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.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/hrtimer.rs     | 28 +++++++++++++++++++++++++++-
 rust/kernel/hrtimer/arc.rs |  4 +---
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
index 6427b0450c694105190c8cddea0c768ab195aca2..eeed2afd501b64b94d57cc658616659e28785078 100644
--- a/rust/kernel/hrtimer.rs
+++ b/rust/kernel/hrtimer.rs
@@ -176,7 +176,7 @@ pub trait TimerCallback {
     type CallbackTargetParameter<'a>;
 
     /// Called by the timer logic when the timer fires.
-    fn run(this: Self::CallbackTargetParameter<'_>)
+    fn run(this: Self::CallbackTargetParameter<'_>) -> TimerRestart
     where
         Self: Sized;
 }
@@ -270,6 +270,32 @@ unsafe fn start(self_ptr: *const Self, expires: Ktime) {
     }
 }
 
+/// Restart policy for timers.
+pub enum TimerRestart {
+    /// Timer should not be restarted.
+    NoRestart,
+    /// Timer should be restarted.
+    Restart,
+}
+
+impl From<u32> for TimerRestart {
+    fn from(value: bindings::hrtimer_restart) -> Self {
+        match value {
+            0 => Self::NoRestart,
+            _ => Self::Restart,
+        }
+    }
+}
+
+impl From<TimerRestart> for bindings::hrtimer_restart {
+    fn from(value: TimerRestart) -> Self {
+        match value {
+            TimerRestart::NoRestart => bindings::hrtimer_restart_HRTIMER_NORESTART,
+            TimerRestart::Restart => bindings::hrtimer_restart_HRTIMER_RESTART,
+        }
+    }
+}
+
 /// Use to implement the [`HasTimer<T>`] trait.
 ///
 /// See [`module`] documentation for an example.
diff --git a/rust/kernel/hrtimer/arc.rs b/rust/kernel/hrtimer/arc.rs
index 881de053ecad866a26e46a0123ec2bf38511c2bc..c6283bd0dbb10dbc733c3f4092f107db2f3c5c5f 100644
--- a/rust/kernel/hrtimer/arc.rs
+++ b/rust/kernel/hrtimer/arc.rs
@@ -82,8 +82,6 @@ impl<U> RawTimerCallback for Arc<U>
         // timer. This `U` is contained in an `Arc`.
         let receiver = unsafe { ArcBorrow::from_raw(data_ptr) };
 
-        U::run(receiver);
-
-        bindings::hrtimer_restart_HRTIMER_NORESTART
+        U::run(receiver).into()
     }
 }

-- 
2.46.0

Hi Andreas,

kernel test robot noticed the following build errors:

[auto build test ERROR on 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b]

url:    https://github.com/intel-lab-lkp/linux/commits/Andreas-Hindborg/rust-time-Add-Ktime-from_ns/20241017-211351
base:   8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
patch link:    https://lore.kernel.org/r/20241017-hrtimer-v3-v6-12-rc2-v3-5-59a75cbb44da%40kernel.org
patch subject: [PATCH v3 05/13] rust: hrtimer: allow timer restart from timer handler
config: um-randconfig-002-20241020 (https://download.01.org/0day-ci/archive/20241021/202410210020.W6cyMg2D-lkp@intel.com/config)
compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project bfe84f7085d82d06d61c632a7bad1e692fd159e4)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241021/202410210020.W6cyMg2D-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202410210020.W6cyMg2D-lkp@intel.com/

All errors (new ones prefixed by >>):

>> error[E0053]: method `from` has an incompatible type for trait
   --> rust/kernel/hrtimer.rs:282:20
   |
   282 |     fn from(value: bindings::hrtimer_restart) -> Self {
   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^
   |                    |
   |                    expected `u32`, found `i32`
   |                    help: change the parameter type to match the trait: `u32`
   |
   = note: expected signature `fn(u32) -> TimerRestart`
   found signature `fn(i32) -> TimerRestart`

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki