feat(brightness): add explicit backlight device override per monitor

example.toml

@@ -211,6 +211,7 @@ enable_ddcutil = false
 # Per-monitor backend override:
 # [brightness.monitor.eDP-1]
 # backend = "backlight"             # auto | none | backlight | ddcutil
+# backlight_device = "intel_backlight"  # explicit sysfs device name or path; run: noctalia msg brightness-list-backlight-devices
 # [brightness.monitor.DP-1]
 # backend = "ddcutil"
 

src/config/config_types.h

@@ -1081,6 +1081,7 @@ constexpr EnumOption<BrightnessBackendPreference> kBrightnessBackendPreferences[
 struct BrightnessMonitorOverride {
   std::string match;
   std::optional<BrightnessBackendPreference> backend;
+  std::optional<std::string> backlightDevice; // sysfs device name or path, e.g. "intel_backlight"
 
   bool operator==(const BrightnessMonitorOverride&) const = default;
 };

src/config/schema/config_schema.cpp

@@ -432,6 +432,19 @@ namespace noctalia::config::schema {
       static const Schema<BrightnessMonitorOverride> s = {
           field(&BrightnessMonitorOverride::match, "match"),
           optionalEnumField(&BrightnessMonitorOverride::backend, "backend", kBrightnessBackendPreferences),
+          custom<BrightnessMonitorOverride>(
+              "backlight_device",
+              [](const toml::table& tbl, BrightnessMonitorOverride& out, std::string_view, Diagnostics&) {
+                if (auto v = tbl["backlight_device"].value<std::string>()) {
+                  out.backlightDevice = *v;
+                }
+              },
+              [](toml::table& tbl, const BrightnessMonitorOverride& in) {
+                if (in.backlightDevice.has_value()) {
+                  tbl.insert_or_assign("backlight_device", *in.backlightDevice);
+                }
+              }
+          ),
       };
       return s;
     }

src/system/brightness_service.cpp

@@ -189,6 +189,34 @@ namespace {
     return BrightnessBackendPreference::Auto;
   }
 
+  // Returns the explicit backlight device name/path configured for this output, if any.
+  std::optional<std::string> backlightDeviceForOutput(const BrightnessConfig& config, const WaylandOutput* output) {
+    if (output == nullptr) {
+      return std::nullopt;
+    }
+
+    for (const auto& override : config.monitorOverrides) {
+      if (override.match.empty() || !outputMatchesSelector(override.match, *output)) {
+        continue;
+      }
+      if (override.backlightDevice.has_value()) {
+        return *override.backlightDevice;
+      }
+      break;
+    }
+
+    return std::nullopt;
+  }
+
+  // Returns the sysfs device name from either a bare name ("intel_backlight") or a path.
+  std::string_view extractBacklightDeviceName(std::string_view deviceSpec) {
+    const auto lastSlash = deviceSpec.rfind('/');
+    if (lastSlash != std::string_view::npos) {
+      return deviceSpec.substr(lastSlash + 1);
+    }
+    return deviceSpec;
+  }
+
   void applyOutputMetadata(BrightnessDisplay& display, const WaylandOutput& output) {
     display.label = output.description.empty() ? output.connectorName : output.description;
     display.physicalWidth = output.width;
@@ -841,6 +869,16 @@ struct BrightnessService::Impl {
         continue;
       }
 
+      if (const auto explicitDevice = backlightDeviceForOutput(activeConfig, output); explicitDevice.has_value()) {
+        if (extractBacklightDeviceName(*explicitDevice) != name) {
+          kLog.debug(
+              "skipping backlight '{}' for connector {} (explicit device '{}' configured)", name, connectorName,
+              *explicitDevice
+          );
+          continue;
+        }
+      }
+
       if (sessionProxy == nullptr) {
         kLog.debug("skipping backlight '{}' because logind brightness control is unavailable", name);
         continue;
@@ -1607,6 +1645,28 @@ void BrightnessService::registerIpc(IpcService& ipc, std::function<void()> onBat
       "brightness-down", -1.0f, "brightness-down [current|*|all|monitor-selector] [step]",
       "Decrease brightness (defaults to current monitor)"
   );
+
+  ipc.registerHandler(
+      "brightness-list-backlight-devices",
+      [](const std::string& /*args*/) -> std::string {
+        const std::string backlightDir = "/sys/class/backlight";
+        DIR* dir = ::opendir(backlightDir.c_str());
+        if (dir == nullptr) {
+          return "error: no backlight devices available\n";
+        }
+        std::string result;
+        while (auto* entry = ::readdir(dir)) {
+          const std::string name = entry->d_name;
+          if (name == "." || name == "..") {
+            continue;
+          }
+          result += name + "\n";
+        }
+        ::closedir(dir);
+        return result.empty() ? "error: no backlight devices available\n" : result;
+      },
+      "brightness-list-backlight-devices", "List available sysfs backlight device names"
+  );
 }
 
 void BrightnessService::setChangeCallback(ChangeCallback callback) { m_impl->changeCallback = std::move(callback); }