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From: Andreas Hindborg <a.hindborg@kernel.org>
To: "FUJITA Tomonori" <fujita.tomonori@gmail.com>
Cc: <alex.gaynor@gmail.com>,  <ojeda@kernel.org>,  <aliceryhl@google.com>,
  <anna-maria@linutronix.de>,  <bjorn3_gh@protonmail.com>,
  <boqun.feng@gmail.com>,  <dakr@kernel.org>,  <frederic@kernel.org>,
  <gary@garyguo.net>,  <jstultz@google.com>,
  <linux-kernel@vger.kernel.org>,  <lossin@kernel.org>,
  <lyude@redhat.com>,  <rust-for-linux@vger.kernel.org>,
  <sboyd@kernel.org>,  <tglx@linutronix.de>,  <tmgross@umich.edu>
Subject: Re: [PATCH v3 4/5] rust: time: Make HasHrTimer generic over
 HrTimerMode
In-Reply-To: <20250610132823.3457263-5-fujita.tomonori@gmail.com> (FUJITA
	Tomonori's message of "Tue, 10 Jun 2025 22:28:22 +0900")
References: <20250610132823.3457263-1-fujita.tomonori@gmail.com>
	<aLAKkgBtJFi7eoQFKUAK328qMA9leoq0zggUJFvmVLvPKMS2zd93GP46_ctT_OyR_KidYBqkaweZYPt1sQ4VEQ==@protonmail.internalid>
	<20250610132823.3457263-5-fujita.tomonori@gmail.com>
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Date: Thu, 12 Jun 2025 15:45:43 +0200
Message-ID: <87cyb9xed4.fsf@kernel.org>
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"FUJITA Tomonori" <fujita.tomonori@gmail.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@gmail.com>

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


Best regards,
Andreas Hindborg