Merge tag 'rust-timekeeping-for-v6.17' of https://github.com/Rust-for-Linux/linux into rust-next

Pull timekeeping updates from Andreas Hindborg:

 - Make 'Instant' generic over clock source. This allows the compiler to
   assert that arithmetic expressions involving the 'Instant' use
   'Instants' based on the same clock source.

 - Make 'HrTimer' generic over the timer mode. 'HrTimer' timers take a
   'Duration' or an 'Instant' when setting the expiry time, depending on
   the timer mode. With this change, the compiler can check the type
   matches the timer mode.

 - Add an abstraction for 'fsleep'. 'fsleep' is a flexible sleep
   function that will select an appropriate sleep method depending on
   the requested sleep time.

 - Avoid 64-bit divisions on 32-bit hardware when calculating
   timestamps.

 - Seal the 'HrTimerMode' trait. This prevents users of the
   'HrTimerMode' from implementing the trait on their own types.

* tag 'rust-timekeeping-for-v6.17' of https://github.com/Rust-for-Linux/linux:
  rust: time: Add wrapper for fsleep() function
  rust: time: Seal the HrTimerMode trait
  rust: time: Remove Ktime in hrtimer
  rust: time: Make HasHrTimer generic over HrTimerMode
  rust: time: Add HrTimerExpires trait
  rust: time: Replace HrTimerMode enum with trait-based mode types
  rust: time: Add ktime_get() to ClockSource trait
  rust: time: Make Instant generic over ClockSource
  rust: time: Replace ClockId enum with ClockSource trait
  rust: time: Avoid 64-bit integer division on 32-bit architectures

9 files changed, 466 insertions, 186 deletions

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index d3867d09e356..0683fffdbde2 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -41,6 +41,7 @@
 #include "spinlock.c"
 #include "sync.c"
 #include "task.c"
+#include "time.c"
 #include "uaccess.c"
 #include "vmalloc.c"
 #include "wait.c"
diff --git a/rust/helpers/time.c b/rust/helpers/time.c
new file mode 100644
index 000000000000..a318e9fa4408
--- /dev/null
+++ b/rust/helpers/time.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/delay.h>
+#include <linux/ktime.h>
+#include <linux/timekeeping.h>
+
+void rust_helper_fsleep(unsigned long usecs)
+{
+	fsleep(usecs);
+}
+
+ktime_t rust_helper_ktime_get_real(void)
+{
+	return ktime_get_real();
+}
+
+ktime_t rust_helper_ktime_get_boottime(void)
+{
+	return ktime_get_boottime();
+}
+
+ktime_t rust_helper_ktime_get_clocktai(void)
+{
+	return ktime_get_clocktai();
+}
+
+s64 rust_helper_ktime_to_us(const ktime_t kt)
+{
+	return ktime_to_us(kt);
+}
+
+s64 rust_helper_ktime_to_ms(const ktime_t kt)
+{
+	return ktime_to_ms(kt);
+}
diff --git a/rust/kernel/time.rs b/rust/kernel/time.rs
index a8089a98da9e..64c8dcf548d6 100644
--- a/rust/kernel/time.rs
+++ b/rust/kernel/time.rs
@@ -24,6 +24,9 @@
 //! C header: [`include/linux/jiffies.h`](srctree/include/linux/jiffies.h).
 //! C header: [`include/linux/ktime.h`](srctree/include/linux/ktime.h).
 
+use core::marker::PhantomData;
+
+pub mod delay;
 pub mod hrtimer;
 
 /// The number of nanoseconds per microsecond.
@@ -49,26 +52,141 @@ pub fn msecs_to_jiffies(msecs: Msecs) -> Jiffies {
     unsafe { bindings::__msecs_to_jiffies(msecs) }
 }
 
+/// Trait for clock sources.
+///
+/// Selection of the clock source depends on the use case. In some cases the usage of a
+/// particular clock is mandatory, e.g. in network protocols, filesystems. In other
+/// cases the user of the clock has to decide which clock is best suited for the
+/// purpose. In most scenarios clock [`Monotonic`] is the best choice as it
+/// provides a accurate monotonic notion of time (leap second smearing ignored).
+pub trait ClockSource {
+    /// The kernel clock ID associated with this clock source.
+    ///
+    /// This constant corresponds to the C side `clockid_t` value.
+    const ID: bindings::clockid_t;
+
+    /// Get the current time from the clock source.
+    ///
+    /// The function must return a value in the range from 0 to `KTIME_MAX`.
+    fn ktime_get() -> bindings::ktime_t;
+}
+
+/// A monotonically increasing clock.
+///
+/// A nonsettable system-wide clock that represents monotonic time since as
+/// described by POSIX, "some unspecified point in the past". On Linux, that
+/// point corresponds to the number of seconds that the system has been
+/// running since it was booted.
+///
+/// The CLOCK_MONOTONIC clock is not affected by discontinuous jumps in the
+/// CLOCK_REAL (e.g., if the system administrator manually changes the
+/// clock), but is affected by frequency adjustments. This clock does not
+/// count time that the system is suspended.
+pub struct Monotonic;
+
+impl ClockSource for Monotonic {
+    const ID: bindings::clockid_t = bindings::CLOCK_MONOTONIC as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get()` outside of NMI context.
+        unsafe { bindings::ktime_get() }
+    }
+}
+
+/// A settable system-wide clock that measures real (i.e., wall-clock) time.
+///
+/// Setting this clock requires appropriate privileges. This clock is
+/// affected by discontinuous jumps in the system time (e.g., if the system
+/// administrator manually changes the clock), and by frequency adjustments
+/// performed by NTP and similar applications via adjtime(3), adjtimex(2),
+/// clock_adjtime(2), and ntp_adjtime(3). This clock normally counts the
+/// number of seconds since 1970-01-01 00:00:00 Coordinated Universal Time
+/// (UTC) except that it ignores leap seconds; near a leap second it may be
+/// adjusted by leap second smearing to stay roughly in sync with UTC. Leap
+/// second smearing applies frequency adjustments to the clock to speed up
+/// or slow down the clock to account for the leap second without
+/// discontinuities in the clock. If leap second smearing is not applied,
+/// the clock will experience discontinuity around leap second adjustment.
+pub struct RealTime;
+
+impl ClockSource for RealTime {
+    const ID: bindings::clockid_t = bindings::CLOCK_REALTIME as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get_real()` outside of NMI context.
+        unsafe { bindings::ktime_get_real() }
+    }
+}
+
+/// A monotonic that ticks while system is suspended.
+///
+/// A nonsettable system-wide clock that is identical to CLOCK_MONOTONIC,
+/// except that it also includes any time that the system is suspended. This
+/// allows applications to get a suspend-aware monotonic clock without
+/// having to deal with the complications of CLOCK_REALTIME, which may have
+/// discontinuities if the time is changed using settimeofday(2) or similar.
+pub struct BootTime;
+
+impl ClockSource for BootTime {
+    const ID: bindings::clockid_t = bindings::CLOCK_BOOTTIME as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get_boottime()` outside of NMI context.
+        unsafe { bindings::ktime_get_boottime() }
+    }
+}
+
+/// International Atomic Time.
+///
+/// A system-wide clock derived from wall-clock time but counting leap seconds.
+///
+/// This clock is coupled to CLOCK_REALTIME and will be set when CLOCK_REALTIME is
+/// set, or when the offset to CLOCK_REALTIME is changed via adjtimex(2). This
+/// usually happens during boot and **should** not happen during normal operations.
+/// However, if NTP or another application adjusts CLOCK_REALTIME by leap second
+/// smearing, this clock will not be precise during leap second smearing.
+///
+/// The acronym TAI refers to International Atomic Time.
+pub struct Tai;
+
+impl ClockSource for Tai {
+    const ID: bindings::clockid_t = bindings::CLOCK_TAI as bindings::clockid_t;
+
+    fn ktime_get() -> bindings::ktime_t {
+        // SAFETY: It is always safe to call `ktime_get_tai()` outside of NMI context.
+        unsafe { bindings::ktime_get_clocktai() }
+    }
+}
+
 /// A specific point in time.
 ///
 /// # Invariants
 ///
 /// The `inner` value is in the range from 0 to `KTIME_MAX`.
 #[repr(transparent)]
-#[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord)]
-pub struct Instant {
+#[derive(PartialEq, PartialOrd, Eq, Ord)]
+pub struct Instant<C: ClockSource> {
     inner: bindings::ktime_t,
+    _c: PhantomData<C>,
+}
+
+impl<C: ClockSource> Clone for Instant<C> {
+    fn clone(&self) -> Self {
+        *self
+    }
 }
 
-impl Instant {
-    /// Get the current time using `CLOCK_MONOTONIC`.
+impl<C: ClockSource> Copy for Instant<C> {}
+
+impl<C: ClockSource> Instant<C> {
+    /// Get the current time from the clock source.
     #[inline]
     pub fn now() -> Self {
-        // INVARIANT: The `ktime_get()` function returns a value in the range
+        // INVARIANT: The `ClockSource::ktime_get()` function returns a value in the range
         // from 0 to `KTIME_MAX`.
         Self {
-            // SAFETY: It is always safe to call `ktime_get()` outside of NMI context.
-            inner: unsafe { bindings::ktime_get() },
+            inner: C::ktime_get(),
+            _c: PhantomData,
         }
     }
 
@@ -77,86 +195,25 @@ impl Instant {
     pub fn elapsed(&self) -> Delta {
         Self::now() - *self
     }
+
+    #[inline]
+    pub(crate) fn as_nanos(&self) -> i64 {
+        self.inner
+    }
 }
 
-impl core::ops::Sub for Instant {
+impl<C: ClockSource> core::ops::Sub for Instant<C> {
     type Output = Delta;
 
     // By the type invariant, it never overflows.
     #[inline]
-    fn sub(self, other: Instant) -> Delta {
+    fn sub(self, other: Instant<C>) -> Delta {
         Delta {
             nanos: self.inner - other.inner,
         }
     }
 }
 
-/// An identifier for a clock. Used when specifying clock sources.
-///
-///
-/// Selection of the clock depends on the use case. In some cases the usage of a
-/// particular clock is mandatory, e.g. in network protocols, filesystems.In other
-/// cases the user of the clock has to decide which clock is best suited for the
-/// purpose. In most scenarios clock [`ClockId::Monotonic`] is the best choice as it
-/// provides a accurate monotonic notion of time (leap second smearing ignored).
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
-#[repr(u32)]
-pub enum ClockId {
-    /// A settable system-wide clock that measures real (i.e., wall-clock) time.
-    ///
-    /// Setting this clock requires appropriate privileges. This clock is
-    /// affected by discontinuous jumps in the system time (e.g., if the system
-    /// administrator manually changes the clock), and by frequency adjustments
-    /// performed by NTP and similar applications via adjtime(3), adjtimex(2),
-    /// clock_adjtime(2), and ntp_adjtime(3). This clock normally counts the
-    /// number of seconds since 1970-01-01 00:00:00 Coordinated Universal Time
-    /// (UTC) except that it ignores leap seconds; near a leap second it may be
-    /// adjusted by leap second smearing to stay roughly in sync with UTC. Leap
-    /// second smearing applies frequency adjustments to the clock to speed up
-    /// or slow down the clock to account for the leap second without
-    /// discontinuities in the clock. If leap second smearing is not applied,
-    /// the clock will experience discontinuity around leap second adjustment.
-    RealTime = bindings::CLOCK_REALTIME,
-    /// A monotonically increasing clock.
-    ///
-    /// A nonsettable system-wide clock that represents monotonic time since—as
-    /// described by POSIX—"some unspecified point in the past". On Linux, that
-    /// point corresponds to the number of seconds that the system has been
-    /// running since it was booted.
-    ///
-    /// The CLOCK_MONOTONIC clock is not affected by discontinuous jumps in the
-    /// CLOCK_REAL (e.g., if the system administrator manually changes the
-    /// clock), but is affected by frequency adjustments. This clock does not
-    /// count time that the system is suspended.
-    Monotonic = bindings::CLOCK_MONOTONIC,
-    /// A monotonic that ticks while system is suspended.
-    ///
-    /// A nonsettable system-wide clock that is identical to CLOCK_MONOTONIC,
-    /// except that it also includes any time that the system is suspended. This
-    /// allows applications to get a suspend-aware monotonic clock without
-    /// having to deal with the complications of CLOCK_REALTIME, which may have
-    /// discontinuities if the time is changed using settimeofday(2) or similar.
-    BootTime = bindings::CLOCK_BOOTTIME,
-    /// International Atomic Time.
-    ///
-    /// A system-wide clock derived from wall-clock time but counting leap seconds.
-    ///
-    /// This clock is coupled to CLOCK_REALTIME and will be set when CLOCK_REALTIME is
-    /// set, or when the offset to CLOCK_REALTIME is changed via adjtimex(2). This
-    /// usually happens during boot and **should** not happen during normal operations.
-    /// However, if NTP or another application adjusts CLOCK_REALTIME by leap second
-    /// smearing, this clock will not be precise during leap second smearing.
-    ///
-    /// The acronym TAI refers to International Atomic Time.
-    TAI = bindings::CLOCK_TAI,
-}
-
-impl ClockId {
-    fn into_c(self) -> bindings::clockid_t {
-        self as bindings::clockid_t
-    }
-}
-
 /// A span of time.
 ///
 /// This struct represents a span of time, with its value stored as nanoseconds.
@@ -228,13 +285,31 @@ impl Delta {
     /// Return the smallest number of microseconds greater than or equal
     /// to the value in the [`Delta`].
     #[inline]
-    pub const fn as_micros_ceil(self) -> i64 {
-        self.as_nanos().saturating_add(NSEC_PER_USEC - 1) / NSEC_PER_USEC
+    pub fn as_micros_ceil(self) -> i64 {
+        #[cfg(CONFIG_64BIT)]
+        {
+            self.as_nanos().saturating_add(NSEC_PER_USEC - 1) / NSEC_PER_USEC
+        }
+
+        #[cfg(not(CONFIG_64BIT))]
+        // SAFETY: It is always safe to call `ktime_to_us()` with any value.
+        unsafe {
+            bindings::ktime_to_us(self.as_nanos().saturating_add(NSEC_PER_USEC - 1))
+        }
     }
 
     /// Return the number of milliseconds in the [`Delta`].
     #[inline]
-    pub const fn as_millis(self) -> i64 {
-        self.as_nanos() / NSEC_PER_MSEC
+    pub fn as_millis(self) -> i64 {
+        #[cfg(CONFIG_64BIT)]
+        {
+            self.as_nanos() / NSEC_PER_MSEC
+        }
+
+        #[cfg(not(CONFIG_64BIT))]
+        // SAFETY: It is always safe to call `ktime_to_ms()` with any value.
+        unsafe {
+            bindings::ktime_to_ms(self.as_nanos())
+        }
     }
 }
diff --git a/rust/kernel/time/delay.rs b/rust/kernel/time/delay.rs
new file mode 100644
index 000000000000..eb8838da62bc
--- /dev/null
+++ b/rust/kernel/time/delay.rs
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Delay and sleep primitives.
+//!
+//! This module contains the kernel APIs related to delay and sleep that
+//! have been ported or wrapped for usage by Rust code in the kernel.
+//!
+//! C header: [`include/linux/delay.h`](srctree/include/linux/delay.h).
+
+use super::Delta;
+use crate::prelude::*;
+
+/// Sleeps for a given duration at least.
+///
+/// Equivalent to the C side [`fsleep()`], flexible sleep function,
+/// which automatically chooses the best sleep method based on a duration.
+///
+/// `delta` must be within `[0, i32::MAX]` microseconds;
+/// otherwise, it is erroneous behavior. That is, it is considered a bug
+/// to call this function with an out-of-range value, in which case the function
+/// will sleep for at least the maximum value in the range and may warn
+/// in the future.
+///
+/// The behavior above differs from the C side [`fsleep()`] for which out-of-range
+/// values mean "infinite timeout" instead.
+///
+/// This function can only be used in a nonatomic context.
+///
+/// [`fsleep()`]: https://docs.kernel.org/timers/delay_sleep_functions.html#c.fsleep
+pub fn fsleep(delta: Delta) {
+    // The maximum value is set to `i32::MAX` microseconds to prevent integer
+    // overflow inside fsleep, which could lead to unintentional infinite sleep.
+    const MAX_DELTA: Delta = Delta::from_micros(i32::MAX as i64);
+
+    let delta = if (Delta::ZERO..=MAX_DELTA).contains(&delta) {
+        delta
+    } else {
+        // TODO: Add WARN_ONCE() when it's supported.
+        MAX_DELTA
+    };
+
+    // SAFETY: It is always safe to call `fsleep()` with any duration.
+    unsafe {
+        // Convert the duration to microseconds and round up to preserve
+        // the guarantee; `fsleep()` sleeps for at least the provided duration,
+        // but that it may sleep for longer under some circumstances.
+        bindings::fsleep(delta.as_micros_ceil() as c_ulong)
+    }
+}
diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
index 113463e64815..d6830b6bbee7 100644
--- a/rust/kernel/time/hrtimer.rs
+++ b/rust/kernel/time/hrtimer.rs
@@ -67,27 +67,11 @@
 //! A `restart` operation on a timer in the **stopped** state is equivalent to a
 //! `start` operation.
 
-use super::ClockId;
+use super::{ClockSource, Delta, Instant};
 use crate::{prelude::*, types::Opaque};
 use core::marker::PhantomData;
 use pin_init::PinInit;
 
-/// A Rust wrapper around a `ktime_t`.
-// NOTE: Ktime is going to be removed when hrtimer is converted to Instant/Delta.
-#[repr(transparent)]
-#[derive(Copy, Clone, PartialEq, PartialOrd, Eq, Ord)]
-pub struct Ktime {
-    inner: bindings::ktime_t,
-}
-
-impl Ktime {
-    /// Returns the number of nanoseconds.
-    #[inline]
-    pub fn to_ns(self) -> i64 {
-        self.inner
-    }
-}
-
 /// A timer backed by a C `struct hrtimer`.
 ///
 /// # Invariants
@@ -98,7 +82,6 @@ impl Ktime {
 pub struct HrTimer<T> {
     #[pin]
     timer: Opaque<bindings::hrtimer>,
-    mode: HrTimerMode,
     _t: PhantomData<T>,
 }
 
@@ -112,9 +95,10 @@ unsafe impl<T> Sync for HrTimer<T> {}
 
 impl<T> HrTimer<T> {
     /// Return an initializer for a new timer instance.
-    pub fn new(mode: HrTimerMode, clock: ClockId) -> impl PinInit<Self>
+    pub fn new() -> impl PinInit<Self>
     where
         T: HrTimerCallback,
+        T: HasHrTimer<T>,
     {
         pin_init!(Self {
             // INVARIANT: We initialize `timer` with `hrtimer_setup` below.
@@ -126,12 +110,11 @@ impl<T> HrTimer<T> {
                     bindings::hrtimer_setup(
                         place,
                         Some(T::Pointer::run),
-                        clock.into_c(),
-                        mode.into_c(),
+                        <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Clock::ID,
+                        <T as HasHrTimer<T>>::TimerMode::C_MODE,
                     );
                 }
             }),
-            mode: mode,
             _t: PhantomData,
         })
     }
@@ -193,6 +176,11 @@ impl<T> HrTimer<T> {
 /// exist. A timer can be manipulated through any of the handles, and a handle
 /// may represent a cancelled timer.
 pub trait HrTimerPointer: Sync + Sized {
+    /// The operational mode associated with this timer.
+    ///
+    /// This defines how the expiration value is interpreted.
+    type TimerMode: HrTimerMode;
+
     /// A handle representing a started or restarted timer.
     ///
     /// If the timer is running or if the timer callback is executing when the
@@ -205,7 +193,7 @@ pub trait HrTimerPointer: Sync + Sized {
 
     /// Start the timer with expiry after `expires` time units. If the timer was
     /// already running, it is restarted with the new expiry time.
-    fn start(self, expires: Ktime) -> Self::TimerHandle;
+    fn start(self, expires: <Self::TimerMode as HrTimerMode>::Expires) -> Self::TimerHandle;
 }
 
 /// Unsafe version of [`HrTimerPointer`] for situations where leaking the
@@ -220,6 +208,11 @@ pub trait HrTimerPointer: Sync + Sized {
 /// [`UnsafeHrTimerPointer`] outlives any associated [`HrTimerPointer::TimerHandle`]
 /// instances.
 pub unsafe trait UnsafeHrTimerPointer: Sync + Sized {
+    /// The operational mode associated with this timer.
+    ///
+    /// This defines how the expiration value is interpreted.
+    type TimerMode: HrTimerMode;
+
     /// A handle representing a running timer.
     ///
     /// # Safety
@@ -236,7 +229,7 @@ pub unsafe trait UnsafeHrTimerPointer: Sync + Sized {
     ///
     /// Caller promises keep the timer structure alive until the timer is dead.
     /// Caller can ensure this by not leaking the returned [`Self::TimerHandle`].
-    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle;
+    unsafe fn start(self, expires: <Self::TimerMode as HrTimerMode>::Expires) -> Self::TimerHandle;
 }
 
 /// A trait for stack allocated timers.
@@ -246,9 +239,14 @@ pub unsafe trait UnsafeHrTimerPointer: Sync + Sized {
 /// Implementers must ensure that `start_scoped` does not return until the
 /// timer is dead and the timer handler is not running.
 pub unsafe trait ScopedHrTimerPointer {
+    /// The operational mode associated with this timer.
+    ///
+    /// This defines how the expiration value is interpreted.
+    type TimerMode: HrTimerMode;
+
     /// Start the timer to run after `expires` time units and immediately
     /// after call `f`. When `f` returns, the timer is cancelled.
-    fn start_scoped<T, F>(self, expires: Ktime, f: F) -> T
+    fn start_scoped<T, F>(self, expires: <Self::TimerMode as HrTimerMode>::Expires, f: F) -> T
     where
         F: FnOnce() -> T;
 }
@@ -260,7 +258,13 @@ unsafe impl<T> ScopedHrTimerPointer for T
 where
     T: UnsafeHrTimerPointer,
 {
-    fn start_scoped<U, F>(self, expires: Ktime, f: F) -> U
+    type TimerMode = T::TimerMode;
+
+    fn start_scoped<U, F>(
+        self,
+        expires: <<T as UnsafeHrTimerPointer>::TimerMode as HrTimerMode>::Expires,
+        f: F,
+    ) -> U
     where
         F: FnOnce() -> U,
     {
@@ -335,6 +339,11 @@ pub unsafe trait HrTimerHandle {
 /// their documentation. All the methods of this trait must operate on the same
 /// field.
 pub unsafe trait HasHrTimer<T> {
+    /// The operational mode associated with this timer.
+    ///
+    /// This defines how the expiration value is interpreted.
+    type TimerMode: HrTimerMode;
+
     /// Return a pointer to the [`HrTimer`] within `Self`.
     ///
     /// This function is useful to get access to the value without creating
@@ -382,14 +391,14 @@ pub unsafe trait HasHrTimer<T> {
     /// - `this` must point to a valid `Self`.
     /// - Caller must ensure that the pointee of `this` lives until the timer
     ///   fires or is canceled.
-    unsafe fn start(this: *const Self, expires: Ktime) {
+    unsafe fn start(this: *const Self, expires: <Self::TimerMode as HrTimerMode>::Expires) {
         // SAFETY: By function safety requirement, `this` is a valid `Self`.
         unsafe {
             bindings::hrtimer_start_range_ns(
                 Self::c_timer_ptr(this).cast_mut(),
-                expires.to_ns(),
+                expires.as_nanos(),
                 0,
-                (*Self::raw_get_timer(this)).mode.into_c(),
+                <Self::TimerMode as HrTimerMode>::Clock::ID as u32,
             );
         }
     }
@@ -411,80 +420,171 @@ impl HrTimerRestart {
     }
 }
 
-/// Operational mode of [`HrTimer`].
-// NOTE: Some of these have the same encoding on the C side, so we keep
-// `repr(Rust)` and convert elsewhere.
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
-pub enum HrTimerMode {
-    /// Timer expires at the given expiration time.
-    Absolute,
-    /// Timer expires after the given expiration time interpreted as a duration from now.
-    Relative,
-    /// Timer does not move between CPU cores.
-    Pinned,
-    /// Timer handler is executed in soft irq context.
-    Soft,
-    /// Timer handler is executed in hard irq context.
-    Hard,
-    /// Timer expires at the given expiration time.
-    /// Timer does not move between CPU cores.
-    AbsolutePinned,
-    /// Timer expires after the given expiration time interpreted as a duration from now.
-    /// Timer does not move between CPU cores.
-    RelativePinned,
-    /// Timer expires at the given expiration time.
-    /// Timer handler is executed in soft irq context.
-    AbsoluteSoft,
-    /// Timer expires after the given expiration time interpreted as a duration from now.
-    /// Timer handler is executed in soft irq context.
-    RelativeSoft,
-    /// Timer expires at the given expiration time.
-    /// Timer does not move between CPU cores.
-    /// Timer handler is executed in soft irq context.
-    AbsolutePinnedSoft,
-    /// Timer expires after the given expiration time interpreted as a duration from now.
-    /// Timer does not move between CPU cores.
-    /// Timer handler is executed in soft irq context.
-    RelativePinnedSoft,
-    /// Timer expires at the given expiration time.
-    /// Timer handler is executed in hard irq context.
-    AbsoluteHard,
-    /// Timer expires after the given expiration time interpreted as a duration from now.
-    /// Timer handler is executed in hard irq context.
-    RelativeHard,
-    /// Timer expires at the given expiration time.
-    /// Timer does not move between CPU cores.
-    /// Timer handler is executed in hard irq context.
-    AbsolutePinnedHard,
-    /// Timer expires after the given expiration time interpreted as a duration from now.
-    /// Timer does not move between CPU cores.
-    /// Timer handler is executed in hard irq context.
-    RelativePinnedHard,
+/// Time representations that can be used as expiration values in [`HrTimer`].
+pub trait HrTimerExpires {
+    /// Converts the expiration time into a nanosecond representation.
+    ///
+    /// This value corresponds to a raw ktime_t value, suitable for passing to kernel
+    /// timer functions. The interpretation (absolute vs relative) depends on the
+    /// associated [HrTimerMode] in use.
+    fn as_nanos(&self) -> i64;
 }
 
-impl HrTimerMode {
-    fn into_c(self) -> bindings::hrtimer_mode {
-        use bindings::*;
-        match self {
-            HrTimerMode::Absolute => hrtimer_mode_HRTIMER_MODE_ABS,
-            HrTimerMode::Relative => hrtimer_mode_HRTIMER_MODE_REL,
-            HrTimerMode::Pinned => hrtimer_mode_HRTIMER_MODE_PINNED,
-            HrTimerMode::Soft => hrtimer_mode_HRTIMER_MODE_SOFT,
-            HrTimerMode::Hard => hrtimer_mode_HRTIMER_MODE_HARD,
-            HrTimerMode::AbsolutePinned => hrtimer_mode_HRTIMER_MODE_ABS_PINNED,
-            HrTimerMode::RelativePinned => hrtimer_mode_HRTIMER_MODE_REL_PINNED,
-            HrTimerMode::AbsoluteSoft => hrtimer_mode_HRTIMER_MODE_ABS_SOFT,
-            HrTimerMode::RelativeSoft => hrtimer_mode_HRTIMER_MODE_REL_SOFT,
-            HrTimerMode::AbsolutePinnedSoft => hrtimer_mode_HRTIMER_MODE_ABS_PINNED_SOFT,
-            HrTimerMode::RelativePinnedSoft => hrtimer_mode_HRTIMER_MODE_REL_PINNED_SOFT,
-            HrTimerMode::AbsoluteHard => hrtimer_mode_HRTIMER_MODE_ABS_HARD,
-            HrTimerMode::RelativeHard => hrtimer_mode_HRTIMER_MODE_REL_HARD,
-            HrTimerMode::AbsolutePinnedHard => hrtimer_mode_HRTIMER_MODE_ABS_PINNED_HARD,
-            HrTimerMode::RelativePinnedHard => hrtimer_mode_HRTIMER_MODE_REL_PINNED_HARD,
-        }
+impl<C: ClockSource> HrTimerExpires for Instant<C> {
+    #[inline]
+    fn as_nanos(&self) -> i64 {
+        Instant::<C>::as_nanos(self)
+    }
+}
+
+impl HrTimerExpires for Delta {
+    #[inline]
+    fn as_nanos(&self) -> i64 {
+        Delta::as_nanos(*self)
     }
 }
 
+mod private {
+    use crate::time::ClockSource;
+
+    pub trait Sealed {}
+
+    impl<C: ClockSource> Sealed for super::AbsoluteMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativeMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsolutePinnedMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativePinnedMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsoluteSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativeSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsolutePinnedSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativePinnedSoftMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsoluteHardMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativeHardMode<C> {}
+    impl<C: ClockSource> Sealed for super::AbsolutePinnedHardMode<C> {}
+    impl<C: ClockSource> Sealed for super::RelativePinnedHardMode<C> {}
+}
+
+/// Operational mode of [`HrTimer`].
+pub trait HrTimerMode: private::Sealed {
+    /// The C representation of hrtimer mode.
+    const C_MODE: bindings::hrtimer_mode;
+
+    /// Type representing the clock source.
+    type Clock: ClockSource;
+
+    /// Type representing the expiration specification (absolute or relative time).
+    type Expires: HrTimerExpires;
+}
+
+/// Timer that expires at a fixed point in time.
+pub struct AbsoluteMode<C: ClockSource>(PhantomData<C>);
+
+impl<C: ClockSource> HrTimerMode for AbsoluteMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_ABS;
+
+    type Clock = C;
+    type Expires = Instant<C>;
+}
+
+/// Timer that expires after a delay from now.
+pub struct RelativeMode<C: ClockSource>(PhantomData<C>);
+
+impl<C: ClockSource> HrTimerMode for RelativeMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_REL;
+
+    type Clock = C;
+    type Expires = Delta;
+}
+
+/// Timer with absolute expiration time, pinned to its current CPU.
+pub struct AbsolutePinnedMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for AbsolutePinnedMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_ABS_PINNED;
+
+    type Clock = C;
+    type Expires = Instant<C>;
+}
+
+/// Timer with relative expiration time, pinned to its current CPU.
+pub struct RelativePinnedMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for RelativePinnedMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_REL_PINNED;
+
+    type Clock = C;
+    type Expires = Delta;
+}
+
+/// Timer with absolute expiration, handled in soft irq context.
+pub struct AbsoluteSoftMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for AbsoluteSoftMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_ABS_SOFT;
+
+    type Clock = C;
+    type Expires = Instant<C>;
+}
+
+/// Timer with relative expiration, handled in soft irq context.
+pub struct RelativeSoftMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for RelativeSoftMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_REL_SOFT;
+
+    type Clock = C;
+    type Expires = Delta;
+}
+
+/// Timer with absolute expiration, pinned to CPU and handled in soft irq context.
+pub struct AbsolutePinnedSoftMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for AbsolutePinnedSoftMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_ABS_PINNED_SOFT;
+
+    type Clock = C;
+    type Expires = Instant<C>;
+}
+
+/// Timer with absolute expiration, pinned to CPU and handled in soft irq context.
+pub struct RelativePinnedSoftMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for RelativePinnedSoftMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_REL_PINNED_SOFT;
+
+    type Clock = C;
+    type Expires = Delta;
+}
+
+/// Timer with absolute expiration, handled in hard irq context.
+pub struct AbsoluteHardMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for AbsoluteHardMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_ABS_HARD;
+
+    type Clock = C;
+    type Expires = Instant<C>;
+}
+
+/// Timer with relative expiration, handled in hard irq context.
+pub struct RelativeHardMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for RelativeHardMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_REL_HARD;
+
+    type Clock = C;
+    type Expires = Delta;
+}
+
+/// Timer with absolute expiration, pinned to CPU and handled in hard irq context.
+pub struct AbsolutePinnedHardMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for AbsolutePinnedHardMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_ABS_PINNED_HARD;
+
+    type Clock = C;
+    type Expires = Instant<C>;
+}
+
+/// Timer with relative expiration, pinned to CPU and handled in hard irq context.
+pub struct RelativePinnedHardMode<C: ClockSource>(PhantomData<C>);
+impl<C: ClockSource> HrTimerMode for RelativePinnedHardMode<C> {
+    const C_MODE: bindings::hrtimer_mode = bindings::hrtimer_mode_HRTIMER_MODE_REL_PINNED_HARD;
+
+    type Clock = C;
+    type Expires = Delta;
+}
+
 /// Use to implement the [`HasHrTimer<T>`] trait.
 ///
 /// See [`module`] documentation for an example.
@@ -496,12 +596,16 @@ macro_rules! impl_has_hr_timer {
         impl$({$($generics:tt)*})?
             HasHrTimer<$timer_type:ty>
             for $self:ty
-        { self.$field:ident }
+        {
+            mode : $mode:ty,
+            field : self.$field:ident $(,)?
+        }
         $($rest:tt)*
     ) => {
         // SAFETY: This implementation of `raw_get_timer` only compiles if the
         // field has the right type.
         unsafe impl$(<$($generics)*>)? $crate::time::hrtimer::HasHrTimer<$timer_type> for $self {
+            type TimerMode = $mode;
 
             #[inline]
             unsafe fn raw_get_timer(
diff --git a/rust/kernel/time/hrtimer/arc.rs b/rust/kernel/time/hrtimer/arc.rs
index ccf1e66e5b2d..ed490a7a8950 100644
--- a/rust/kernel/time/hrtimer/arc.rs
+++ b/rust/kernel/time/hrtimer/arc.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::sync::Arc;
 use crate::sync::ArcBorrow;
@@ -54,9 +54,13 @@ where
     T: HasHrTimer<T>,
     T: for<'a> HrTimerCallback<Pointer<'a> = Self>,
 {
+    type TimerMode = <T as HasHrTimer<T>>::TimerMode;
     type TimerHandle = ArcHrTimerHandle<T>;
 
-    fn start(self, expires: Ktime) -> ArcHrTimerHandle<T> {
+    fn start(
+        self,
+        expires: <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Expires,
+    ) -> ArcHrTimerHandle<T> {
         // SAFETY:
         //  - We keep `self` alive by wrapping it in a handle below.
         //  - Since we generate the pointer passed to `start` from a valid
diff --git a/rust/kernel/time/hrtimer/pin.rs b/rust/kernel/time/hrtimer/pin.rs
index 2f29fd75d63a..aef16d9ee2f0 100644
--- a/rust/kernel/time/hrtimer/pin.rs
+++ b/rust/kernel/time/hrtimer/pin.rs
@@ -4,7 +4,7 @@ use super::HasHrTimer;
 use super::HrTimer;
 use super::HrTimerCallback;
 use super::HrTimerHandle;
-use super::Ktime;
+use super::HrTimerMode;
 use super::RawHrTimerCallback;
 use super::UnsafeHrTimerPointer;
 use core::pin::Pin;
@@ -54,9 +54,13 @@ where
     T: HasHrTimer<T>,
     T: HrTimerCallback<Pointer<'a> = Self>,
 {
+    type TimerMode = <T as HasHrTimer<T>>::TimerMode;
     type TimerHandle = PinHrTimerHandle<'a, T>;
 
-    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle {
+    unsafe fn start(
+        self,
+        expires: <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Expires,
+    ) -> Self::TimerHandle {
         // Cast to pointer
         let self_ptr: *const T = self.get_ref();
 
diff --git a/rust/kernel/time/hrtimer/pin_mut.rs b/rust/kernel/time/hrtimer/pin_mut.rs
index d05d68be55e9..767d0a4e8a2c 100644
--- a/rust/kernel/time/hrtimer/pin_mut.rs
+++ b/rust/kernel/time/hrtimer/pin_mut.rs
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 use super::{
-    HasHrTimer, HrTimer, HrTimerCallback, HrTimerHandle, Ktime, RawHrTimerCallback,
+    HasHrTimer, HrTimer, HrTimerCallback, HrTimerHandle, HrTimerMode, RawHrTimerCallback,
     UnsafeHrTimerPointer,
 };
 use core::{marker::PhantomData, pin::Pin, ptr::NonNull};
@@ -52,9 +52,13 @@ where
     T: HasHrTimer<T>,
     T: HrTimerCallback<Pointer<'a> = Self>,
 {
+    type TimerMode = <T as HasHrTimer<T>>::TimerMode;
     type TimerHandle = PinMutHrTimerHandle<'a, T>;
 
-    unsafe fn start(mut self, expires: Ktime) -> Self::TimerHandle {
+    unsafe fn start(
+        mut self,
+        expires: <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Expires,
+    ) -> Self::TimerHandle {
         // SAFETY:
         // - We promise not to move out of `self`. We only pass `self`
         //   back to the caller as a `Pin<&mut self>`.
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).