AMD GPU

This guide is about setting up NixOS to correctly use your Amd Graphics card if it is relatively new (aka, after the GCN architecture).

Make the kernel use the correct driver early

The kernel can load the correct driver right away (in hardware-configuration.nix):

boot.initrd.kernelModules = [ "amdgpu" ];

XServer

Make sure Xserver uses the `amdgpu` driver in your configuration.nix:

services.xserver.enable = true;
services.xserver.videoDrivers = [ "amdgpu" ];

OpenCL

Add this to your hardware-configuration.nix:

hardware.opengl.extraPackages = with pkgs; [
   rocm-opencl-icd  # NixOS Unstable
   amdappsdk  # NixOS 20.03, uses the CPU, not the GPU
];

You should also install the clinfo package to verify that Open CL is correctly setup (or check in the program you use to see if it is now available, such as in Darktable).