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

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Message-ID: <aA1PjHrG4yT7XpCI@pollux>
Date: Sat, 26 Apr 2025 23:26:36 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: 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, 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 08:30:39PM +0000, Benno Lossin wrote:
> 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...

I can't think of any other error code that would match better, EINVAL seems to
be the correct thing. Maybe one could argue for ENODEV, but I still think EINVAL
fits better.