[RFC v3 17/33] rust: drm/kms: Add OpaqueEncoder

[Lyude Paul <lyude@redhat.com>]

Same thing as OpaquePlane, but for encoders now.

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

---

V3:
* Add safety comment to ModeObject implementation
* Add safety comments for AsRawEncoder
* Implement try_from_opaque() and from_opaque() using a macro

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 rust/kernel/drm/kms/encoder.rs | 91 +++++++++++++++++++++++++++++++++-
 1 file changed, 90 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/kms/encoder.rs b/rust/kernel/drm/kms/encoder.rs
index 2e4e88055c890..9ae2ff8eb5d50 100644
--- a/rust/kernel/drm/kms/encoder.rs
+++ b/rust/kernel/drm/kms/encoder.rs
@@ -4,7 +4,7 @@
 //!
 //! C header: [`include/drm/drm_encoder.h`](srctree/include/drm/drm_encoder.h)
 
-use super::{KmsDriver, ModeObject, StaticModeObject, UnregisteredKmsDevice};
+use super::{KmsDriver, ModeObject, ModeObjectVtable, StaticModeObject, UnregisteredKmsDevice};
 use crate::{
     alloc::KBox,
     drm::device::Device,
@@ -219,6 +219,25 @@ unsafe fn from_raw<'a>(ptr: *mut bindings::drm_encoder) -> &'a Self {
     }
 }
 
+// SAFETY: `funcs` is initialized when the encoder is allocated
+unsafe impl<T: DriverEncoder> ModeObjectVtable for Encoder<T> {
+    type Vtable = bindings::drm_encoder_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        // SAFETY: `as_raw()` always returns a valid pointer to an encoder
+        unsafe { *self.as_raw() }.funcs
+    }
+}
+
+impl<T: DriverEncoder> Encoder<T> {
+    super::impl_from_opaque_mode_obj! {
+        fn <'a, D>(&'a OpaqueEncoder<D>) -> &'a Self;
+        use
+            T as DriverEncoder,
+            D as KmsDriver
+    }
+}
+
 /// A [`Encoder`] that has not yet been registered with userspace.
 ///
 /// KMS registration is single-threaded, so this object is not thread-safe.
@@ -311,6 +330,76 @@ 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.
+///
+/// # 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> {}
+
+// SAFETY: We don't expose OpaqueEncoder<T> to users before `base` is initialized in
+// OpaqueEncoder::new(), so `raw_mode_obj` always returns a valid poiner to a
+// bindings::drm_mode_object.
+unsafe 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> {}
+
+// SAFETY:
+// - Via our type variants our data layout is identical to  with `drm_encoder`
+// - Since we don't expose `Encoder` to users before it has been initialized, this and our data
+//   layout ensure that `as_raw()` always returns a valid pointer to a `drm_encoder`.
+unsafe 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() }
+    }
+}
+
+// SAFETY: `funcs` is initialized when the encoder is allocated
+unsafe impl<T: KmsDriver> ModeObjectVtable for OpaqueEncoder<T> {
+    type Vtable = bindings::drm_encoder_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        // SAFETY: `as_raw()` always returns a valid pointer to an encoder
+        unsafe { *self.as_raw() }.funcs
+    }
+}
+
 unsafe extern "C" fn encoder_destroy_callback<T: DriverEncoder>(
     encoder: *mut bindings::drm_encoder,
 ) {
-- 
2.48.1