[WIP RFC v2 29/35] rust: drm/kms: Add DriverCrtc::atomic_begin() and atomic_flush()

[Lyude Paul]

Optional trait methods for implementing the atomic_begin and atomic_flush
callbacks for a CRTC.

Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 rust/kernel/drm/kms/crtc.rs | 78 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 76 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/drm/kms/crtc.rs b/rust/kernel/drm/kms/crtc.rs
index ec9b58763dcca..a4e955364bd8c 100644
--- a/rust/kernel/drm/kms/crtc.rs
+++ b/rust/kernel/drm/kms/crtc.rs
@@ -90,8 +90,8 @@ pub trait DriverCrtc: Send + Sync + Sized {
             mode_set: None,
             mode_valid: None,
             mode_fixup: None,
-            atomic_begin: None,
-            atomic_flush: None,
+            atomic_begin: if Self::HAS_ATOMIC_BEGIN { Some(atomic_begin_callback::<Self>) } else { None },
+            atomic_flush: if Self::HAS_ATOMIC_FLUSH { Some(atomic_flush_callback::<Self>) } else { None },
             mode_set_nofb: None,
             mode_set_base: None,
             mode_set_base_atomic: None,
@@ -132,6 +132,36 @@ fn atomic_check(
     ) -> Result {
         build_error::build_error("This should not be reachable")
     }
+
+    /// The optional [`drm_crtc_helper_funcs.atomic_begin`] hook.
+    ///
+    /// This hook will be called before a set of [`Plane`] updates are performed for the given
+    /// [`Crtc`].
+    ///
+    /// [`drm_crtc_helper_funcs.atomic_begin`]: srctree/include/drm/drm_modeset_helper_vtables.h
+    fn atomic_begin(
+        crtc: &Crtc<Self>,
+        old_state: &CrtcState<Self::State>,
+        new_state: BorrowedCrtcState<'_, CrtcState<Self::State>>,
+        state: &AtomicStateMutator<Self::Driver>
+    ) {
+        build_error::build_error("This should not be reachable")
+    }
+
+    /// The optional [`drm_crtc_helper_funcs.atomic_flush`] hook.
+    ///
+    /// This hook will be called after a set of [`Plane`] updates are performed for the given
+    /// [`Crtc`].
+    ///
+    /// [`drm_crtc_helper_funcs.atomic_flush`]: srctree/include/drm/drm_modeset_helper_vtables.h
+    fn atomic_flush(
+        crtc: &Crtc<Self>,
+        old_state: &CrtcState<Self::State>,
+        new_state: BorrowedCrtcState<'_, CrtcState<Self::State>>,
+        state: &AtomicStateMutator<Self::Driver>
+    ) {
+        build_error::build_error("This should never be reachable")
+    }
 }
 
 /// The generated C vtable for a [`DriverCrtc`].
@@ -776,3 +806,47 @@ fn as_raw(&self) -> *mut bindings::drm_crtc_state {
         Ok(0)
     })
 }
+
+unsafe extern "C" fn atomic_begin_callback<T: DriverCrtc>(
+    crtc: *mut bindings::drm_crtc,
+    state: *mut bindings::drm_atomic_state,
+) {
+    // SAFETY:
+    // * We're guaranteed `crtc` is of type `Crtc<T>` via type invariants.
+    // * We're guaranteed by DRM that `crtc` is pointing to a valid initialized state.
+    let crtc = unsafe { Crtc::from_raw(crtc) };
+
+    // SAFETY: We're guaranteed by DRM that `state` points to a valid instance of `drm_atomic_state`
+    let state = unsafe { AtomicStateMutator::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_crtc_state(crtc).unwrap_unchecked(),
+        state.get_new_crtc_state(crtc).unwrap_unchecked(),
+    )};
+
+    T::atomic_begin(crtc, old_state, new_state, &state);
+}
+
+unsafe extern "C" fn atomic_flush_callback<T: DriverCrtc>(
+    crtc: *mut bindings::drm_crtc,
+    state: *mut bindings::drm_atomic_state,
+) {
+    // SAFETY:
+    // * We're guaranteed `crtc` is of type `Crtc<T>` via type invariants.
+    // * We're guaranteed by DRM that `crtc` is pointing to a valid initialized state.
+    let crtc = unsafe { Crtc::from_raw(crtc) };
+
+    // SAFETY: We're guaranteed by DRM that `state` points to a valid instance of `drm_atomic_state`
+    let state = unsafe { AtomicStateMutator::new(NonNull::new_unchecked(state)) };
+
+    // SAFETY: We're in an atomic flush callback, so we know that both the new and old state are
+    // present
+    let (old_state, new_state) = unsafe {(
+        state.get_old_crtc_state(crtc).unwrap_unchecked(),
+        state.get_new_crtc_state(crtc).unwrap_unchecked(),
+    )};
+
+    T::atomic_flush(crtc, old_state, new_state, &state);
+}
-- 
2.46.1