Disable ahmed's screen

2 files changed, 52 insertions, 12 deletions

diff --git a/hosts/ahmed/configuration.nix b/hosts/ahmed/configuration.nix
index 8a93021..3afe509 100644
--- a/hosts/ahmed/configuration.nix
+++ b/hosts/ahmed/configuration.nix
@@ -8,6 +8,7 @@
     [
       ./hardware-configuration.nix
       ./ssh.nix
+      ./disable-screen.nix
     ];
 
   # Create the main user.
@@ -35,18 +36,6 @@
     keyMap = "dk";     # This host has a Danish keyboard layout.
   };
 
-  # Disable sleep on lid close.
-  # FIXME: Screen does not appear to turn off when closed.
-  services.logind =
-    let
-      lidSwitchAction = "ignore";
-    in
-    {
-      lidSwitchExternalPower = lidSwitchAction;
-      lidSwitchDocked = lidSwitchAction;
-      lidSwitch = lidSwitchAction;
-    };
-
   # Configure WiFi at computer's location.
   # FIXME: Don't store in plain text.
   networking.wireless.enable = true;
diff --git a/hosts/ahmed/disable-screen.nix b/hosts/ahmed/disable-screen.nix
new file mode 100644
index 0000000..dd5eb22
--- /dev/null
+++ b/hosts/ahmed/disable-screen.nix
@@ -0,0 +1,51 @@
+# This file defines some configuration options which disable the screen. This
+# is only relevant because this host is an old laptop running as a server.
+
+{ pkgs, config, lib, ... }:
+
+let
+  # The path to the device.
+  device-path = "/sys/class/backlight/intel_backlight";
+
+  # The systemd device unit which corresponds to `device-path`.
+  device-unit = "sys-devices-pci0000:00-0000:00:02.0-drm-card0-card0\\x2deDP\\x2d1-intel_backlight.device";
+in
+{
+  # Disable sleep on lid close.
+  services.logind =
+    let
+      lidSwitchAction = "ignore";
+    in
+    {
+      lidSwitchExternalPower = lidSwitchAction;
+      lidSwitchDocked = lidSwitchAction;
+      lidSwitch = lidSwitchAction;
+    };
+
+  # Don't store screen brightness between boots. We always want to turn off the
+  # screen.
+  #
+  # See: https://wiki.archlinux.org/title/backlight#Save_and_restore_functionality
+  # See: https://github.com/NixOS/nixpkgs/blob/990398921f677615c0732d704857484b84c6c888/nixos/modules/system/boot/systemd.nix#L97-L101
+  systemd.suppressedSystemUnits = [ "[email protected]" ];
+
+  # FIXME: Figure out how to enable screen when on-device debugging is necessary.
+  # Create a new service which turns off the display on boot.
+  #
+  # See: https://nixos.wiki/wiki/Backlight#.2Fsys.2Fclass.2Fbacklight.2F...
+  # See: https://superuser.com/questions/851846/how-to-write-a-systemd-service-that-depends-on-a-device-being-present
+  systemd.services.disable-screen =
+    {
+      requires = [ device-unit ];
+      after = [ device-unit ];
+      wantedBy = [ device-unit ];
+
+      serviceConfig.Type = "oneshot";
+      script = ''
+        tee ${device-path}/brightness <<<0
+      '';
+    };
+
+  warnings = lib.optional config.my.modules.graphics.enable
+    "You have enabled a graphical environment but the screen is still being disabled";
+}