[WIP RFC v2 14/35] WIP: rust: drm/kms: Add OpaqueCrtc and OpaqueCrtcState

[Lyude Paul <lyude@redhat.com>]

This is the same thing as OpaqueConnector and OpaqueConnectorState, but for
CRTCs now.

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

---

TODO:
* Add upcast functions

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 rust/kernel/drm/kms/crtc.rs | 131 ++++++++++++++++++++++++++++++++++++
 1 file changed, 131 insertions(+)

diff --git a/rust/kernel/drm/kms/crtc.rs b/rust/kernel/drm/kms/crtc.rs
index d84db49948380..1a3c9c448afcc 100644
--- a/rust/kernel/drm/kms/crtc.rs
+++ b/rust/kernel/drm/kms/crtc.rs
@@ -234,6 +234,41 @@ pub fn new<'a, 'b: 'a, P, C>(
         // SAFETY: We don't move anything
         Ok(unsafe { &*Box::into_raw(Pin::into_inner_unchecked(this)) })
     }
+
+    /// Attempt to convert an [`OpaqueCrtc`] into a fully qualified [`Crtc`].
+    ///
+    /// This checks if the given [`OpaqueCrtc`] uses the same [`DriverCrtc`] implementation, and
+    /// returns the [`OpaqueCrtc`] as a [`Crtc`] object if so.
+    pub fn try_from_opaque<'a, D>(opaque: &'a OpaqueCrtc<D>) -> Option<&'a Self>
+    where
+        D: KmsDriver,
+        T: DriverCrtc<Driver = D>
+    {
+        // SAFETY: The vtables for a `Crtc` are initialized throughout the lifetime of the object
+        let funcs = unsafe { (*opaque.crtc.get()).funcs };
+
+        // SAFETY: We only perform this transmutation if the opaque CRTC shares our vtable pointers,
+        // so the underlying `Crtc` must share our data layout.
+        ptr::eq(funcs, &T::OPS.funcs).then(|| unsafe { mem::transmute(opaque) })
+    }
+
+    /// Convert a [`OpaqueCrtc`] into its fully qualified [`Crtc`].
+    ///
+    /// This is an infallible version of [`Self::try_from_opaque`]. This function is mainly useful
+    /// for drivers where only a single [`DriverCrtc`] implementation exists.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the underlying CRTC in the provided [`OpaqueCrtc`] does not
+    /// belong to the same [`DriverCrtc`] implementation.
+    pub fn from_opaque<'a, D>(opaque: &'a OpaqueCrtc<D>) -> &'a Self
+    where
+        D: KmsDriver,
+        T: DriverCrtc<Driver = D>
+    {
+        Self::try_from_opaque(opaque)
+            .expect("Passed OpaqueCrtc does not share this DriverCrtc implementation")
+    }
 }
 
 /// A trait implemented by any type that acts as a [`struct drm_crtc`] interface.
@@ -267,6 +302,66 @@ unsafe fn from_raw<'a>(ptr: *mut bindings::drm_crtc) -> &'a Self {
     }
 }
 
+/// A [`struct drm_crtc`] without a known [`DriverCrtc`] implementation.
+///
+/// This is mainly for situations where our bindings can't infer the [`DriverCrtc`] implementation
+/// for a [`struct drm_crtc`] automatically. It is identical to [`Crtc`], except that it does not
+/// provide access to the driver's private data.
+///
+/// It may be upcasted to a full [`Crtc`] using [`Crtc::from_opaque`] or
+/// [`Crtc::try_from_opaque`].
+///
+/// # Invariants
+///
+/// - `crtc` is initialized for as long as this object is made available to users.
+/// - The data layout of this structure is equivalent to [`struct drm_crtc`].
+///
+/// [`struct drm_crtc`]: srctree/include/drm/drm_crtc.h
+#[repr(transparent)]
+pub struct OpaqueCrtc<T: KmsDriver> {
+    crtc: Opaque<bindings::drm_crtc>,
+    _p: PhantomData<T>
+}
+
+impl<T: KmsDriver> Sealed for OpaqueCrtc<T> {}
+
+impl<T: KmsDriver> AsRawCrtc for OpaqueCrtc<T> {
+    type State = OpaqueCrtcState<T>;
+
+    fn as_raw(&self) -> *mut bindings::drm_crtc {
+        self.crtc.get()
+    }
+
+    unsafe fn from_raw<'a>(ptr: *mut bindings::drm_crtc) -> &'a Self {
+        // SAFETY: Our data layout starts with `bindings::drm_crtc`
+        unsafe { &*ptr.cast() }
+    }
+}
+
+impl<T: KmsDriver> ModeObject for OpaqueCrtc<T> {
+    type Driver = T;
+
+    fn drm_dev(&self) -> &Device<Self::Driver> {
+        // SAFETY: The parent device for a DRM connector will never outlive the connector, and this
+        // pointer is invariant through the lifetime of the connector
+        unsafe { Device::borrow((*self.as_raw()).dev) }
+    }
+
+    fn raw_mode_obj(&self) -> *mut bindings::drm_mode_object {
+        // SAFETY: We don't expose DRM connectors to users before `base` is initialized
+        unsafe { addr_of_mut!((*self.as_raw()).base) }
+    }
+}
+
+// SAFETY: CRTCs are non-refcounted modesetting objects
+unsafe impl<T: KmsDriver> StaticModeObject for OpaqueCrtc<T> {}
+
+// SAFETY: Our CRTC interface is guaranteed to be thread-safe
+unsafe impl<T: KmsDriver> Send for OpaqueCrtc<T> {}
+
+// SAFETY: Our CRTC interface is guaranteed to be thread-safe
+unsafe impl<T: KmsDriver> Sync for OpaqueCrtc<T> {}
+
 unsafe impl Zeroable for bindings::drm_crtc_state { }
 
 impl<T: DriverCrtcState> Sealed for CrtcState<T> {}
@@ -400,6 +495,42 @@ unsafe fn from_raw<'a>(ptr: *const bindings::drm_crtc_state) -> &'a Self {
     }
 }
 
+/// A [`struct drm_crtc_state`] without a known [`DriverCrtcState`] implementation.
+///
+/// This is mainly for situations where our bindings can't infer the [`DriverCrtcState`]
+/// implementation for a [`struct drm_crtc_state`] automatically. It is identical to [`Crtc`],
+/// except that it does not provide access to the driver's private data.
+///
+/// TODO: Add upcast functions
+///
+/// # Invariants
+///
+/// - `state` is initialized for as long as this object is exposed to users.
+/// - The data layout of this type is identical to [`struct drm_crtc_state`].
+///
+/// [`struct drm_crtc_state`]: srctree/include/drm/drm_crtc.h
+#[repr(transparent)]
+pub struct OpaqueCrtcState<T: KmsDriver> {
+    state: Opaque<bindings::drm_crtc_state>,
+    _p: PhantomData<T>
+}
+
+impl<T: KmsDriver> AsRawCrtcState for OpaqueCrtcState<T> {
+    type Crtc = OpaqueCrtc<T>;
+}
+
+impl<T: KmsDriver> private::AsRawCrtcState for OpaqueCrtcState<T> {
+    fn as_raw(&self) -> *mut bindings::drm_crtc_state {
+        self.state.get()
+    }
+}
+
+impl<T: KmsDriver> FromRawCrtcState for OpaqueCrtcState<T> {
+    unsafe fn from_raw<'a>(ptr: *const bindings::drm_crtc_state) -> &'a Self {
+        // SAFETY: Our data layout is identical to `bindings::drm_crtc_state`
+        unsafe { &*(ptr.cast()) }
+    }
+}
 unsafe extern "C" fn crtc_destroy_callback<T: DriverCrtc>(
     crtc: *mut bindings::drm_crtc
 ) {
-- 
2.46.1