[RFC v3 16/33] rust: drm/kms: Add OpaquePlane and OpaquePlaneState

[Lyude Paul <lyude@redhat.com>]

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

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

---

V3:
* Add safety comment to implementation of ModeObject
* Add safety comments to implementation of AsRawPlane
* Implement try_from_opaque() and from_opaque() using a macro
* Add missing upcasts
* Use addr_of_mut!() instead of &mut

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 rust/kernel/drm/kms/plane.rs | 176 ++++++++++++++++++++++++++++++++++-
 1 file changed, 175 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
index d1fabdf42df54..be69dc16c6cc7 100644
--- a/rust/kernel/drm/kms/plane.rs
+++ b/rust/kernel/drm/kms/plane.rs
@@ -4,7 +4,7 @@
 //!
 //! C header: [`include/drm/drm_plane.h`](srctree/include/drm/drm_plane.h)
 
-use super::{KmsDriver, ModeObject, StaticModeObject, UnregisteredKmsDevice};
+use super::{KmsDriver, ModeObject, ModeObjectVtable, StaticModeObject, UnregisteredKmsDevice};
 use crate::{
     alloc::KBox,
     bindings,
@@ -169,6 +169,25 @@ fn deref(&self) -> &Self::Target {
     }
 }
 
+// SAFETY: `funcs` is initialized when the plane is allocated
+unsafe impl<T: DriverPlane> ModeObjectVtable for Plane<T> {
+    type Vtable = bindings::drm_plane_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        // SAFETY: `as_raw()` always returns a valid plane pointer
+        unsafe { *self.as_raw() }.funcs
+    }
+}
+
+impl<T: DriverPlane> Plane<T> {
+    super::impl_from_opaque_mode_obj! {
+        fn <'a, D>(&'a OpaquePlane<D>) -> &'a Self;
+        use
+            T as DriverPlane,
+            D as KmsDriver
+    }
+}
+
 /// A [`Plane`] that has not yet been registered with userspace.
 ///
 /// KMS registration is single-threaded, so this object is not thread-safe.
@@ -396,6 +415,84 @@ fn mask(&self) -> u32 {
 }
 impl<T: AsRawPlane> RawPlane for 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> {}
+
+// SAFETY:
+// * Via our type variants our data layout is identical to `drm_plane`
+// * Since we don't expose `plane` to users before it has been initialized, this and our data
+//   layout ensure that `as_raw()` always returns a valid pointer to a `drm_plane`.
+unsafe impl<T: KmsDriver> AsRawPlane for OpaquePlane<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() }
+    }
+}
+
+// SAFETY: We only expose this object to users directly after KmsDriver::create_objects has been
+// called.
+unsafe impl<T: KmsDriver> ModesettablePlane for OpaquePlane<T> {
+    type State = OpaquePlaneState<T>;
+}
+
+// SAFETY: We don't expose OpaquePlane<T> to users before `base` is initialized in
+// Plane::<T>::new(), so `raw_mode_obj` always returns a valid pointer to a
+// bindings::drm_mode_object.
+unsafe 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 { addr_of_mut!((*self.as_raw()).base) }
+    }
+}
+
+// SAFETY: Planes do not have a refcount
+unsafe impl<T: KmsDriver> StaticModeObject for OpaquePlane<T> {}
+
+// SAFETY: `funcs` is initialized when the plane is allocated
+unsafe impl<T: KmsDriver> ModeObjectVtable for OpaquePlane<T> {
+    type Vtable = bindings::drm_plane_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        // SAFETY: `as_raw()` always returns a valid pointer to a plane
+        unsafe { *self.as_raw() }.funcs
+    }
+}
+
+// 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.
@@ -572,6 +669,83 @@ fn deref_mut(&mut self) -> &mut Self::Target {
     }
 }
 
+// SAFETY: Shares the safety guarantee of Plane<T>'s vtable impl
+unsafe impl<T: DriverPlaneState> ModeObjectVtable for PlaneState<T> {
+    type Vtable = bindings::drm_plane_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        self.plane().vtable()
+    }
+}
+
+impl<T: DriverPlaneState> PlaneState<T> {
+    super::impl_from_opaque_mode_obj! {
+        fn <'a, D, P>(&'a OpaquePlaneState<D>) -> &'a Self
+        where
+            T: DriverPlaneState<Plane = P>;
+        use
+            P as DriverPlane,
+            D as KmsDriver
+    }
+}
+
+/// 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.
+///
+/// # 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() }
+    }
+}
+
+// SAFETY: Shares the safety guarantee of OpaquePlane<T>'s vtable impl
+unsafe impl<T: KmsDriver> ModeObjectVtable for OpaquePlaneState<T> {
+    type Vtable = bindings::drm_plane_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        self.plane().vtable()
+    }
+}
+
 unsafe extern "C" fn plane_destroy_callback<T: DriverPlane>(plane: *mut bindings::drm_plane) {
     // SAFETY: DRM guarantees that `plane` points to a valid initialized `drm_plane`.
     unsafe { bindings::drm_plane_cleanup(plane) };
-- 
2.48.1