linux-kernel - Re: [PATCH RESEND v4 4/4] sample: rust: pci: add tests for config space routines

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Message-Id: <DE00WIVOSYC2.2CAGWUYWE6FZ@kernel.org>
Date: Tue, 04 Nov 2025 16:41:56 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Zhi Wang" <zhiw@...dia.com>
Cc: <rust-for-linux@...r.kernel.org>, <linux-pci@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <aliceryhl@...gle.com>,
 <bhelgaas@...gle.com>, <kwilczynski@...nel.org>, <ojeda@...nel.org>,
 <alex.gaynor@...il.com>, <boqun.feng@...il.com>, <gary@...yguo.net>,
 <bjorn3_gh@...tonmail.com>, <lossin@...nel.org>, <a.hindborg@...nel.org>,
 <tmgross@...ch.edu>, <markus.probst@...teo.de>, <helgaas@...nel.org>,
 <cjia@...dia.com>, <smitra@...dia.com>, <ankita@...dia.com>,
 <aniketa@...dia.com>, <kwankhede@...dia.com>, <targupta@...dia.com>,
 <acourbot@...dia.com>, <joelagnelf@...dia.com>, <jhubbard@...dia.com>,
 <zhiwang@...nel.org>
Subject: Re: [PATCH RESEND v4 4/4] sample: rust: pci: add tests for config
 space routines

On Tue Nov 4, 2025 at 3:27 PM CET, Zhi Wang wrote:
> +    fn config_space(pdev: &pci::Device<Core>) -> Result {
> +        let config = pdev.config_space()?;
> +
> +        // TODO: use the register!() macro for defining PCI configuration space registers once it
> +        // has been move out of nova-core.
> +        dev_info!(
> +            pdev.as_ref(),
> +            "pci-testdev config space read8 rev ID: {:x}\n",
> +            config.read8(0x8)
> +        );
> +
> +        dev_info!(
> +            pdev.as_ref(),
> +            "pci-testdev config space read16 vendor ID: {:x}\n",
> +            config.read16(0)
> +        );
> +
> +        dev_info!(
> +            pdev.as_ref(),
> +            "pci-testdev config space read32 BAR 0: {:x}\n",
> +            config.read32(0x10)
> +        );
> +
> +        dev_info!(
> +            pdev.as_ref(),
> +            "pci-testdev config space try_read8 rev ID: {:x}\n",
> +            config.try_read8(0x8)?
> +        );
> +
> +        dev_info!(
> +            pdev.as_ref(),
> +            "pci-testdev config space try_read16 vendor ID: {:x}\n",
> +            config.try_read16(0)?
> +        );
> +
> +        dev_info!(
> +            pdev.as_ref(),
> +            "pci-testdev config space try_read32 BAR 0: {:x}\n",
> +            config.try_read32(0x10)?
> +        );

If we want to demonstrate the fallible accessors we should try accesses outside
the bounds of the requested config space size. However, that doesn't really make
sense, because in this case the driver could have been calling
config_space_extended() instead.

So, I think the fallible versions don't really serve a purpose and we should
probably drop them.