fix: add backlight modulation support for hybrid graphics laptops

kernel/src/Api/BuildNo.hpp

@@ -12,4 +12,4 @@
 
 #pragma once
 
-#define MONTAUK_BUILD_NUMBER 287
+#define MONTAUK_BUILD_NUMBER 288

kernel/src/Api/Graphics.hpp

@@ -12,6 +12,7 @@
 #include <Graphics/Framebuffer.hpp>
 #include <Drivers/Graphics/IntelGPU.hpp>
 #include <ACPI/AcpiVideo.hpp>
+#include <ACPI/WmiEcBacklight.hpp>
 #include <Terminal/Terminal.hpp>
 
 #include "Syscall.hpp"
@@ -129,29 +130,38 @@ namespace montauk::abi {
         return GPU::Flip((int)index, (flags & 1) != 0, proc->pid);
     }
 
-    // The firmware's ACPI brightness methods drive the built-in panel, so
-    // they stand in only when that panel is what is on screen (or no native
-    // driver knows what is): never for an external monitor without DDC/CI.
-    static bool AcpiBrightnessApplies() {
+    // Firmware brightness interfaces (EC via WMI, ACPI _BCM) drive the
+    // built-in panel, so they apply only while that panel is what is on
+    // screen (or no native driver knows what is): never for an external
+    // monitor, where they would silently dim a closed lid instead.
+    static bool PanelIsActiveOutput() {
         if (!Drivers::Graphics::IntelGPU::IsInitialized()) return true;
         uint8_t type = Drivers::Graphics::IntelGPU::ActiveConnectorType();
         return type == DISPLAY_CONNECTOR_EDP || type == DISPLAY_CONNECTOR_LVDS;
     }
 
+    // Order follows who actually owns the backlight. A firmware that names
+    // the EC as the source has taken it away from the GPU, whose PWM then
+    // still accepts writes that reach nothing; so the EC interface goes
+    // first, then the GPU's own controls, then ACPI _BCM as a last resort.
     static int DisplayBrightness(int percent) {
+        bool panel = PanelIsActiveOutput();
+        if (panel) {
+            int rc = Hal::WmiEcBacklight::Brightness(percent);
+            if (rc != -1) return rc;
+        }
         int rc = Drivers::Graphics::IntelGPU::Brightness(percent);
-        if (rc == -1 && AcpiBrightnessApplies())
-            rc = Hal::AcpiVideo::Brightness(percent);
+        if (rc == -1 && panel) rc = Hal::AcpiVideo::Brightness(percent);
         return rc;
     }
 
     static int64_t Sys_DisplayInfo(DisplayInfo* out) {
         if (!Drivers::Graphics::IntelGPU::GetDisplayInfo(out)) return NoDevice;
-        if (out->brightness < 0 && AcpiBrightnessApplies()) {
-            out->brightness = Hal::AcpiVideo::Brightness(-1);
-            if (out->brightness >= 0) out->capabilities |= DISPLAY_CAP_BRIGHTNESS;
-            else out->brightness = -1;
-        }
+        // The driver only knows its own backends; report what a set would use.
+        int level = DisplayBrightness(-1);
+        out->brightness = level >= 0 ? level : -1;
+        if (level >= 0) out->capabilities |= DISPLAY_CAP_BRIGHTNESS;
+        else out->capabilities &= ~DISPLAY_CAP_BRIGHTNESS;
         return Success;
     }