[PATCH v3 13/23] rust: drm: kms: plane: add FB_DAMAGE_CLIPS property support

Userspace can only hand a driver the rectangles that actually changed
between two framebuffers if the plane advertises the FB_DAMAGE_CLIPS
property. Without it a compositor supplies nothing, and unchanged
commits are indistinguishable from missing damage information --
which forces a driver either to freeze or to re-send whole frames.

That matters most for drivers uploading their scanout over a slow link.
Wrap `drm_plane_enable_fb_damage_clips()` so a plane can attach
the property before registration, alongside the existing rotation
property helper.

The consumer is the vino DisplayLink driver, which encodes and sends
only the changed strips of each frame over USB.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Mike Lothian <[email protected]>
---
 rust/kernel/drm/kms/plane.rs | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
index bc830503b142..62de8a1dad19 100644
--- a/rust/kernel/drm/kms/plane.rs
+++ b/rust/kernel/drm/kms/plane.rs
@@ -438,6 +438,27 @@ pub fn create_rotation_property(
             )
         })
     }
+
+    /// Attaches the `FB_DAMAGE_CLIPS` property to this plane.
+    ///
+    /// Userspace can then hand the driver the list of rectangles that actually changed between two
+    /// framebuffers, instead of leaving it to infer damage from a buffer swap. Drivers that upload
+    /// their scanout over a slow link -- USB display adapters especially -- need this to send only
+    /// the changed regions.
+    ///
+    /// Without the property attached, a compositor cannot supply clips at all: unchanged commits
+    /// arrive with an empty list, which is indistinguishable from "no damage information".
+    ///
+    /// The clips are read back through
+    /// [`RawPlaneState::damage_clips`](crate::drm::kms::plane::RawPlaneState::damage_clips).
+    ///
+    /// Call this during [`KmsDriver::create_objects`](crate::drm::kms::KmsDriver::create_objects),
+    /// before the device is registered.
+    pub fn enable_fb_damage_clips(&self) {
+        // SAFETY: `as_raw()` is a valid, not-yet-registered plane; attaching a property before
+        // registration is exactly what this helper is for.
+        unsafe { bindings::drm_plane_enable_fb_damage_clips(self.as_raw()) }
+    }
 }
 
 /// A trait implemented by any type that acts as a [`struct drm_plane`] interface.