linux-kernel - Re: [PATCH v6 05/14] rust: hrtimer: allow timer restart from timer handler

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Message-ID: <87y0zccog2.fsf@kernel.org>
Date: Wed, 15 Jan 2025 12:21:33 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Tamir Duberstein" <tamird@...il.com>
Cc: "Miguel Ojeda" <ojeda@...nel.org>,  "Anna-Maria Behnsen"
 <anna-maria@...utronix.de>,  "Frederic Weisbecker" <frederic@...nel.org>,
  "Thomas Gleixner" <tglx@...utronix.de>,  "Danilo Krummrich"
 <dakr@...nel.org>,  "Alex Gaynor" <alex.gaynor@...il.com>,  "Boqun Feng"
 <boqun.feng@...il.com>,  "Gary Guo" <gary@...yguo.net>,  Björn Roy Baron
 <bjorn3_gh@...tonmail.com>,  "Benno Lossin" <benno.lossin@...ton.me>,
  "Alice Ryhl" <aliceryhl@...gle.com>,  "Trevor Gross" <tmgross@...ch.edu>,
  "Lyude Paul" <lyude@...hat.com>,  "Guangbo Cui" <2407018371@...com>,
  "Dirk Behme" <dirk.behme@...il.com>,  "Daniel Almeida"
 <daniel.almeida@...labora.com>,  <rust-for-linux@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 05/14] rust: hrtimer: allow timer restart from timer
 handler

"Tamir Duberstein" <tamird@...il.com> writes:

> On Fri, Jan 10, 2025 at 3:17 PM Andreas Hindborg <a.hindborg@...nel.org> wrote:
>>
>> 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@...nel.org>
>> ---
>>  rust/kernel/time/hrtimer.rs     | 37 ++++++++++++++++++++++++++++++++++++-
>>  rust/kernel/time/hrtimer/arc.rs |  4 +---
>>  2 files changed, 37 insertions(+), 4 deletions(-)
>>
>> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
>> index d0842c7c4c6ddffeef9a79cbf9727819060e4333..50e8c23578b5cf7196893ac88d9547fc027f1f04 100644
>> --- a/rust/kernel/time/hrtimer.rs
>> +++ b/rust/kernel/time/hrtimer.rs
>> @@ -167,7 +167,7 @@ pub trait HrTimerCallback {
>>      type CallbackTargetParameter<'a>;
>>
>>      /// Called by the timer logic when the timer fires.
>> -    fn run(this: Self::CallbackTargetParameter<'_>)
>> +    fn run(this: Self::CallbackTargetParameter<'_>) -> HrTimerRestart
>>      where
>>          Self: Sized;
>>  }
>> @@ -262,6 +262,41 @@ unsafe fn start(self_ptr: *const Self, expires: Ktime) {
>>      }
>>  }
>>
>> +/// Restart policy for timers.
>> +pub enum HrTimerRestart {
>> +    /// Timer should not be restarted.
>> +    NoRestart,
>> +    /// Timer should be restarted.
>> +    Restart,
>> +}
>> +
>> +impl From<u32> for HrTimerRestart {
>> +    fn from(value: u32) -> Self {
>> +        match value {
>> +            0 => Self::NoRestart,
>> +            _ => Self::Restart,
>> +        }
>> +    }
>> +}
>> +
>> +impl From<i32> for HrTimerRestart {
>> +    fn from(value: i32) -> Self {
>> +        match value {
>> +            0 => Self::NoRestart,
>> +            _ => Self::Restart,
>> +        }
>> +    }
>> +}
>
> These are for converting from bindings to our enum, right? Why do we
> need both signed and unsigned,

Depending on kernel (target arch) configuration, the enum type will be
either signed or unsigned on C side.

I guess I could try to figure out what kernel configs effect the change
and then do conditional compilation on Rust side, but it seems overkill.

> and why do we hardcode 0 rather than
> using the generated constants?

We should use the constants - thanks.


Best regards,
Andreas Hindborg