linux-kernel - Re: [PATCH v2 2/2] rust: Add read_poll_count

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Message-ID: <871pmshfku.fsf@t14s.mail-host-address-is-not-set>
Date: Fri, 24 Oct 2025 10:25:05 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>, Danilo Krummrich <dakr@...nel.org>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>,
 daniel.almeida@...labora.com, alex.gaynor@...il.com, ojeda@...nel.org,
 anna-maria@...utronix.de, bjorn3_gh@...tonmail.com, boqun.feng@...il.com,
 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 v2 2/2] rust: Add read_poll_count_atomic function

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> On Tue, Oct 21, 2025 at 02:35:34PM +0200, Danilo Krummrich wrote:
>> On Tue Oct 21, 2025 at 9:11 AM CEST, FUJITA Tomonori wrote:
>> > +/// Polls periodically until a condition is met, an error occurs,
>> > +/// or the attempt limit is reached.
>> > +///
>> > +/// The function repeatedly executes the given operation `op` closure and
>> > +/// checks its result using the condition closure `cond`.
>> > +///
>> > +/// If `cond` returns `true`, the function returns successfully with the result of `op`.
>> > +/// Otherwise, it performs a busy wait for a duration specified by `delay_delta`
>> > +/// before executing `op` again.
>> > +///
>> > +/// This process continues until either `op` returns an error, `cond`
>> > +/// returns `true`, or the attempt limit specified by `count` is reached.
>> > +///
>> > +/// # Errors
>> > +///
>> > +/// If `op` returns an error, then that error is returned directly.
>> > +///
>> > +/// If the attempt limit specified by `count` is reached, then
>> > +/// `Err(ETIMEDOUT)` is returned.
>> > +///
>> > +/// # Examples
>> > +///
>> > +/// ```no_run
>> > +/// use kernel::io::{Io, poll::read_poll_count_atomic};
>> > +/// use kernel::time::Delta;
>> > +///
>> > +/// const HW_READY: u16 = 0x01;
>> > +///
>> > +/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
>> > +///     match read_poll_count_atomic(
>> > +///         // The `op` closure reads the value of a specific status register.
>> > +///         || io.try_read16(0x1000),
>> > +///         // The `cond` closure takes a reference to the value returned by `op`
>> > +///         // and checks whether the hardware is ready.
>> > +///         |val: &u16| *val == HW_READY,
>> > +///         Delta::from_micros(50),
>> > +///         1000,
>> > +///     ) {
>> > +///         Ok(_) => {
>> > +///             // The hardware is ready. The returned value of the `op` closure
>> > +///             // isn't used.
>> > +///             Ok(())
>> > +///         }
>> > +///         Err(e) => Err(e),
>> > +///     }
>>
>> Please replace the match statement with map().
>>
>> 	read_poll_count_atomic(
>> 	    ...
>> 	)
>> 	.map(|_| ())
>>
>
> IMO, this should instead be:
>
> 	read_poll_count_atomic(
> 	    ...
> 	)?
> 	Ok(())

It does not really matter to me. Why do you prefer one to the other?


Best regards,
Andreas Hindborg