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     | 50 ++++++++++++++++++++++++++++++++------
 rust/kernel/hrtimer/arc.rs |  4 +--
 2 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
index fd1520ba9fba..d6c3fa89f77e 100644
--- a/rust/kernel/hrtimer.rs
+++ b/rust/kernel/hrtimer.rs
@@ -9,7 +9,7 @@
 //!
 //! ```
 //! use kernel::{
-//!     hrtimer::{Timer, TimerCallback, TimerPointer},
+//!     hrtimer::{Timer, TimerCallback, TimerPointer, TimerRestart},
 //!     impl_has_timer, new_condvar, new_mutex,
 //!     prelude::*,
 //!     sync::{Arc, CondVar, Mutex},
@@ -21,7 +21,7 @@
 //!     #[pin]
 //!     timer: Timer<Self>,
 //!     #[pin]
-//!     flag: Mutex<bool>,
+//!     flag: Mutex<u64>,
 //!     #[pin]
 //!     cond: CondVar,
 //! }
@@ -30,7 +30,7 @@
 //!     fn new() -> impl PinInit<Self, kernel::error::Error> {
 //!         try_pin_init!(Self {
 //!             timer <- Timer::new(),
-//!             flag <- new_mutex!(false),
+//!             flag <- new_mutex!(0),
 //!             cond <- new_condvar!(),
 //!         })
 //!     }
@@ -39,10 +39,18 @@
 //! impl TimerCallback for ArcIntrusiveTimer {
 //!     type CallbackTarget<'a> = Arc<Self>;
 //!
-//!     fn run(this: Self::CallbackTarget<'_>) {
+//!     fn run(this: Self::CallbackTarget<'_>) -> TimerRestart {
 //!         pr_info!("Timer called\n");
-//!         *this.flag.lock() = true;
+//!         let mut guard = this.flag.lock();
+//!         *guard += 1;
 //!         this.cond.notify_all();
+//!         if *guard == 5 {
+//!             TimerRestart::NoRestart
+//!         }
+//!         else {
+//!             TimerRestart::Restart
+//!
+//!         }
 //!     }
 //! }
 //!
@@ -55,11 +63,11 @@
 //! let _handle = has_timer.clone().schedule(Ktime::from_ns(200_000_000));
 //! let mut guard = has_timer.flag.lock();
 //!
-//! while !*guard {
+//! while *guard != 5 {
 //!     has_timer.cond.wait(&mut guard);
 //! }
 //!
-//! pr_info!("Flag raised\n");
+//! pr_info!("Counted to 5\n");
 //! # Ok::<(), kernel::error::Error>(())
 //! ```
 
@@ -202,7 +210,7 @@ pub trait TimerCallback {
     type CallbackTarget<'a>: RawTimerCallback;
 
     /// Called by the timer logic when the timer fires.
-    fn run(this: Self::CallbackTarget<'_>)
+    fn run(this: Self::CallbackTarget<'_>) -> TimerRestart
     where
         Self: Sized;
 }
@@ -296,6 +304,32 @@ unsafe fn schedule(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 80f6c20f95a9..fb8a40484add 100644
--- a/rust/kernel/hrtimer/arc.rs
+++ b/rust/kernel/hrtimer/arc.rs
@@ -80,8 +80,6 @@ impl<U> RawTimerCallback for Arc<U>
         // timer. This `U` is contained in an `Arc`.
         let receiver = unsafe { Arc::clone_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 98f7e32f20d28ec452afb208f9cffc08448a2652]

url:    https://github.com/intel-lab-lkp/linux/commits/Andreas-Hindborg/rust-time-Add-Ktime-from_ns/20240918-063405
base:   98f7e32f20d28ec452afb208f9cffc08448a2652
patch link:    https://lore.kernel.org/r/20240917222739.1298275-7-a.hindborg%40kernel.org
patch subject: [PATCH v2 06/14] rust: hrtimer: allow timer restart from timer handler
config: riscv-randconfig-002-20240920 (https://download.01.org/0day-ci/archive/20240920/202409202251.Sfvd2aUn-lkp@intel.com/config)
compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project 8663a75fa2f31299ab8d1d90288d9df92aadee88)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240920/202409202251.Sfvd2aUn-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/202409202251.Sfvd2aUn-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from arch/riscv/kernel/asm-offsets.c:10:
   In file included from include/linux/mm.h:2232:
   include/linux/vmstat.h:517:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
   517 |         return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
   |                               ~~~~~~~~~~~ ^ ~~~
   1 warning generated.
   clang diag: include/linux/vmstat.h:517:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
   clang diag: include/linux/vmstat.h:517:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
   clang diag: include/linux/vmstat.h:517:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
>> error[E0053]: method `from` has an incompatible type for trait
   --> rust/kernel/hrtimer.rs:316:20
   |
   316 |     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