[RFC v3 15/33] 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>

---

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

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 rust/kernel/drm/kms/crtc.rs | 167 +++++++++++++++++++++++++++++++++++-
 1 file changed, 166 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/kms/crtc.rs b/rust/kernel/drm/kms/crtc.rs
index 9950b09754072..bcdd452ff7b10 100644
--- a/rust/kernel/drm/kms/crtc.rs
+++ b/rust/kernel/drm/kms/crtc.rs
@@ -4,7 +4,9 @@
 //!
 //! C header: [`include/drm/drm_crtc.h`](srctree/include/drm/drm_crtc.h)
 
-use super::{plane::*, KmsDriver, ModeObject, StaticModeObject, UnregisteredKmsDevice};
+use super::{
+    plane::*, KmsDriver, ModeObject, ModeObjectVtable, StaticModeObject, UnregisteredKmsDevice,
+};
 use crate::{
     alloc::KBox,
     bindings,
@@ -185,6 +187,25 @@ fn raw_mode_obj(&self) -> *mut bindings::drm_mode_object {
 // SAFETY: CRTCs are non-refcounted modesetting objects
 unsafe impl<T: DriverCrtc> StaticModeObject for Crtc<T> {}
 
+// SAFETY: `funcs` is initialized when the crtc is allocated
+unsafe impl<T: DriverCrtc> ModeObjectVtable for Crtc<T> {
+    type Vtable = bindings::drm_crtc_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        // SAFETY: `as_raw()` always returns a valid pointer to a CRTC
+        unsafe { *self.as_raw() }.funcs
+    }
+}
+
+impl<T: DriverCrtc> Crtc<T> {
+    super::impl_from_opaque_mode_obj! {
+        fn <'a, D>(&'a OpaqueCrtc<D>) -> &'a Self;
+        use
+            T as DriverCrtc,
+            D as KmsDriver
+    }
+}
+
 /// A [`Crtc`] that has not yet been registered with userspace.
 ///
 /// KMS registration is single-threaded, so this object is not thread-safe.
@@ -361,6 +382,86 @@ fn mask(&self) -> u32 {
 }
 impl<T: AsRawCrtc> RawCrtc for T {}
 
+/// 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> {}
+
+// SAFETY:
+// - Via our type variants our data layout is identical to `drm_crtc`
+// - Since we don't expose `OpaqueCrtc` to users before it has been initialized, this and our data
+//   layout ensure that `as_raw()` always returns a valid pointer to a `drm_crtc`.
+unsafe impl<T: KmsDriver> AsRawCrtc for OpaqueCrtc<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() }
+    }
+}
+
+// SAFETY: We only expose this object to users directly after KmsDriver::create_objects has been
+// called.
+unsafe impl<T: KmsDriver> ModesettableCrtc for OpaqueCrtc<T> {
+    type State = OpaqueCrtcState<T>;
+}
+
+// SAFETY: We don't expose OpaqueCrtc<T> to users before `base` is initialized in Crtc::<T>::new(),
+// so `raw_mode_obj` always returns a valid pointer to a bindings::drm_mode_object.
+unsafe 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> {}
+
+// SAFETY: `funcs` is initialized when the CRTC is allocated
+unsafe impl<T: KmsDriver> ModeObjectVtable for OpaqueCrtc<T> {
+    type Vtable = bindings::drm_crtc_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        // SAFETY: `as_raw()` always returns a valid pointer to a crtc
+        unsafe { (*self.as_raw()).funcs }
+    }
+}
+
 unsafe impl Zeroable for bindings::drm_crtc_state {}
 
 impl<T: DriverCrtcState> Sealed for CrtcState<T> {}
@@ -429,6 +530,26 @@ fn deref_mut(&mut self) -> &mut Self::Target {
     }
 }
 
+// SAFETY: Shares the safety guarantee of Crtc<T>'s ModeObjectVtable impl
+unsafe impl<T: DriverCrtcState> ModeObjectVtable for CrtcState<T> {
+    type Vtable = bindings::drm_crtc_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        self.crtc().vtable()
+    }
+}
+
+impl<T: DriverCrtcState> CrtcState<T> {
+    super::impl_from_opaque_mode_obj! {
+        fn <'a, D, C>(&'a OpaqueCrtcState<D>) -> &'a Self
+        where
+            T: DriverCrtcState<Crtc = C>;
+        use
+            C as DriverCrtc,
+            D as KmsDriver
+    }
+}
+
 /// A trait implemented by any type which can produce a reference to a [`struct drm_crtc_state`].
 ///
 /// This is implemented internally by DRM.
@@ -502,6 +623,50 @@ 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.
+///
+/// # 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()) }
+    }
+}
+
+// SAFETY: Shares the safety guarantees of OpaqueCrtc<T>'s ModeObjectVtable impl
+unsafe impl<T: KmsDriver> ModeObjectVtable for OpaqueCrtcState<T> {
+    type Vtable = bindings::drm_crtc_funcs;
+
+    fn vtable(&self) -> *const Self::Vtable {
+        self.crtc().vtable()
+    }
+}
+
 unsafe extern "C" fn crtc_destroy_callback<T: DriverCrtc>(crtc: *mut bindings::drm_crtc) {
     // SAFETY: DRM guarantees that `crtc` points to a valid initialized `drm_crtc`.
     unsafe { bindings::drm_crtc_cleanup(crtc) };
-- 
2.48.1