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

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Message-ID: <aPtEtbNUdZxhkz6H@google.com>
Date: Fri, 24 Oct 2025 09:19:49 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Danilo Krummrich <dakr@...nel.org>, 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

On Fri, Oct 24, 2025 at 10:25:05AM +0200, Andreas Hindborg wrote:
> "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?

I think it's simpler.

Alice