[WIP RFC v2 15/35] WIP: rust: drm/kms: Add OpaquePlane and OpaquePlaneState

[Lyude Paul]

Same thing as OpaqueCrtc and OpaqueCrtcState, but for plane states now.

Signed-off-by: Lyude Paul <lyude at redhat.com>

---

TODO:
* Finish adding upcast functions.

Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 rust/kernel/drm/kms/plane.rs | 143 +++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)

diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
index 3040c4546b121..3ace487316d46 100644
--- a/rust/kernel/drm/kms/plane.rs
+++ b/rust/kernel/drm/kms/plane.rs
@@ -217,6 +217,43 @@ pub fn new<'a, 'b: 'a, const FMT_COUNT: usize, const MOD_COUNT: usize>(
         // SAFETY: We don't move anything
         Ok(unsafe { &*Box::into_raw(Pin::into_inner_unchecked(this)) })
     }
+
+    /// Attempt to convert an [`OpaquePlane`] into a fully qualified [`Plane`].
+    ///
+    /// This checks if the given [`OpaquePlane`] uses the same [`DriverPlane`] implementation, and
+    /// returns the [`OpaquePlane`] as a [`Plane`] object if so.
+    pub fn try_from_opaque<'a, D>(opaque: &'a OpaquePlane<D>) -> Option<&'a Self>
+    where
+        D: KmsDriver,
+        T: DriverPlane<Driver = D>
+    {
+        // SAFETY: The vtables for a `Plane` are initialized by the time that we expose `Plane`
+        // objects to users, and their values are invariant throughout the lifetime of the device.
+        let funcs = unsafe { (*opaque.plane.get()).funcs };
+
+        // SAFETY: We just guaranteed that the opaque plane shares our vtable pointers, which means
+        // it must belong to our `DriverPlane` implementation. As well, all `Plane<DriverPlane>`
+        // objects start with an identical data layout to `OpaquePlane`
+        ptr::eq(funcs, &T::OPS.funcs).then(|| unsafe { mem::transmute(opaque) })
+    }
+
+    /// Convert a [`OpaquePlane`] into its fully qualified [`Plane`].
+    ///
+    /// This is an infallible version of [`Self::try_from_opaque`]. This function is mainly useful
+    /// for drivers where only a single [`DriverPlane`] implementation exists.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the underlying [`Plane`] which contains the provided
+    /// [`OpaquePlane`] does not belong to the same [`DriverPlane`] implementation.
+    pub fn from_opaque<'a, D>(opaque: &'a OpaquePlane<D>) -> &'a Self
+    where
+        D: KmsDriver,
+        T: DriverPlane<Driver = D>
+    {
+        Self::try_from_opaque(opaque)
+            .expect("Passed OpaquePlane does not share this DriverPlane implementation")
+    }
 }
 
 /// A trait implemented by any type that acts as a [`struct drm_plane`] interface.
@@ -275,6 +312,63 @@ unsafe impl<T: DriverPlane> Send for Plane<T> {}
 // SAFETY: Our interface is thread-safe.
 unsafe impl<T: DriverPlane> Sync for Plane<T> {}
 
+/// A [`struct drm_plane`] without a known [`DriverPlane`] implementation.
+///
+/// This is mainly for situations where our bindings can't infer the [`DriverPlane`] implementation
+/// for a [`struct drm_plane`] automatically. It is identical to [`Plane`], except that it does not
+/// provide access to the driver's private data.
+///
+/// It may be upcasted to a full [`Plane`] using [`Plane::from_opaque`] or
+/// [`Plane::try_from_opaque`].
+///
+/// # Invariants
+///
+/// - `plane` is initialized for as long as this object is made available to users.
+/// - The data layout of this structure is equivalent to [`struct drm_plane`].
+///
+/// [`struct drm_plane`]: srctree/include/drm/drm_plane.h
+#[repr(transparent)]
+pub struct OpaquePlane<T: KmsDriver> {
+    plane: Opaque<bindings::drm_plane>,
+    _p: PhantomData<T>,
+}
+
+impl<T: KmsDriver> Sealed for OpaquePlane<T> {}
+
+impl<T: KmsDriver> AsRawPlane for OpaquePlane<T> {
+    type State = OpaquePlaneState<T>;
+
+    fn as_raw(&self) -> *mut bindings::drm_plane {
+        self.plane.get()
+    }
+
+    unsafe fn from_raw<'a>(ptr: *mut bindings::drm_plane) -> &'a Self {
+        // SAFETY: Our data layout is identical to `bindings::drm_plane`
+        unsafe { &*ptr.cast() }
+    }
+}
+
+impl<T: KmsDriver> ModeObject for OpaquePlane<T> {
+    type Driver = T;
+
+    fn drm_dev(&self) -> &Device<Self::Driver> {
+        // SAFETY: DRM planes exist for as long as the device does, so this pointer is always valid
+        unsafe { Device::borrow((*self.as_raw()).dev) }
+    }
+
+    fn raw_mode_obj(&self) -> *mut bindings::drm_mode_object {
+        // SAFETY: We don't expose DRM planes to users before `base` is initialized
+        unsafe { &mut ((*self.as_raw()).base) }
+    }
+}
+
+// SAFETY: Planes do not have a refcount
+unsafe impl<T: KmsDriver> StaticModeObject for OpaquePlane<T> {}
+
+// SAFETY: Our plane interfaces are guaranteed to be thread-safe
+unsafe impl<T: KmsDriver> Send for OpaquePlane<T> {}
+unsafe impl<T: KmsDriver> Sync for OpaquePlane<T> {}
+
 /// A trait implemented by any type which can produce a reference to a [`struct drm_plane_state`].
 ///
 /// This is implemented internally by DRM.
@@ -419,6 +513,55 @@ fn deref_mut(&mut self) -> &mut Self::Target {
     }
 }
 
+/// A [`struct drm_plane_state`] without a known [`DriverPlaneState`] implementation.
+///
+/// This is mainly for situations where our bindings can't infer the [`DriverPlaneState`]
+/// implementation for a [`struct drm_plane_state`] automatically. It is identical to [`Plane`],
+/// except that it does not provide access to the driver's private data.
+///
+/// TODO: Add upcast functions
+///
+/// # Invariants
+///
+/// - The DRM C API and our interface guarantees that only the user has mutable access to `state`,
+///   up until [`drm_atomic_helper_commit_hw_done`] is called. Therefore, `plane` follows rust's
+///   data aliasing rules and does not need to be behind an [`Opaque`] type.
+/// - `state` is initialized for as long as this object is exposed to users.
+/// - The data layout of this structure is identical to [`struct drm_plane_state`].
+///
+/// [`struct drm_plane_state`]: srctree/include/drm/drm_plane.h
+/// [`drm_atomic_helper_commit_hw_done`]: srctree/include/drm/drm_atomic_helper.h
+#[repr(transparent)]
+pub struct OpaquePlaneState<T: KmsDriver> {
+    state: bindings::drm_plane_state,
+    _p: PhantomData<T>,
+}
+
+impl<T: KmsDriver> AsRawPlaneState for OpaquePlaneState<T> {
+    type Plane = OpaquePlane<T>;
+}
+
+impl<T: KmsDriver> private::AsRawPlaneState for OpaquePlaneState<T> {
+    fn as_raw(&self) -> &bindings::drm_plane_state {
+        &self.state
+    }
+
+    unsafe fn as_raw_mut(&mut self) -> &mut bindings::drm_plane_state {
+        &mut self.state
+    }
+}
+
+impl<T: KmsDriver> FromRawPlaneState for OpaquePlaneState<T> {
+    unsafe fn from_raw<'a>(ptr: *const bindings::drm_plane_state) -> &'a Self {
+        // SAFETY: Our data layout is identical to `ptr`
+        unsafe { &*ptr.cast() }
+    }
+
+    unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_plane_state) -> &'a mut Self {
+        // SAFETY: Our data layout is identical to `ptr`
+        unsafe { &mut *ptr.cast() }
+    }
+}
 unsafe extern "C" fn plane_destroy_callback<T: DriverPlane>(
     plane: *mut bindings::drm_plane
 ) {
-- 
2.46.1