Add egpu nix configuration from laptop

etc/nixos/egpu.nix

@@ -0,0 +1,45 @@
+{ config, pkgs, lib, ... }:
+
+let
+  keyValues = (key: values: lib.strings.concatStringsSep " " [
+    key
+    (lib.strings.concatMapStringsSep " " (value: lib.strings.concatStrings [ "\"" value "\"" ]) values)
+  ]);
+
+  keyValue = (key: value: keyValues key [ value ]);
+
+  section = (name: strings: lib.strings.concatStrings [
+    (keyValue "Section" name)
+    (lib.strings.concatStringsSep "\n  " strings)
+    "EndSection"
+  ]);
+
+  nvidia = ({ side, busID }: {
+    system.nixos.tags = [ "eGPU" side ];
+
+    # boot.kernelPackages = lib.mkForce pkgs.linuxPackages;
+
+    # Set X11 to use Nvidia drivers
+    services.xserver.videoDrivers = [ "nvidia" ];
+
+    hardware.opengl.enable = true;
+    hardware.nvidia.package = config.boot.kernelPackages.nvidiaPackages.stable;
+    services.xserver.config = pkgs.lib.mkOverride 0 (lib.strings.concatStringsSep "\n\n" [
+      (section "Module" [ (keyValue "Load" "modesetting") ])
+      (section "Device" [
+        (keyValue "Identifier" "Device0")
+        (keyValue "Driver" "nvidia")
+        (keyValue "BusID" busID)
+        (keyValue "Option" "AllowEmptyInitialConfiguration")
+        (keyValues "Option" [ "AllowExternalGpus" "True" ])
+      ])
+    ]);
+  });
+in {
+  # eGPU specialisation config 
+  specialisation = {
+    eGPUright.configuration = nvidia { side = "right"; busID = "4:0:0"; };
+
+    eGPUleft.configuration = nvidia { side = "left"; busID = "2:0:0"; };
+  };
+}