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

From 20.09, add this to your hardware-configuration.nix:

hardware.opengl.extraPackages = with pkgs; [
   rocm-opencl-icd
   rocm-opencl-runtime
];

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).

Vulkan

hardware.opengl.driSupport = true;
# For 32 bit applications
hardware.opengl.driSupport32Bit = true;

Starting from 20.09, the amdvlk drivers can be used in addition to the mesa radv drivers, the program will choose which one to use:

hardware.opengl.extraPackages = with pkgs; [
   amdvlk
];
# For 32 bit applications
hardware.opengl.extraPackages32 = with pkgs; [
  driversi686Linux.amdvlk
];

more information can be found here https://nixos.org/manual/nixos/unstable/index.html#sec-gpu-accel-vulkan