Use systemd unit to create AMD uprof device

m/module/amd-uprof.nix

@@ -17,23 +17,33 @@
     # First make sure that we add the module to the list of available modules
     # in the kernel matching the same kernel version of this configuration.
     boot.extraModulePackages = with config.boot.kernelPackages; [ amd-uprof-driver ];
+    boot.kernelModules = [ "AMDPowerProfiler" ];
 
     # Make the userspace tools available in $PATH.
     environment.systemPackages = with pkgs; [ amd-uprof ];
 
-    # Add extra udev rules to setup the /dev/AMDPowerProfiler device. They
-    # forgot to add these.
-    services.udev.extraRules = let
-      # To create the device node we need to read the device number from the
-      # /proc directory, so the module must have been loaded first.
-      addDevice = pkgs.writeScript "add-amd-uprof-dev.sh"
-        "mknod /dev/AMDPowerProfiler -m 666 c $(< /proc/AMDPowerProfiler/device) 0";
-      removeDevice = pkgs.writeScript "remove-amd-uprof-dev.sh"
-        "rm /dev/AMDPowerProfiler";
-    in
-      ''
-        SUBSYSTEM=="module", DEVPATH=="/module/AMDPowerProfiler/device", ACTION=="add", RUN+="${addDevice}"
-        SUBSYSTEM=="module", DEVPATH=="/module/AMDPowerProfiler/device", ACTION=="remove", RUN+="${removeDevice}"
-      '';
+    # The AMDPowerProfiler module doesn't create the /dev device nor it emits
+    # any uevents, so we cannot use udev rules to automatically create the
+    # device. Instead, we run a systemd unit that does it after loading the
+    # modules.
+    systemd.services.amd-uprof-device = {
+      description = "Create /dev/AMDPowerProfiler device";
+      after = [ "systemd-modules-load.service" ];
+      wantedBy = [ "multi-user.target" ];
+      unitConfig.ConditionPathExists = [
+          "/proc/AMDPowerProfiler/device"
+          "!/dev/AMDPowerProfiler"
+      ];
+      serviceConfig = {
+        Type = "oneshot";
+        RemainAfterExit = true;
+        ExecStart = pkgs.writeShellScript "add-amd-uprof-dev.sh" ''
+          mknod /dev/AMDPowerProfiler -m 666 c $(< /proc/AMDPowerProfiler/device) 0
+        '';
+        ExecStop = pkgs.writeShellScript "remove-amd-uprof-dev.sh" ''
+          rm -f /dev/AMDPowerProfiler
+        '';
+      };
+    };
   };
 }