From 7517ecd7016cd451fe334718443387242d01642c Mon Sep 17 00:00:00 2001
From: Peter Hoeg <peter@hoeg.com>
Date: Tue, 26 May 2020 21:50:05 +0800
Subject: [PATCH 1/2] powerdevil: add DDC support

---
 pkgs/desktops/plasma-5/powerdevil.nix | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/pkgs/desktops/plasma-5/powerdevil.nix b/pkgs/desktops/plasma-5/powerdevil.nix
index 65fc5446c16..e53e986060f 100644
--- a/pkgs/desktops/plasma-5/powerdevil.nix
+++ b/pkgs/desktops/plasma-5/powerdevil.nix
@@ -3,7 +3,7 @@
   extra-cmake-modules, kdoctools,
   bluez-qt, kactivities, kauth, kconfig, kdbusaddons, kdelibs4support,
   kglobalaccel, ki18n, kidletime, kio, knotifyconfig, kwayland, libkscreen,
-  networkmanager-qt, plasma-workspace, qtx11extras, solid, udev
+  ddcutil, networkmanager-qt, plasma-workspace, qtx11extras, solid, udev
 }:
 
 mkDerivation {
@@ -13,5 +13,9 @@ mkDerivation {
     kconfig kdbusaddons knotifyconfig solid udev bluez-qt kactivities kauth
     kdelibs4support kglobalaccel ki18n kio kidletime kwayland libkscreen
     networkmanager-qt plasma-workspace qtx11extras
+    ddcutil
+  ];
+  cmakeFlags = [
+    "-DHAVE_DDCUTIL=On"
   ];
 }

From a3aec35383b5a4bfd89035b6d2501e03d647772e Mon Sep 17 00:00:00 2001
From: Peter Hoeg <peter@hoeg.com>
Date: Tue, 26 May 2020 22:13:33 +0800
Subject: [PATCH 2/2] nixos/plasma: support setting brightness via DDC

---
 .../services/x11/desktop-managers/plasma5.nix | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/nixos/modules/services/x11/desktop-managers/plasma5.nix b/nixos/modules/services/x11/desktop-managers/plasma5.nix
index 60ef0159ff1..6d48b899d23 100644
--- a/nixos/modules/services/x11/desktop-managers/plasma5.nix
+++ b/nixos/modules/services/x11/desktop-managers/plasma5.nix
@@ -158,6 +158,19 @@ in
         example = "vlc";
         description = "Phonon audio backend to install.";
       };
+
+      supportDDC = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Support setting monitor brightness via DDC.
+          </para>
+          <para>
+          This is not needed for controlling brightness of the internal monitor
+          of a laptop and as it is considered experimental by upstream, it is
+          disabled by default.
+        '';
+      };
     };
 
   };
@@ -184,6 +197,12 @@ in
         };
       };
 
+      # DDC support
+      boot.kernelModules = lib.optional cfg.supportDDC "i2c_dev";
+      services.udev.extraRules = lib.optionalString cfg.supportDDC ''
+        KERNEL=="i2c-[0-9]*", TAG+="uaccess"
+      '';
+
       environment.systemPackages = with pkgs; with qt5; with libsForQt5; with plasma5; with kdeApplications;
         [
           frameworkintegration