[WIP RFC v2 23/35] rust: drm/kms: Add DriverPlane::atomic_check()

[Lyude Paul]

Optional trait method for implementing a plane's atomic_check().

Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 rust/kernel/drm/kms/plane.rs | 41 +++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
index 506ed5ced1270..04f1bdfbb1ea2 100644
--- a/rust/kernel/drm/kms/plane.rs
+++ b/rust/kernel/drm/kms/plane.rs
@@ -74,7 +74,7 @@ pub trait DriverPlane: Send + Sync + Sized {
             cleanup_fb: None,
             begin_fb_access: None, // TODO: someday?
             end_fb_access: None, // TODO: someday?
-            atomic_check: None,
+            atomic_check: if Self::HAS_ATOMIC_CHECK { Some(atomic_check_callback::<Self>) } else { None },
             atomic_update: if Self::HAS_ATOMIC_UPDATE { Some(atomic_update_callback::<Self>) } else { None },
             atomic_enable: None, // TODO
             atomic_disable: None, // TODO
@@ -118,6 +118,21 @@ fn atomic_update(
     ) {
         build_error::build_error("This should not be reachable")
     }
+
+    /// The optional [`drm_plane_helper_funcs.atomic_check`] hook for this plane.
+    ///
+    /// Drivers may use this to customize the atomic check phase of their [`Plane`] objects. The
+    /// result of this function determines whether the atomic check passed or failed.
+    ///
+    /// [`drm_plane_helper_funcs.atomic_check`]: srctree/include/drm/drm_modeset_helper_vtables.h
+    fn atomic_check(
+        plane: &Plane<Self>,
+        new_state: BorrowedPlaneState<'_, PlaneState<Self::State>>,
+        old_state: &PlaneState<Self::State>,
+        state: &AtomicStateComposer<Self::Driver>
+    ) -> Result {
+        build_error::build_error("This should not be reachable")
+    }
 }
 
 /// The generated C vtable for a [`DriverPlane`].
@@ -794,3 +809,27 @@ fn deref_mut(&mut self) -> &mut Self::Target {
 
     T::atomic_update(plane, new_state, old_state, &state);
 }
+
+unsafe extern "C" fn atomic_check_callback<T: DriverPlane>(
+    plane: *mut bindings::drm_plane,
+    state: *mut bindings::drm_atomic_state,
+) -> i32 {
+    // SAFETY:
+    // * We're guaranteed `plane` is of type `Plane<T>` via type invariants.
+    // * We're guaranteed by DRM that `plane` is pointing to a valid initialized state.
+    let plane = unsafe { Plane::from_raw(plane) };
+
+    // SAFETY: We're guaranteed by DRM that `state` points to a valid instance of `drm_atomic_state`
+    let state = ManuallyDrop::new(unsafe {
+        AtomicStateComposer::<T::Driver>::new(NonNull::new_unchecked(state))
+    });
+
+    // SAFETY: We're guaranteed by DRM that both the old and new atomic state are present within
+    // this `drm_atomic_state`
+    let (old_state, new_state) = unsafe {(
+        state.get_old_plane_state(plane).unwrap_unchecked(),
+        state.get_new_plane_state(plane).unwrap_unchecked(),
+    )};
+
+    from_result(|| T::atomic_check(plane, new_state, old_state, &state).map(|_| 0))
+}
-- 
2.46.1