rust: time: Make HasHrTimer generic over HrTimerMode

Add a `TimerMode` associated type to the `HasHrTimer` trait to
represent the operational mode of the timer, such as absolute or
relative expiration. This new type must implement the `HrTimerMode`
trait, which defines how expiration values are interpreted.

Update the `start()` method to accept an `expires` parameter of type
`<Self::TimerMode as HrTimerMode>::Expires` instead of the fixed `Ktime`.
This enables different timer modes to provide strongly typed expiration
values, such as `Instant<C>` or `Delta`.

The `impl_has_hr_timer` macro is also extended to allow specifying the
`HrTimerMode`. In the following example, it guarantees that the
`start()` method for `Foo` only accepts `Instant<Monotonic>`. Using a
`Delta` or an `Instant` with a different clock source will result in a
compile-time error:

struct Foo {
    #[pin]
    timer: HrTimer<Self>,
}

impl_has_hr_timer! {
    impl HasHrTimer<Self> for Foo {
        mode : AbsoluteMode<Monotonic>,
        field : self.timer
    }
}

This design eliminates runtime mismatches between expires types and
clock sources, and enables stronger type-level guarantees throughout
hrtimer.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250610132823.3457263-5-fujita.tomonori@gmail.com
[ changed conversion method names to `as_*` - Andreas ]
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/rust/kernel/time/hrtimer/tbox.rs b/rust/kernel/time/hrtimer/tbox.rs
index 29526a5da203..ec08303315f2 100644
--- a/rust/kernel/time/hrtimer/tbox.rs
+++ b/rust/kernel/time/hrtimer/tbox.rs
@@ -4,8 +4,8 @@ use super::HasHrTimer;
 use super::HrTimer;
 use super::HrTimerCallback;
 use super::HrTimerHandle;
+use super::HrTimerMode;
 use super::HrTimerPointer;
-use super::Ktime;
 use super::RawHrTimerCallback;
 use crate::prelude::*;
 use core::ptr::NonNull;
@@ -64,9 +64,13 @@ where
     T: for<'a> HrTimerCallback<Pointer<'a> = Pin<Box<T, A>>>,
     A: crate::alloc::Allocator,
 {
+    type TimerMode = <T as HasHrTimer<T>>::TimerMode;
     type TimerHandle = BoxHrTimerHandle<T, A>;
 
-    fn start(self, expires: Ktime) -> Self::TimerHandle {
+    fn start(
+        self,
+        expires: <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Expires,
+    ) -> Self::TimerHandle {
         // SAFETY:
         //  - We will not move out of this box during timer callback (we pass an
         //    immutable reference to the callback).