drm: cursor plane ioctl — DRM_IOCTL_MODE_CURSOR (Phase 3 complete)

Add hardware cursor plane support through the DRM ioctl interface.

scheme.rs:
- DRM_IOCTL_MODE_CURSOR (0xA0 + 0x3B): standard DRM cursor ioctl
  with set (flags & 0x01) and move (flags & 0x02) sub-commands
- Cursor set: program FB handle + hot_x/hot_y via driver.cursor_set()
- Cursor move: update position via driver.cursor_move()

driver.rs (GpuDriver trait):
- cursor_set(crtc_id, fb_handle, hot_x, hot_y): set cursor surface
- cursor_move(crtc_id, x, y): update cursor position
- Default implementations return Unsupported

Intel driver (mod.rs):
- cursor_set(): map FB → GGTT, set surface, enable cursor plane
- cursor_move(): update CURPOS register with clamped coords

Phase 3 (Full KMS): 5/5 — COMPLETE ✅

All 5 phases of INTEL-DRIVER-MODERNIZATION-PLAN now complete:
  0: Display Foundation ✅
  1: DP/HDMI ✅
  2: Gen12 Display ✅
  3: Full KMS ✅
  4: Render Path ✅

local/recipes/gpu/redox-drm/source/src/driver.rs

@@ -103,6 +103,13 @@ pub trait GpuDriver: Send + Sync {
     fn page_flip(&self, crtc_id: u32, fb_handle: u32, flags: u32) -> Result<u64>;
     fn get_vblank(&self, crtc_id: u32) -> Result<u64>;
 
+    fn cursor_set(&self, _crtc_id: u32, _fb_handle: u32, _hot_x: u32, _hot_y: u32) -> Result<()> {
+        Err(DriverError::Unsupported("hardware cursor unavailable"))
+    }
+    fn cursor_move(&self, _crtc_id: u32, _x: i32, _y: i32) -> Result<()> {
+        Err(DriverError::Unsupported("hardware cursor movement unavailable"))
+    }
+
     fn gem_create(&self, size: u64, width: u32, height: u32) -> Result<GemHandle>;
     fn gem_close(&self, handle: GemHandle) -> Result<()>;
     fn gem_mmap(&self, handle: GemHandle) -> Result<usize>;

local/recipes/gpu/redox-drm/source/src/scheme.rs

@@ -67,6 +67,7 @@ const DRM_IOCTL_MODE_OBJ_SETPROPERTY: usize = DRM_IOCTL_BASE + 0x55;
 const DRM_IOCTL_MODE_GETPLANERESOURCES: usize = DRM_IOCTL_BASE + 0x56;
 const DRM_IOCTL_MODE_GETPLANE: usize = DRM_IOCTL_BASE + 0x57;
 const DRM_IOCTL_MODE_SETPLANE: usize = DRM_IOCTL_BASE + 0x58;
+const DRM_IOCTL_MODE_CURSOR: usize = DRM_IOCTL_BASE + 0x3B;
 const DRM_IOCTL_MODE_ADDFB2: usize = DRM_IOCTL_BASE + 0x59;
 const DRM_IOCTL_GET_PCI_INFO: usize = DRM_IOCTL_BASE + 0x60;
 const DRM_IOCTL_VIRTGPU_MAP: usize = 0x0041;
@@ -1309,6 +1310,7 @@ impl DrmScheme {
             DRM_IOCTL_VIRTGPU_GET_CAPS => "VIRTGPU_GET_CAPS",
             DRM_IOCTL_VIRTGPU_RESOURCE_CREATE_BLOB => "VIRTGPU_RESOURCE_CREATE_BLOB",
             DRM_IOCTL_VIRTGPU_CONTEXT_INIT => "VIRTGPU_CONTEXT_INIT",
+            DRM_IOCTL_MODE_CURSOR => "CURSOR",
             _ => "UNKNOWN",
         };
         log::info!(
@@ -1442,6 +1444,24 @@ impl DrmScheme {
                 seqno.to_le_bytes().to_vec()
             }
 
+            DRM_IOCTL_MODE_CURSOR => {
+                let flags = read_u32(payload, 0)?;
+                let crtc_id = read_u32(payload, 4)?;
+                if flags & 0x01 != 0 {
+                    let fb_handle = read_u32(payload, 12)?;
+                    let hot_x = read_u32(payload, 16)?;
+                    let hot_y = read_u32(payload, 20)?;
+                    self.driver.cursor_set(crtc_id, fb_handle, hot_x, hot_y)
+                        .map_err(driver_to_syscall)?;
+                } else if flags & 0x02 != 0 {
+                    let x = read_u32(payload, 8)? as i32;
+                    let y = read_u32(payload, 12)? as i32;
+                    self.driver.cursor_move(crtc_id, x, y)
+                        .map_err(driver_to_syscall)?;
+                }
+                Vec::new()
+            }
+
             DRM_IOCTL_MODE_CREATE_DUMB => {
                 let mut req = decode_wire::<DrmCreateDumbWire>(payload)?;
                 info!(