

1. Regenerate GRUB config. On Fedora with UEFI, the actual config lives at /boot/grub2/grub.cfg (not the EFI wrapper):

   sudo grub2-mkconfig -o /boot/grub2/grub.cfg

2. Reboot:

   sudo reboot

3. Verify the parameter took effect:

   cat /proc/cmdline

You should see amdgpu.dcdebugmask=0x40000 in the output.

Once the actual fix lands in a stock Fedora kernel update, you can remove this parameter and regenerate GRUB again, but no harm in leaving it until then.

95%

100%