linux-kernel - Re: [WIP RFC v2 26/35] WIP: rust: drm/kms: Add RawPlaneState::atomic_helper

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Message-Id: <7148C7F5-6412-44CB-B92A-4ABAE4A4D5C3@collabora.com>
Date: Thu, 28 Nov 2024 11:04:24 -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 26/35] WIP: rust: drm/kms: Add
 RawPlaneState::atomic_helper_check()

Hi Lyude,

> On 30 Sep 2024, at 20:10, Lyude Paul <lyude@...hat.com> wrote:
> 
> Add a binding for drm_atomic_helper_check_plane_state(). Since we want to
> make sure that the user is passing in the new state for a Crtc instead of
> an old state, we explicitly ask for a reference to a BorrowedCrtcState.
> 
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> 
> ---
> 
> TODO:
> * Add support for scaling options

Can / should this be a separate commit? This would allow this one to go in earlier.

> 
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
> rust/kernel/drm/kms/plane.rs | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
> 
> diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
> index 4d16d53179fca..cd5167e6441f1 100644
> --- a/rust/kernel/drm/kms/plane.rs
> +++ b/rust/kernel/drm/kms/plane.rs
> @@ -496,6 +496,31 @@ fn crtc<'a, 'b: 'a>(&'a self) -> Option<&'b OpaqueCrtc<<Self::Plane as ModeObjec
>         // SAFETY: This cast is guaranteed safe by `OpaqueCrtc`s invariants.
>         NonNull::new(self.as_raw().crtc).map(|c| unsafe { OpaqueCrtc::from_raw(c.as_ptr()) })
>     }
> +
> +    /// Run the atomic check helper for this plane and the given CRTC state
> +    fn atomic_helper_check<S>(
> +        &mut self,
> +        crtc_state: &BorrowedCrtcState<'_, S>,
> +        can_position: bool,
> +        can_update_disabled: bool
> +    ) -> Result

Some docs on the arguments would be nice IMHO. Things like `can_position` and `can_update_disabled`
seem a bit opaque.

> +    where
> +        S: FromRawCrtcState,
> +        S::Crtc: AsRawCrtc<Driver = <Self::Plane as ModeObject>::Driver>
> +    {
> +        // SAFETY: We're passing the mutable reference from `self.as_raw_mut()` directly to DRM,
> +        // which is safe.
> +        to_result(unsafe {
> +            bindings::drm_atomic_helper_check_plane_state(
> +                self.as_raw_mut(),
> +                crtc_state.as_raw(),
> +                bindings::DRM_PLANE_NO_SCALING as _, // TODO: add parameters for scaling
> +                bindings::DRM_PLANE_NO_SCALING as _,

No scaling means that you can only select the display’s highest resolution?

> +                can_position,
> +                can_update_disabled
> +            )
> +        })
> +    }
> }
> impl<T: AsRawPlaneState + ?Sized> RawPlaneState for T {}
> 
> -- 
> 2.46.1
> 

Barring the comment above about the docs, this looks good.

— Daniel