Displaylink

DisplayLink monitors

In order to use DisplayLink monitors over USB, such as the ASUS MB16AC, the DisplayLink driver needs to be installed.

Since these drivers depend on binary unfree blobs, you will need to first add it to your Nix store.

Run nix-shell -p displaylink --arg config '{ allowUnfree = true; }' to get the instructions and follow them.

When you try to use pkgs.displaylink in your nixos system, you will get the same instructions printed to the stderr, follow those to prefetch the driver. Once the blob is in the Nix store you can add the package

environment.systemPackages = with pkgs; [
 displaylink
];

Then add the videoDrivers:

services.xserver.videoDrivers = [ "displaylink" "modesetting" ];

The module nixos/modules/hardware/video/displaylink.nix should also work for wlroots compositors.

Connecting a second external monitor

In order to add a second external monitor you can add the following to your configuration:

services.xserver.displayManager.sessionCommands = ''
    ${lib.getBin pkgs.xorg.xrandr}/bin/xrandr --setprovideroutputsource 2 0
'';

Sway

Identify which card has the render device, evdi is the DisplayLink interface, so it's not card0, but card1.

$ ls -l /dev/dri/by-path
lrwxrwxrwx - root  2 Nov 13:38 pci-0000:00:02.0-card -> ../card1
lrwxrwxrwx - root  2 Nov 13:38 pci-0000:00:02.0-render -> ../renderD128
lrwxrwxrwx - root  2 Nov 13:38 platform-evdi.0-card -> ../card0

environment.variables = {    
  WLR_EVDI_RENDER_DEVICE = "/dev/dri/card1";                                                                                                   
};
nixpkgs.overlays = [
  (final: prev: {    
    wlroots_0_17 = prev.wlroots_0_17.overrideAttrs (old: { # you may need to use 0_18
      patches = (old.patches or [ ]) ++ [
        (prev.fetchpatch {
          url = "https://gitlab.freedesktop.org/wlroots/wlroots/uploads/bd115aa120d20f2c99084951589abf9c/DisplayLink_v2.patch";
              hash = "sha256-vWQc2e8a5/YZaaHe+BxfAR/Ni8HOs2sPJ8Nt9pfxqiE=";
            })       
          ];
        });
      })
];
services.xserver.videoDrivers = [ "displaylink" ];
systemd.services.dlm.wantedBy = [ "multi-user.target" ];

Note as of 2024-10-30 nixos-unstable sway uses wlroots_0_18. The patch above applies correctly but you will need to invoke sway with the --unsupported-gpu flag.

Source