[idd] input: report volume keys as consumer controls

Expose a Consumer Control HID report for the system volume usages that
Windows does not handle through the Keyboard/Keypad usage page.

Translate the existing mute and volume keyboard usages at the LGInput
boundary, preserve normal keyboard state, and force a neutral consumer
report across resets and HID device reactivation.

idd/LGInput/CHIDDevice.cpp

@@ -59,6 +59,7 @@ struct HIDDeviceContext
   size_t                reportCount;
   uint32_t              relativeButtons;
   uint32_t              absoluteButtons;
+  uint16_t              consumerUsage;
   bool                  absoluteValid;
   uint16_t              absoluteX;
   uint16_t              absoluteY;
@@ -329,6 +330,7 @@ static NTSTATUS DeactivateDevice(_Inout_ HIDDeviceContext * context)
     context->active        = false;
     context->reportHead    = 0;
     context->reportCount   = 0;
+    context->consumerUsage = UINT16_MAX;
   }
   WdfIoQueuePurgeSynchronously(context->reportQueue);
   return STATUS_SUCCESS;
@@ -449,6 +451,11 @@ NTSTATUS CHIDDevice::SubmitReport(
       status = STATUS_DEVICE_NOT_READY;
     else
     {
+      if (reportId == HID_REPORT_ID_CONSUMER &&
+          context->consumerUsage ==
+            static_cast<const HIDConsumerReport *>(report)->usage)
+        return STATUS_SUCCESS;
+
       bool pureMotion = false;
       switch (reportId)
       {
@@ -510,6 +517,11 @@ NTSTATUS CHIDDevice::SubmitReport(
             break;
           }
 
+          case HID_REPORT_ID_CONSUMER:
+            context->consumerUsage =
+              static_cast<const HIDConsumerReport *>(report)->usage;
+            break;
+
           default:
             break;
         }
@@ -546,6 +558,7 @@ NTSTATUS CHIDDevice::ResetReports()
     context->mouseMode         = 0;
     context->relativeButtons   = 0;
     context->absoluteButtons   = 0;
+    context->consumerUsage     = UINT16_MAX;
   }
 
   const HIDMouseRelativeReport relative = {
@@ -558,6 +571,9 @@ NTSTATUS CHIDDevice::ResetReports()
   const HIDKeyboardReport keyboard = {
     HID_REPORT_ID_KEYBOARD,
   };
+  const HIDConsumerReport consumer = {
+    HID_REPORT_ID_CONSUMER,
+  };
 
   NTSTATUS status = SubmitReport(&relative, sizeof(relative));
   if (absoluteValid)
@@ -578,6 +594,10 @@ NTSTATUS CHIDDevice::ResetReports()
     SubmitReport(&keyboard, sizeof(keyboard));
   if (NT_SUCCESS(status))
     status = keyboardStatus;
+  const NTSTATUS consumerStatus =
+    SubmitReport(&consumer, sizeof(consumer));
+  if (NT_SUCCESS(status))
+    status = consumerStatus;
   return status;
 }
 

idd/LGInput/HIDReports.cpp

@@ -120,6 +120,20 @@ static const uint8_t REPORT_DESCRIPTOR[] =
   0x95, 0x06,             // Report Count (6)
   0x81, 0x00,             // Input (Data, Array, Absolute)
   0xC0,                   // End Collection
+
+  // Consumer control, report ID 4.
+  0x05, 0x0C,             // Usage Page (Consumer)
+  0x09, 0x01,             // Usage (Consumer Control)
+  0xA1, 0x01,             // Collection (Application)
+  0x85, HID_REPORT_ID_CONSUMER,
+  0x19, 0x00,             // Usage Minimum (Unassigned)
+  0x2A, 0xFF, 0x03,       // Usage Maximum (1023)
+  0x15, 0x00,             // Logical Minimum (0)
+  0x26, 0xFF, 0x03,       // Logical Maximum (1023)
+  0x75, 0x10,             // Report Size (16)
+  0x95, 0x01,             // Report Count (1)
+  0x81, 0x00,             // Input (Data, Array, Absolute)
+  0xC0,                   // End Collection
 };
 
 const uint8_t * HIDGetReportDescriptor()
@@ -145,6 +159,9 @@ size_t HIDGetInputReportSize(uint8_t reportId)
     case HID_REPORT_ID_KEYBOARD:
       return sizeof(HIDKeyboardReport);
 
+    case HID_REPORT_ID_CONSUMER:
+      return sizeof(HIDConsumerReport);
+
     default:
       return 0;
   }

idd/LGInput/HIDReports.h

@@ -28,6 +28,7 @@ enum HIDReportId : uint8_t
   HID_REPORT_ID_MOUSE_ABSOLUTE = 1,
   HID_REPORT_ID_MOUSE_RELATIVE = 2,
   HID_REPORT_ID_KEYBOARD       = 3,
+  HID_REPORT_ID_CONSUMER       = 4,
 };
 
 #pragma pack(push, 1)
@@ -64,12 +65,19 @@ struct HIDKeyboardLedsReport
   uint8_t leds;
 };
 
+struct HIDConsumerReport
+{
+  uint8_t  reportId;
+  uint16_t usage;
+};
+
 #pragma pack(pop)
 
 static_assert(sizeof(HIDMouseAbsoluteReport) == 10);
 static_assert(sizeof(HIDMouseRelativeReport) == 10);
 static_assert(sizeof(HIDKeyboardReport)     == 9);
 static_assert(sizeof(HIDKeyboardLedsReport) == 2);
+static_assert(sizeof(HIDConsumerReport)     == 3);
 
 static constexpr size_t HID_MAX_INPUT_REPORT_SIZE =
   sizeof(HIDMouseAbsoluteReport);

idd/LGInput/ipc/CInputPipeClient.cpp

@@ -27,6 +27,14 @@
 
 #include <string.h>
 
+static constexpr uint8_t HID_KEYBOARD_USAGE_MUTE        = 0x7f;
+static constexpr uint8_t HID_KEYBOARD_USAGE_VOLUME_UP   = 0x80;
+static constexpr uint8_t HID_KEYBOARD_USAGE_VOLUME_DOWN = 0x81;
+
+static constexpr uint16_t HID_CONSUMER_USAGE_MUTE        = 0xe2;
+static constexpr uint16_t HID_CONSUMER_USAGE_VOLUME_UP   = 0xe9;
+static constexpr uint16_t HID_CONSUMER_USAGE_VOLUME_DOWN = 0xea;
+
 bool CInputPipeClient::Start()
 {
   m_lastSequence = 0;
@@ -209,14 +217,45 @@ bool CInputPipeClient::HandleKeyboard(
   HIDKeyboardReport report = {};
   report.reportId = HID_REPORT_ID_KEYBOARD;
   report.modifiers = input.modifiers;
+  // The Consumer Control report carries one active array usage.
+  uint16_t consumerUsage = 0;
+  size_t   keyIndex      = 0;
   for (size_t i = 0; i < LG_INPUT_KEYBOARD_KEY_COUNT; ++i)
   {
     if (input.keys[i] > LG_INPUT_KEYBOARD_USAGE_MAX)
       return false;
-    report.keys[i] = input.keys[i];
+
+    switch (input.keys[i])
+    {
+      case HID_KEYBOARD_USAGE_MUTE:
+        if (!consumerUsage)
+          consumerUsage = HID_CONSUMER_USAGE_MUTE;
+        break;
+
+      case HID_KEYBOARD_USAGE_VOLUME_UP:
+        if (!consumerUsage)
+          consumerUsage = HID_CONSUMER_USAGE_VOLUME_UP;
+        break;
+
+      case HID_KEYBOARD_USAGE_VOLUME_DOWN:
+        if (!consumerUsage)
+          consumerUsage = HID_CONSUMER_USAGE_VOLUME_DOWN;
+        break;
+
+      default:
+        report.keys[keyIndex++] = input.keys[i];
+        break;
+    }
   }
 
-  return SubmitReport(&report, sizeof(report));
+  if (!SubmitReport(&report, sizeof(report)))
+    return false;
+
+  const HIDConsumerReport consumer = {
+    HID_REPORT_ID_CONSUMER,
+    consumerUsage,
+  };
+  return SubmitReport(&consumer, sizeof(consumer));
 }
 
 bool CInputPipeClient::SubmitReport(