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"
    ];
  };
};
<syntaxhighlight lang="nix">

====='''Gnome Wayland'''=====

Install displayLink package

{{bc|<nowiki>
environment.systemPackages = with pkgs; [
  displaylink
];
</nowiki>}}

Define videoDrivers
{{bc|<nowiki>
services.xserver.videoDrivers = [ "displaylink" ];
</nowiki>}}

Add dlm service
{{bc|<nowiki>
systemd.services.dlm.wantedBy = [ "multi-user.target" ];
</nowiki>}}
====='''KDE Plasma'''=====

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

Esnure you properly enabled wayland session 

{{bc|<nowiki>
environment.variables = {
  KWIN_DRM_PREFER_COLOR_DEPTH = "24";
};

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

};
</nowiki>}}

Install displayLink package

{{bc|<nowiki>
environment.systemPackages = with pkgs; [
  displaylink
];
</nowiki>}}

Instead of dlm setup display-link server as follows:

{{bc|<nowiki>
# --- 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
  };
};
</nowiki>}}

==Sway==
Identify which card has the render device, <code>evdi</code> is the DisplayLink interface, so it's not <code>card0</code>, but <code>card1</code>.

<syntaxhighlight lang="console">
$ 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

Troubleshooting

Suspend blocked by `pre-sleep.service`

As of NixOS 25.05, installing pkgs.displaylink inserts some directives into the script referenced by pre-sleep.service. If suspending does not work and causes the reboot and poweroff buttons to stop working, it may be a symptom of suspend being blocked by pre-sleep.service.

The script in question:

#!/nix/store/cfqbabpc7xwg8akbcchqbq3cai6qq2vs-bash-5.2p37/bin/bash
set -e

#flush any bytes in pipe
while read -n 1 -t 1 SUSPEND_RESULT < /tmp/PmMessagesPort_out; do : ; done;

#suspend DisplayLinkManager
echo "S" > /tmp/PmMessagesPort_in

#wait until suspend of DisplayLinkManager finish
if [ -f /tmp/PmMessagesPort_out ]; then
  #wait until suspend of DisplayLinkManager finish
  read -n 1 -t 10 SUSPEND_RESULT < /tmp/PmMessagesPort_out
fi

Because of a stray /tmp/PmMessagesPort_out caused by an unclean shutdown, the suspend action was blocked by this script trying to flush the port. A myriad of solutions can be used to unblock the script and restore suspend:

Start dlm.service so that DisplayLinkManager can clear the ports and unblock the script
Use sudo DisplayLinkManager to clear the ports and unblock the script

Untested solutions:

Removing the file
Killing the script