[PATCH v2 5/8] rust: drm: add DRM driver registration

[Danilo Krummrich <dakr@redhat.com>]

Implement the DRM driver `Registration`.

The `Registration` structure is responsible to register and unregister a
DRM driver. It makes use of the `Devres` container in order to allow the
`Registration` to be owned by devres, such that it is automatically
dropped (and the DRM driver unregistered) once the parent device is
unbound.

Co-developed-by: Asahi Lina <lina@asahilina.net>
Signed-off-by: Asahi Lina <lina@asahilina.net>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
---
 rust/kernel/drm/drv.rs | 57 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 56 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/drv.rs b/rust/kernel/drm/drv.rs
index cd594a32f9e4..ebb79a8c90ee 100644
--- a/rust/kernel/drm/drv.rs
+++ b/rust/kernel/drm/drv.rs
@@ -4,7 +4,16 @@
 //!
 //! C header: [`include/linux/drm/drm_drv.h`](srctree/include/linux/drm/drm_drv.h)
 
-use crate::{bindings, drm, private::Sealed, str::CStr, types::ForeignOwnable};
+use crate::{
+    alloc::flags::*,
+    bindings,
+    devres::Devres,
+    drm,
+    error::{Error, Result},
+    private::Sealed,
+    str::CStr,
+    types::{ARef, ForeignOwnable},
+};
 use macros::vtable;
 
 /// Driver use the GEM memory manager. This should be set for all modern drivers.
@@ -139,3 +148,49 @@ pub trait Driver {
     /// IOCTL list. See `kernel::drm::ioctl::declare_drm_ioctls!{}`.
     const IOCTLS: &'static [drm::ioctl::DrmIoctlDescriptor];
 }
+
+/// The registration type of a `drm::device::Device`.
+///
+/// Once the `Registration` structure is dropped, the device is unregistered.
+pub struct Registration<T: Driver>(ARef<drm::device::Device<T>>);
+
+impl<T: Driver> Registration<T> {
+    /// Creates a new [`Registration`] and registers it.
+    pub fn new(drm: ARef<drm::device::Device<T>>, flags: usize) -> Result<Self> {
+        // SAFETY: Safe by the invariants of `drm::device::Device`.
+        let ret = unsafe { bindings::drm_dev_register(drm.as_raw(), flags as u64) };
+        if ret < 0 {
+            return Err(Error::from_errno(ret));
+        }
+
+        Ok(Self(drm))
+    }
+
+    /// Same as [`Registration::new`}, but transfers ownership of the [`Registration`] to `Devres`.
+    pub fn new_foreign_owned(drm: ARef<drm::device::Device<T>>, flags: usize) -> Result {
+        let reg = Registration::<T>::new(drm.clone(), flags)?;
+
+        Devres::new_foreign_owned(drm.as_ref(), reg, GFP_KERNEL)
+    }
+
+    /// Returns a reference to the `Device` instance for this registration.
+    pub fn device(&self) -> &drm::device::Device<T> {
+        &self.0
+    }
+}
+
+// SAFETY: `Registration` doesn't offer any methods or access to fields when shared between
+// threads, hence it's safe to share it.
+unsafe impl<T: Driver> Sync for Registration<T> {}
+
+// SAFETY: Registration with and unregistration from the DRM subsystem can happen from any thread.
+unsafe impl<T: Driver> Send for Registration<T> {}
+
+impl<T: Driver> Drop for Registration<T> {
+    /// Removes the registration from the kernel if it has completed successfully before.
+    fn drop(&mut self) {
+        // SAFETY: Safe by the invariant of `ARef<drm::device::Device<T>>`. The existance of this
+        // `Registration` also guarantees the this `drm::device::Device` is actually registered.
+        unsafe { bindings::drm_dev_unregister(self.0.as_raw()) };
+    }
+}
-- 
2.45.1