Gammastep fails to set gamma LUT in wayland on i915 (12th gen Intel graphics)

Hi there,

I realise this error might not be related to NixOS itself but thought I’d start here for some troubleshooting advice.

I’m running the latest NixOS unstable with sway 1.8/wlroots 1.15.1, and getting the following error logged by sway when trying to run gammastep -O 3500K:

00:39:25.833 [ERROR] [wlr] [backend/drm/legacy.c:221] Failed to set gamma LUT on CRTC 80: Function not implemented

Nothing related shows up in dmesg.

I’m booting with the i915.force_probe kernel parameter set as described here.

Not sure how to start narrowing down which part of the stack is responsible for this issue, any advice would be much appreciated. Does i915 just not support gamma LUT setting on this device at all?

lshw -c display output in case it is helpful:

       description: i915drmfb
       physical id: 2
       bus info: pci@0000:00:02.0
       logical name: /dev/fb0
       version: 0c
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm bus_master cap_list rom fb
       configuration: depth=32 driver=i915 latency=0 mode=2256x1504 visual=truecolor xres=2256 yres=1504
       resources: iomemory:600-5ff iomemory:400-3ff irq:201 memory:605c000000-605cffffff memory:4000000000-400fffffff ioport:3000(size=64) memory:c0000-dffff memory:4010000000-4016ffffff memory:4020000000-40ffffffff

D’oh - it was a silly oversight in the end. Looks like I was on the 5.15 LTS kernel without realising. Upgraded to the latest kernel by adding boot.kernelPackages = pkgs.linuxPackages_latest; to my configuration.nix and that solved the issue. I’m new to NixOS so I assumed just upgrading to nixos-unstable channel would automatically upgrade the kernel too. Will leave this here in case it helps anyone in the same situation.