linux-kernel - Re: [PATCH 3/3] samples: rust: pci: take advantage of Devres::access

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Message-ID: <D9GUSVZY3ZT7.O3RTG4N0ZIK0@proton.me>
Date: Sat, 26 Apr 2025 20:30:39 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Danilo Krummrich <dakr@...nel.org>, gregkh@...uxfoundation.org, rafael@...nel.org, bhelgaas@...gle.com, kwilczynski@...nel.org, zhiw@...dia.com, cjia@...dia.com, jhubbard@...dia.com, bskeggs@...dia.com, acurrid@...dia.com, joelagnelf@...dia.com, ttabi@...dia.com, acourbot@...dia.com, ojeda@...nel.org, alex.gaynor@...il.com, boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...nel.org, aliceryhl@...gle.com, tmgross@...ch.edu
Cc: linux-pci@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] samples: rust: pci: take advantage of Devres::access_with()

On Sat Apr 26, 2025 at 3:30 PM CEST, Danilo Krummrich wrote:
> For the I/O operations executed from the probe() method, take advantage
> of Devres::access_with(), avoiding the atomic check and RCU read lock
> required otherwise entirely.
>
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
> ---
>  samples/rust/rust_driver_pci.rs | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
> index 9ce3a7323a16..3e1569e5096e 100644
> --- a/samples/rust/rust_driver_pci.rs
> +++ b/samples/rust/rust_driver_pci.rs
> @@ -83,12 +83,12 @@ fn probe(pdev: &pci::Device<Core>, info: &Self::IdInfo) -> Result<Pin<KBox<Self>
>              GFP_KERNEL,
>          )?;
>  
> -        let res = drvdata
> -            .bar
> -            .try_access_with(|b| Self::testdev(info, b))
> -            .ok_or(ENXIO)??;
> -
> -        dev_info!(pdev.as_ref(), "pci-testdev data-match count: {}\n", res);
> +        let bar = drvdata.bar.access_with(pdev.as_ref())?;

Since this code might inspire other code, I don't think that we should
return `EINVAL` here (bubbled up from `access_with`). Not sure what the
correct thing here would be though...

---
Cheers,
Benno

> +        dev_info!(
> +            pdev.as_ref(),
> +            "pci-testdev data-match count: {}\n",
> +            Self::testdev(info, bar)?
> +        );
>  
>          Ok(drvdata.into())
>      }