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

[Daniel Almeida]

Hi Lyude,

> On 30 Sep 2024, at 20:10, Lyude Paul <lyude at redhat.com> wrote:
> 
> 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")
> +    }
> }

Same comment here as in the previous patches, i.e.: if this is optional, why do we have a
default implementation with build_error?

> 
> /// 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
> 
> 


— Daniel