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" ];

Enable Southern Islands (SI) and Sea Islands (CIK) support

The linux package enables AMDGPU support Southern Island (si) and Sea Island(cik). You can set kernel params to enable support

# for Southern Islands (SI) cards
boot.kernelParams = [ "radeon.si_support=0" "amdgpu.si_support=1" ];
# for Sea Islands (CIK) cards
boot.kernelParams = [ "radeon.cik_support=0" "amdgpu.cik_support=1" ];

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

To enable vulkan

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

Note: amdvlk is not needed for vulkan

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 
# Only available on unstable
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

Problems

Dual Monitors

If you encounter problems having multiple monitors connected to your gpu, adding `video` parameters for each connector to the kernel command line sometimes helps.

For example:

boot.kernelParams = [
    "video=DP-1:2560x1440@144"
    "video=DP-2:2560x1440@144"
];

Of course you have to adjust the connector names (like `DP-1`), the resolution and frame rate accordingly.

To figure out your connector names, use:

head /sys/class/drm/*/status

with your monitors connected.