[WIP RFC v2 13/35] WIP: rust: drm/kms: Add OpaqueConnector and OpaqueConnectorState

[Lyude Paul <lyude@redhat.com>]

Since we allow drivers to have multiple implementations of DriverConnector
and DriverConnectorState (in C, the equivalent of this is having multiple
structs which embed drm_connector) - there are some situations we will run
into where it's not possible for us to know the corresponding
DriverConnector or DriverConnectorState for a given connector. The most
obvious one is iterating through all connectors on a KMS device.

So, take advantage of the various connector traits we added to introduce
OpaqueConnector<> and OpaqueConnectorState<> which both can be used as a
DRM connector and connector state respectively without needing to know the
corresponding traits.

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

---

TODO:
* Add upcast functions for these types

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 rust/kernel/drm/kms/connector.rs | 108 +++++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)

diff --git a/rust/kernel/drm/kms/connector.rs b/rust/kernel/drm/kms/connector.rs
index ec842ebc111ae..98ac7fb781d4e 100644
--- a/rust/kernel/drm/kms/connector.rs
+++ b/rust/kernel/drm/kms/connector.rs
@@ -359,6 +359,64 @@ unsafe fn from_raw<'a>(ptr: *mut bindings::drm_connector) -> &'a Self {
     T::get_modes(connector.guard(&guard), &guard)
 }
 
+/// A [`struct drm_connector`] without a known [`DriverConnector`] implementation.
+///
+/// This is mainly for situations where our bindings can't infer the [`DriverConnector`]
+/// implementation for a [`struct drm_connector`] automatically. It is identical to [`Connector`],
+/// except that it does not provide access to the driver's private data.
+///
+/// TODO: Add upcast methods for this
+///
+/// # Invariants
+///
+/// - `connector` is initialized for as long as this object is exposed to users.
+/// - The data layout of this type is equivalent to [`struct drm_connector`].
+///
+/// [`struct drm_connector`]: srctree/include/drm/drm_connector.h
+#[repr(transparent)]
+pub struct OpaqueConnector<T: KmsDriver> {
+    connector: Opaque<bindings::drm_connector>,
+    _p: PhantomData<T>
+}
+
+impl<T: KmsDriver> Sealed for OpaqueConnector<T> {}
+
+impl<T: KmsDriver> AsRawConnector for OpaqueConnector<T> {
+    type Driver = T;
+    type State = OpaqueConnectorState<T>;
+
+    fn as_raw(&self) -> *mut bindings::drm_connector {
+        self.connector.get()
+    }
+
+    unsafe fn from_raw<'a>(ptr: *mut bindings::drm_connector) -> &'a Self {
+        // SAFETY: Our data layout is identical to `bindings::drm_connector`
+        unsafe { &*ptr.cast() }
+    }
+}
+
+impl<T: KmsDriver> ModeObject for OpaqueConnector<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 { &mut (*self.as_raw()).base }
+    }
+}
+
+// SAFETY: Connectors are reference counted mode objects
+unsafe impl<T: KmsDriver> RcModeObject for OpaqueConnector<T> {}
+
+// SAFETY: Our connector interfaces are guaranteed to be thread-safe
+unsafe impl<T: KmsDriver> Send for OpaqueConnector<T> {}
+unsafe impl<T: KmsDriver> Sync for OpaqueConnector<T> {}
+
 /// A privileged [`Connector`] obtained while holding a [`ModeConfigGuard`].
 ///
 /// This provides access to various methods for [`Connector`] that must happen under lock, such as
@@ -537,6 +595,56 @@ unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_connector_state) -> &'a mut S
     }
 }
 
+/// A [`struct drm_connector_state`] without a known [`DriverConnectorState`] implementation.
+///
+/// This is mainly for situations where our bindings can't infer the [`DriverConnectorState`]
+/// implementation for a [`struct drm_connector_state`] automatically. It is identical to
+/// [`Connector`], 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_connector_state`].
+/// - 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, `connector` follows rust's
+///   data aliasing rules and does not need to be behind an [`Opaque`] type.
+///
+/// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+/// [`drm_atomic_helper_commit_hw_done`]: srctree/include/drm/drm_atomic_helper.h
+#[repr(transparent)]
+pub struct OpaqueConnectorState<T: KmsDriver> {
+    state: bindings::drm_connector_state,
+    _p: PhantomData<T>
+}
+
+impl<T: KmsDriver> AsRawConnectorState for OpaqueConnectorState<T> {
+    type Connector = OpaqueConnector<T>;
+}
+
+impl<T: KmsDriver> private::AsRawConnectorState for OpaqueConnectorState<T> {
+    fn as_raw(&self) -> &bindings::drm_connector_state {
+        &self.state
+    }
+
+    unsafe fn as_raw_mut(&mut self) -> &mut bindings::drm_connector_state {
+        &mut self.state
+    }
+}
+
+impl<T: KmsDriver> FromRawConnectorState for OpaqueConnectorState<T> {
+    unsafe fn from_raw<'a>(ptr: *const bindings::drm_connector_state) -> &'a Self {
+        // SAFETY: Our data layout is identical to `bindings::drm_connector_state`
+        unsafe { &*ptr.cast() }
+    }
+
+    unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_connector_state) -> &'a mut Self {
+        // SAFETY: Our data layout is identical to `bindings::drm_connector_state`
+        unsafe { &mut *ptr.cast() }
+    }
+}
+
 unsafe extern "C" fn atomic_duplicate_state_callback<T: DriverConnectorState>(
     connector: *mut bindings::drm_connector
 ) -> *mut bindings::drm_connector_state
-- 
2.46.1