[PATCH v3 07/13] rust: hrtimer: implement `UnsafeTimerPointer` for `Pin<&T>`

[Andreas Hindborg <a.hindborg@kernel.org>]

Allow pinned references to structs that contain a `Timer` node to be
scheduled with the `hrtimer` subsystem.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/hrtimer.rs     |  1 +
 rust/kernel/hrtimer/pin.rs | 97 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)

diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
index e97d7b8ec63ce6c9ac3fe9522192a28fba78b8ba..ceedf330a803ec2db7ff6c25713ae48e2fd1f4ca 100644
--- a/rust/kernel/hrtimer.rs
+++ b/rust/kernel/hrtimer.rs
@@ -362,3 +362,4 @@ unsafe fn raw_get_timer(ptr: *const Self) ->
 }
 
 mod arc;
+mod pin;
diff --git a/rust/kernel/hrtimer/pin.rs b/rust/kernel/hrtimer/pin.rs
new file mode 100644
index 0000000000000000000000000000000000000000..a2c1dbd5e48b668cc3dc540c5fd5514f5331d968
--- /dev/null
+++ b/rust/kernel/hrtimer/pin.rs
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::HasTimer;
+use super::RawTimerCallback;
+use super::Timer;
+use super::TimerCallback;
+use super::TimerHandle;
+use super::UnsafeTimerPointer;
+use crate::time::Ktime;
+use core::pin::Pin;
+
+/// A handle for a `Pin<&HasTimer>`. When the handle exists, the timer might be
+/// running.
+pub struct PinTimerHandle<'a, U>
+where
+    U: HasTimer<U>,
+{
+    pub(crate) inner: Pin<&'a U>,
+}
+
+// SAFETY: We cancel the timer when the handle is dropped. The implementation of
+// the `cancel` method will block if the timer handler is running.
+unsafe impl<'a, U> TimerHandle for PinTimerHandle<'a, U>
+where
+    U: HasTimer<U>,
+{
+    fn cancel(&mut self) -> bool {
+        let self_ptr = self.inner.get_ref() as *const U;
+
+        // SAFETY: As we got `self_ptr` from a reference above, it must point to
+        // a valid `U`.
+        let timer_ptr = unsafe { <U as HasTimer<U>>::raw_get_timer(self_ptr) };
+
+        // SAFETY: As `timer_ptr` is derived from a reference, it must point to
+        // a valid and initialized `Timer`.
+        unsafe { Timer::<U>::raw_cancel(timer_ptr) }
+    }
+}
+
+impl<'a, U> Drop for PinTimerHandle<'a, U>
+where
+    U: HasTimer<U>,
+{
+    fn drop(&mut self) {
+        self.cancel();
+    }
+}
+
+// SAFETY: We capture the lifetime of `Self` when we create a `PinTimerHandle`,
+// so `Self` will outlive the handle.
+unsafe impl<'a, U> UnsafeTimerPointer for Pin<&'a U>
+where
+    U: Send + Sync,
+    U: HasTimer<U>,
+    U: TimerCallback<CallbackTarget<'a> = Self>,
+{
+    type TimerHandle = PinTimerHandle<'a, U>;
+
+    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle {
+        use core::ops::Deref;
+
+        // Cast to pointer
+        let self_ptr = self.deref() as *const U;
+
+        // SAFETY: As we derive `self_ptr` from a reference above, it must point
+        // to a valid `U`.
+        unsafe { U::start(self_ptr, expires) };
+
+        PinTimerHandle { inner: self }
+    }
+}
+
+impl<'a, U> RawTimerCallback for Pin<&'a U>
+where
+    U: HasTimer<U>,
+    U: TimerCallback<CallbackTarget<'a> = Self>,
+    U: TimerCallback<CallbackTargetParameter<'a> = Self>,
+{
+    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
+        // `Timer` is `repr(C)`
+        let timer_ptr = ptr as *mut Timer<U>;
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `Timer<U>` contained in an `U`.
+        let receiver_ptr = unsafe { U::timer_container_of(timer_ptr) };
+
+        // SAFETY: By the safety requirement of this function, `timer_ptr`
+        // points to a `Timer<U>` contained in an `U`.
+        let receiver_ref = unsafe { &*receiver_ptr };
+
+        // SAFETY: `receiver_ref` only exists as pinned, so it is safe to pin it
+        // here.
+        let receiver_pin = unsafe { Pin::new_unchecked(receiver_ref) };
+
+        U::run(receiver_pin).into()
+    }
+}

-- 
2.46.0