Re: [RFC v3 21/33] rust: drm/kms: Add DriverPlane::atomic_check()

[Maxime Ripard <mripard@kernel.org>]

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On Wed, Mar 05, 2025 at 05:59:37PM -0500, Lyude Paul wrote:
> Optional trait method for implementing a plane's atomic_check().
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> 
> ---
> V3:
> * Document ManuallyDrop uses better
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
>  rust/kernel/drm/kms/plane.rs | 53 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 50 insertions(+), 3 deletions(-)
> 
> diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
> index b090aebc35649..f3adc30c17489 100644
> --- a/rust/kernel/drm/kms/plane.rs
> +++ b/rust/kernel/drm/kms/plane.rs
> @@ -11,7 +11,7 @@
>      alloc::KBox,
>      bindings,
>      drm::{device::Device, fourcc::*},
> -    error::{to_result, Error},
> +    error::{from_result, to_result, Error},
>      init::Zeroable,
>      prelude::*,
>      private::Sealed,
> @@ -20,7 +20,7 @@
>  use core::{
>      cell::Cell,
>      marker::*,
> -    mem,
> +    mem::{self, ManuallyDrop},
>      ops::*,
>      pin::Pin,
>      ptr::{addr_of_mut, null, null_mut, NonNull},
> @@ -69,7 +69,11 @@ pub trait DriverPlane: Send + Sync + Sized {
>              cleanup_fb: None,
>              begin_fb_access: None,
>              end_fb_access: None,
> -            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 {
> @@ -117,6 +121,21 @@ 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: PlaneStateMutator<'_, PlaneState<Self::State>>,
> +        _old_state: &PlaneState<Self::State>,
> +        _state: &AtomicStateComposer<Self::Driver>,
> +    ) -> Result {
> +        build_error::build_error("This should not be reachable")
> +    }

I think it was the other way around for CRTCs between old_state and
new_state? I still believe we should get rid of both, but we need to be
consistent at least :)

Maxime

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