NixOS has iGPU and dGPU mixed up

Help
1

I’m using the COSMIC DE with Wayland on a T2 Macbook Pro (16,1) - it has an Intel UHD 630 iGPU and an AMD 5500M dGPU. The system recognizes both of these, but it thinks that the Intel GPU is the discrete card:

igpu-mixup
igpu-mixup2137×1363 380 KB

I’ve tried several solutions to change this, but every time it causes the dGPU to hang, overheat, and cause the system to freeze.

What is causing this, and how do I fix it? As it stands I get hardly any battery life because the system is constantly using the AMD card since it thinks that’s the integrated card.

2

maybe relevant Introduction - t2linux wiki

3

Wayland compositors usually take on the system’s boot GPU as the primary one by default. You could maybe flip this in BIOS.

Other than that, configuration is completely up to the compositor. I don’t know how much of GNOME survives in COSMIC, but there a udev rule like this would be used:

services.udev.packages = [
  (pkgs.writeTextDir "lib/udev/rules.d/62-gnome-gpu-priority.rules" ''
    SYMLINK=="dri/igpu1", TAG+="mutter-device-preferred-primary"
  '');
}

… replacing dri/igpu1 with an appropriate reference to your real iGPU, usually in dri/by-path/pci-, you can browse those paths under /dev and get some hints with lspci.

If COSMIC does not retain enough GNOME for that to just work, I’d suggest asking on COSMIC-related forums. This stuff is hidden deep in the code, and I don’t have the patience to read theirs.