rust: hrtimer: allow timer restart from timer handler

This patch allows timer handlers to report that they want a timer to be
restarted after the timer handler has finished executing.

Also update the `hrtimer` documentation to showcase the new feature.

Acked-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250224-hrtimer-v3-v6-12-rc2-v9-4-5bd3bf0ce6cc@kernel.org

Author: Andreas Hindborg

rust/kernel/time/hrtimer.rs

@@ -207,7 +207,7 @@ pub trait HrTimerCallback {
     type Pointer<'a>: RawHrTimerCallback;
 
     /// Called by the timer logic when the timer fires.
-    fn run(this: <Self::Pointer<'_> as RawHrTimerCallback>::CallbackTarget<'_>)
+    fn run(this: <Self::Pointer<'_> as RawHrTimerCallback>::CallbackTarget<'_>) -> HrTimerRestart
     where
         Self: Sized;
 }
@@ -313,6 +313,23 @@ pub unsafe trait HasHrTimer<T> {
     }
 }
 
+/// Restart policy for timers.
+pub enum HrTimerRestart {
+    /// Timer should not be restarted.
+    NoRestart,
+    /// Timer should be restarted.
+    Restart,
+}
+
+impl HrTimerRestart {
+    fn into_c(self) -> bindings::hrtimer_restart {
+        match self {
+            HrTimerRestart::NoRestart => bindings::hrtimer_restart_HRTIMER_NORESTART,
+            HrTimerRestart::Restart => bindings::hrtimer_restart_HRTIMER_RESTART,
+        }
+    }
+}
+
 /// Use to implement the [`HasHrTimer<T>`] trait.
 ///
 /// See [`module`] documentation for an example.

rust/kernel/time/hrtimer/arc.rs

@@ -87,8 +87,6 @@ where
         // timer. This `T` is contained in an `Arc`.
         let receiver = unsafe { ArcBorrow::from_raw(data_ptr) };
 
-        T::run(receiver);
-
-        bindings::hrtimer_restart_HRTIMER_NORESTART
+        T::run(receiver).into_c()
     }
 }