linux-kernel - Re: [PATCH v1 2/2] rust: Add read_poll

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Message-Id: <DC0YN6WQFUQY.3PKYK23ESRJQL@nvidia.com>
Date: Wed, 13 Aug 2025 11:56:26 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "FUJITA Tomonori" <fujita.tomonori@...il.com>, <a.hindborg@...nel.org>,
 <alex.gaynor@...il.com>, <ojeda@...nel.org>
Cc: <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>, <daniel.almeida@...labora.com>, "Fiona Behrens"
 <me@...enk.dev>
Subject: Re: [PATCH v1 2/2] rust: Add read_poll_timeout functions

On Mon Aug 11, 2025 at 1:10 PM JST, FUJITA Tomonori wrote:
> Add read_poll_timeout functions which poll periodically until a

"functions" should be the singular "function" as this patch only adds
one function.

<snip>
> +/// # Examples
> +///
> +/// ```no_run
> +/// use kernel::io::Io;
> +/// use kernel::time::{poll::read_poll_timeout, Delta};
> +///
> +/// const HW_READY: u16 = 0x01;
> +///
> +/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result<()> {
> +///     // The `op` closure reads the value of a specific status register.
> +///     let op = || -> Result<u16> { io.try_read16(0x1000) };
> +///
> +///     // The `cond` closure takes a reference to the value returned by `op`
> +///     // and checks whether the hardware is ready.
> +///     let cond = |val: &u16| *val == HW_READY;
> +///
> +///     match read_poll_timeout(op, cond, Delta::from_millis(50), Some(Delta::from_secs(3))) {

Is there a reason for not writing the closures directly inline? I.e.

  match read_poll_timeout(
      // 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| *val == HW_READY,
      Delta::from_millis(50),
      Some(Delta::from_secs(3))
  )

I think it is closer to how people will actually use this function, and
the expected types for the closures are available right in the function
definition if they need more details.