WIP: rust/kms/drm: Add RawPlaneState::atomic_helper_check()

Add a binding for DRM's plane state atomic check helper.

TODO:
* Finish up documentation (we need to document parameters too! I think?)

Signed-off-by: Lyude Paul <lyude@redhat.com>

rust/kernel/drm/kms/plane.rs

@@ -396,6 +396,31 @@ pub trait RawPlaneState: AsRawPlaneState {
         // SAFETY: We're guaranteed `crtc` is of type `OpaqueCrtc` by type invariance
         NonNull::new(self.as_raw().crtc).map(|c| unsafe { OpaqueCrtc::from_raw(c.as_ptr()) })
     }
+
+    /// Run the atomic check helper for this plane and the given CRTC state
+    fn atomic_helper_check<S>(
+        &mut self,
+        crtc_state: &BorrowedCrtcState<'_, S>,
+        can_position: bool,
+        can_update_disabled: bool
+    ) -> Result
+    where
+        S: FromRawCrtcState,
+        S::Crtc: AsRawCrtc<Driver = <Self::Plane as ModeObject>::Driver>
+    {
+        // SAFETY: We're passing the mutable reference from `self.as_raw_mut()` directly to DRM,
+        // which is safe.
+        to_result(unsafe {
+            bindings::drm_atomic_helper_check_plane_state(
+                self.as_raw_mut(),
+                crtc_state.as_raw(),
+                bindings::DRM_PLANE_NO_SCALING as _, // TODO: add parameters for scaling
+                bindings::DRM_PLANE_NO_SCALING as _,
+                can_position,
+                can_update_disabled
+            )
+        })
+    }
 }
 impl<T: AsRawPlaneState + ?Sized> RawPlaneState for T {}