> On 30 Sep 2024, at 20:10, Lyude Paul <lyude@xxxxxxxxxx> wrote:
>
> A mandatory trait method used for implementing DRM's atomic plane update
> callback.
>
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> ---
> rust/kernel/drm/kms/plane.rs | 39 +++++++++++++++++++++++++++++++++++-
> 1 file changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
> index d6e11a65cc101..506ed5ced1270 100644
> --- a/rust/kernel/drm/kms/plane.rs
> +++ b/rust/kernel/drm/kms/plane.rs
> @@ -75,7 +75,7 @@ pub trait DriverPlane: Send + Sync + Sized {
> begin_fb_access: None, // TODO: someday?
> end_fb_access: None, // TODO: someday?
> atomic_check: None,
> - atomic_update: None,
> + atomic_update: if Self::HAS_ATOMIC_UPDATE { Some(atomic_update_callback::<Self>) } else { None },
> atomic_enable: None, // TODO
> atomic_disable: None, // TODO
> atomic_async_check: None, // TODO
> @@ -103,6 +103,21 @@ pub trait DriverPlane: Send + Sync + Sized {
> ///
> /// Drivers may use this to instantiate their [`DriverPlane`] object.
> fn new(device: &Device<Self::Driver>, args: Self::Args) -> impl PinInit<Self, Error>;
> +
> + /// The optional [`drm_plane_helper_funcs.atomic_update`] hook for this plane.
> + ///
> + /// Drivers may use this to customize the atomic update phase of their [`Plane`] objects. If not
> + /// specified, this function is a no-op.
> + ///
> + /// [`drm_plane_helper_funcs.atomic_update`]: srctree/include/drm/drm_modeset_helper_vtables.h
> + fn atomic_update(
> + plane: &Plane<Self>,
> + new_state: BorrowedPlaneState<'_, PlaneState<Self::State>>,
> + old_state: &PlaneState<Self::State>,
> + state: &AtomicStateMutator<Self::Driver>
> + ) {
> + build_error::build_error("This should not be reachable")
> + }
One more comment. If this is mandatory, why not omit this default here to get the compiler to enforce
the implementation of this fn by drivers?
> }
>
> /// The generated C vtable for a [`DriverPlane`].
> @@ -757,3 +772,25 @@ fn deref_mut(&mut self) -> &mut Self::Target {
> // - The cast to `drm_plane_state` is safe via `PlaneState`s type invariants.
> unsafe { bindings::__drm_atomic_helper_plane_reset(plane, Box::into_raw(new).cast()) };
> }
> +
> +unsafe extern "C" fn atomic_update_callback<T: DriverPlane>(
> + plane: *mut bindings::drm_plane,
> + state: *mut bindings::drm_atomic_state,
> +) {
> + // 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: DRM guarantees `state` points to a valid `drm_atomic_state`
> + let state = unsafe { AtomicStateMutator::new(NonNull::new_unchecked(state)) };
> +
> + // SAFETY: Since we are in the atomic update callback, we're guaranteed by DRM that both the old
> + // and new atomic state are present within `state`
> + let (old_state, new_state) = unsafe {(
> + state.get_old_plane_state(plane).unwrap_unchecked(),
> + state.get_new_plane_state(plane).unwrap_unchecked(),
> + )};
> +
> + T::atomic_update(plane, new_state, old_state, &state);
> +}
> --
> 2.46.1
>
>
— Daniel
