linux-kernel - Re: [PATCH v3 4/5] rust: time: Make HasHrTimer generic over HrTimerMode

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Message-ID: <87cyb9xed4.fsf@kernel.org>
Date: Thu, 12 Jun 2025 15:45:43 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "FUJITA Tomonori" <fujita.tomonori@...il.com>
Cc: <alex.gaynor@...il.com>,  <ojeda@...nel.org>,  <aliceryhl@...gle.com>,
  <anna-maria@...utronix.de>,  <bjorn3_gh@...tonmail.com>,
  <boqun.feng@...il.com>,  <dakr@...nel.org>,  <frederic@...nel.org>,
  <gary@...yguo.net>,  <jstultz@...gle.com>,
  <linux-kernel@...r.kernel.org>,  <lossin@...nel.org>,
  <lyude@...hat.com>,  <rust-for-linux@...r.kernel.org>,
  <sboyd@...nel.org>,  <tglx@...utronix.de>,  <tmgross@...ch.edu>
Subject: Re: [PATCH v3 4/5] rust: time: Make HasHrTimer generic over
 HrTimerMode

"FUJITA Tomonori" <fujita.tomonori@...il.com> writes:

> 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@...il.com>

Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>


Best regards,
Andreas Hindborg