nixos/ddccontrol: enable hardware.i2c and mention its group

doc/release-notes/rl-2511.section.md

@@ -96,6 +96,8 @@
 
 - `spidermonkey_91` has been removed, as it has been EOL since September 2022.
 
+- `ddccontrol` service now enables `hardware.i2c` by default, and adds `ddcci_backlight` to the kernel modules, based on [experiences reported on discourse](https://discourse.nixos.org/t/brightness-control-of-external-monitors-with-ddcci-backlight/8639/).
+
 - The license of duckstation has changed from `gpl3Only` to `cc-by-nc-nd-40` making it unfree in newer releases. The `duckstation` package has been overhauled to support the new releases and `duckstation-bin` has been aliased to `duckstation` to support darwin binary builds.
 
 - `hiawata` has been removed, due to lack of active development upstream, lack of maintainership downstream and upcoming security issues.

nixos/modules/services/hardware/ddccontrol.nix

@@ -14,15 +14,25 @@ in
 
   options = {
     services.ddccontrol = {
-      enable = lib.mkEnableOption "ddccontrol for controlling displays";
+      enable = lib.mkEnableOption ''
+        ddccontrol for controlling displays.
+
+        This [enables `hardware.i2c`](#opt-hardware.i2c.enable), so note to add
+        yourself to [`hardware.i2c.group`](#opt-hardware.i2c.group).
+      '';
     };
   };
 
   ###### implementation
 
   config = lib.mkIf cfg.enable {
+    boot.kernelModules = [
+      "ddcci_backlight"
+    ];
     # Load the i2c-dev module
-    boot.kernelModules = [ "i2c_dev" ];
+    hardware.i2c = {
+      enable = true;
+    };
 
     # Give users access to the "gddccontrol" tool
     environment.systemPackages = [