Message-Id: <522F0A49-6A38-40F3-B287-632D1F238223@collabora.com>
Date: Thu, 28 Nov 2024 11:33:41 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Lyude Paul <lyude@...hat.com>
Cc: dri-devel@...ts.freedesktop.org,
 rust-for-linux@...r.kernel.org,
 Asahi Lina <lina@...hilina.net>,
 Danilo Krummrich <dakr@...nel.org>,
 mcanal@...lia.com,
 airlied@...hat.com,
 zhiw@...dia.com,
 cjia@...dia.com,
 jhubbard@...dia.com,
 Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Wedson Almeida Filho <wedsonaf@...il.com>,
 Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...sung.com>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [WIP RFC v2 30/35] rust: drm/kms: Add DriverCrtc::atomic_enable()
 and atomic_disable()

Hi Lyude

> On 30 Sep 2024, at 20:10, Lyude Paul <lyude@...hat.com> wrote:
> 
> Optional trait methods for implementing the atomic_enable and
> atomic_disable callbacks of a CRTC.
> 
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
> rust/kernel/drm/kms/crtc.rs | 76 ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 74 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/drm/kms/crtc.rs b/rust/kernel/drm/kms/crtc.rs
> index a4e955364bd8c..ef1b331f742d0 100644
> --- a/rust/kernel/drm/kms/crtc.rs
> +++ b/rust/kernel/drm/kms/crtc.rs
> @@ -80,8 +80,8 @@ pub trait DriverCrtc: Send + Sync + Sized {
>         },
> 
>         helper_funcs: bindings::drm_crtc_helper_funcs {
> -            atomic_disable: None,
> -            atomic_enable: None,
> +            atomic_disable: if Self::HAS_ATOMIC_DISABLE { Some(atomic_disable_callback::<Self>) } else { None },
> +            atomic_enable: if Self::HAS_ATOMIC_ENABLE { Some(atomic_enable_callback::<Self>) } else { None },
>             atomic_check: if Self::HAS_ATOMIC_CHECK { Some(atomic_check_callback::<Self>) } else { None },
>             dpms: None,
>             commit: None,
> @@ -162,6 +162,34 @@ fn atomic_flush(
>     ) {
>         build_error::build_error("This should never be reachable")
>     }
> +
> +    /// The optional [`drm_crtc_helper_funcs.atomic_enable`] hook.
> +    ///
> +    /// This hook will be called before enabling a [`Crtc`] in an atomic commit.
> +    ///
> +    /// [`drm_crtc_helper_funcs.atomic_enable`]: srctree/include/drm/drm_modeset_helper_vtables.h
> +    fn atomic_enable(
> +        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 optional [`drm_crtc_helper_funcs.atomic_disable`] hook.
> +    ///
> +    /// This hook will be called before disabling a [`Crtc`] in an atomic commit.
> +    ///
> +    /// [`drm_crtc_helper_funcs.atomic_disable`]: srctree/include/drm/drm_modeset_helper_vtables.h
> +    fn atomic_disable(
> +        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 previous patches.

> 
> /// The generated C vtable for a [`DriverCrtc`].
> @@ -850,3 +878,47 @@ fn as_raw(&self) -> *mut bindings::drm_crtc_state {
> 
>     T::atomic_flush(crtc, old_state, new_state, &state);
> }
> +
> +unsafe extern "C" fn atomic_enable_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: DRM never passes an invalid ptr for `state`
> +    let state = unsafe { AtomicStateMutator::new(NonNull::new_unchecked(state)) };
> +
> +    // SAFETY: We're in an atomic enable 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_enable(crtc, old_state, new_state, &state);
> +}
> +
> +unsafe extern "C" fn atomic_disable_callback<T: DriverCrtc>(
> +    crtc: *mut bindings::drm_crtc,
> +    state: *mut bindings::drm_atomic_state,
> +) {
> +    // SAFETY:
> +    // * We're guaranteed `crtc` points to a valid instance of `drm_crtc`
> +    // * We're guaranteed that `crtc` is of type `Plane<T>` by `DriverPlane`s type invariants.
> +    let crtc = unsafe { Crtc::from_raw(crtc) };
> +
> +    // SAFETY: We're guaranteed that `state` points to a valid `drm_crtc_state` by DRM
> +    let state = unsafe { AtomicStateMutator::new(NonNull::new_unchecked(state)) };
> +
> +    // SAFETY: We're in an atomic commit 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_disable(crtc, old_state, new_state, &state);
> +}
> -- 
> 2.46.1
> 
> 

FYI, they all look good to me. It’s just a matter of figuring out this build_error pattern and whether it’s
really needed.

— Daniel

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