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.

Xserver

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
'';

Wayland

At first add displayLink driver to nix store as above described.

evdi module

You probably will need the `evdi` module

boot = {
  extraModulePackages = [ config.boot.kernelPackages.evdi ];
  initrd = {
    # List of modules that are always loaded by the initrd.
    kernelModules = [
      "evdi"
    ];
  };
};

Gnome Wayland

Install displayLink package

environment.systemPackages = with pkgs; [
  displaylink
];

Define videoDrivers

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

Add dlm service

systemd.services.dlm.wantedBy = [ "multi-user.target" ];

KDE Plasma

Apparently KDE Plasma (Wayland) requires a slight different approach.

Esnure you properly enabled wayland session

environment.variables = {
  KWIN_DRM_PREFER_COLOR_DEPTH = "24";
};

services = {
  desktopManager.plasma6 = {
    enable = true;
  };
  displayManager = {
    sddm = {
      enable = true;
      wayland.enable = true;
    };
    defaultSession = "plasma";
  };

};

Install displayLink package

environment.systemPackages = with pkgs; [
  displaylink
];

Instead of dlm setup display-link server as follows:

# --- THIS IS THE CRUCIAL PART FOR ENABLING THE SERVICE ---
systemd.services.displaylink-server = {
  enable = true;
  # Ensure it starts after udev has done its work
  requires = [ "systemd-udevd.service" ];
  after = [ "systemd-udevd.service" ];
  wantedBy = [ "multi-user.target" ]; # Start at boot
  # *** THIS IS THE CRITICAL 'serviceConfig' BLOCK ***
  serviceConfig = {
    Type = "simple"; # Or "forking" if it forks (simple is common for daemons)
    # The ExecStart path points to the DisplayLinkManager binary provided by the package
    ExecStart = "${pkgs.displaylink}/bin/DisplayLinkManager";
    # User and Group to run the service as (root is common for this type of daemon)
    User = "root";
    Group = "root";
    # Environment variables that the service itself might need
    # Environment = [ "DISPLAY=:0" ]; # Might be needed in some cases, but generally not for this
    Restart = "on-failure";
    RestartSec = 5; # Wait 5 seconds before restarting
  };
};

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