linux-kernel - Re: [WIP RFC v2 19/35] WIP: rust: drm/kms: Add OpaqueEncoder

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Message-Id: <C8281624-85B3-423E-8451-354F4BC16B97@collabora.com>
Date: Wed, 27 Nov 2024 16:35:30 -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 19/35] WIP: rust: drm/kms: Add OpaqueEncoder

Hi Lyude,

> On 30 Sep 2024, at 20:10, Lyude Paul <lyude@...hat.com> wrote:
> 
> Same thing as OpaquePlane, but for encoders now.
> 
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> 
> ---
> 
> TODO:
> * Add upcast functions for this
> 
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
> rust/kernel/drm/kms/encoder.rs | 55 ++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
> 
> diff --git a/rust/kernel/drm/kms/encoder.rs b/rust/kernel/drm/kms/encoder.rs
> index 3ae597093645e..71fae45d2d651 100644
> --- a/rust/kernel/drm/kms/encoder.rs
> +++ b/rust/kernel/drm/kms/encoder.rs
> @@ -235,6 +235,61 @@ pub fn new<'a, 'b: 'a>(
>     }
> }
> 
> +/// A [`struct drm_encoder`] without a known [`DriverEncoder`] implementation.
> +///
> +/// This is mainly for situations where our bindings can't infer the [`DriverEncoder`] implementation
> +/// for a [`struct drm_encoder`] automatically. It is identical to [`Encoder`], except that it does not
> +/// provide access to the driver's private data.
> +///
> +/// TODO: Add functions for upcasting.
> +///
> +/// # Invariants
> +///
> +/// Same as [`Encoder`].
> +#[repr(transparent)]
> +pub struct OpaqueEncoder<T: KmsDriver> {
> +    encoder: Opaque<bindings::drm_encoder>,
> +    _p: PhantomData<T>,
> +}
> +
> +impl<T: KmsDriver> Sealed for OpaqueEncoder<T> {}
> +
> +// SAFETY: All of our encoder interfaces are thread-safe
> +unsafe impl<T: KmsDriver> Send for OpaqueEncoder<T> {}
> +
> +// SAFETY: All of our encoder interfaces are thread-safe
> +unsafe impl<T: KmsDriver> Sync for OpaqueEncoder<T> {}
> +
> +impl<T: KmsDriver> ModeObject for OpaqueEncoder<T> {
> +    type Driver = T;
> +
> +    fn drm_dev(&self) -> &Device<Self::Driver> {
> +        // SAFETY: DRM encoders exist for as long as the device does, so this pointer is always
> +        // valid
> +        unsafe { Device::borrow((*self.encoder.get()).dev) }
> +    }
> +
> +    fn raw_mode_obj(&self) -> *mut bindings::drm_mode_object {
> +        // SAFETY: We don't expose Encoder<T> to users before it's initialized, so `base` is always
> +        // initialized
> +        unsafe { addr_of_mut!((*self.encoder.get()).base) }
> +    }
> +}
> +
> +// SAFETY: Encoders do not have a refcount
> +unsafe impl<T: KmsDriver> StaticModeObject for OpaqueEncoder<T> {}
> +
> +impl<T: KmsDriver> AsRawEncoder for OpaqueEncoder<T> {
> +    fn as_raw(&self) -> *mut bindings::drm_encoder {
> +        self.encoder.get()
> +    }
> +
> +    unsafe fn from_raw<'a>(ptr: *mut bindings::drm_encoder) -> &'a Self {
> +        // SAFETY: Our data layout is identical to `bindings::drm_encoder`
> +        unsafe { &*ptr.cast() }
> +    }
> +}
> +
> unsafe extern "C" fn encoder_destroy_callback<T: DriverEncoder>(
>     encoder: *mut bindings::drm_encoder
> ) {
> -- 
> 2.46.1
> 

No `from_opaque` and `try_from_opaque` like the previous patches?

— Daniel