linux-kernel - Re: [PATCH v6 RESEND 6/7] rust: pci: add config space read/write support

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Message-ID: <20251114002005.GA2384907@joelbox2>
Date: Thu, 13 Nov 2025 19:20:05 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: Zhi Wang <zhiw@...dia.com>
Cc: rust-for-linux@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, dakr@...nel.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, jhubbard@...dia.com, zhiwang@...nel.org
Subject: Re: [PATCH v6 RESEND 6/7] rust: pci: add config space read/write
 support

Hi Zhi,

On Mon, Nov 10, 2025 at 10:41:18PM +0200, Zhi Wang wrote:
[..]  
>  impl Device<device::Core> {
> diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
> index 2bbb3261198d..bb78a83fe92c 100644
> --- a/rust/kernel/pci/io.rs
> +++ b/rust/kernel/pci/io.rs
> @@ -2,12 +2,19 @@
>  
>  //! PCI memory-mapped I/O infrastructure.
>  
> -use super::Device;
> +use super::{
> +    ConfigSpaceSize,
> +    Device, //
> +};
>  use crate::{
>      bindings,
>      device,
>      devres::Devres,
>      io::{
> +        define_read,
> +        define_write,
> +        Io,
> +        IoInfallible,
>          Mmio,
>          MmioRaw, //
>      },
> @@ -16,6 +23,58 @@
>  };
>  use core::ops::Deref;
>  
> +/// The PCI configuration space of a device.
> +///
> +/// Provides typed read and write accessors for configuration registers
> +/// using the standard `pci_read_config_*` and `pci_write_config_*` helpers.
> +///
> +/// The generic const parameter `SIZE` can be used to indicate the
> +/// maximum size of the configuration space (e.g. 256 bytes for legacy,
> +/// 4096 bytes for extended config space).
> +pub struct ConfigSpace<'a, const SIZE: usize = { ConfigSpaceSize::Extended as usize }> {
> +    pub(crate) pdev: &'a Device<device::Bound>,
> +}
> +
> +macro_rules! call_config_read {
> +    (infallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr) => {{
> +        let mut val: $ty = 0;
> +        let _ret = unsafe { bindings::$c_fn($self.pdev.as_raw(), $addr as i32, &mut val) };
> +        val
> +    }};
> +}
> +
> +macro_rules! call_config_write {
> +    (infallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr, $value:expr) => {
> +        let _ret = unsafe { bindings::$c_fn($self.pdev.as_raw(), $addr as i32, $value) };

unsafe block needs safety comments, also I understand 'as' to convert is
generally forbidden without a CAST: comment or using ::from() for conversion
because it can by a lossy conversion.

Also we should have a comment on why its safe for _ret to be ignored.
Basically what guarantees that the call is really infallible? Anything we can
do to ensure errors are not silently ignored? Let me know if I missed
something.

[..]

> +
> +    /// Return an initialized config space object.
> +    pub fn config_space_exteneded<'a>(

typo in func name.

thanks,

 - Joel

> +        &'a self,
> +    ) -> Result<ConfigSpace<'a, { ConfigSpaceSize::Extended.as_raw() }>> {
> +        Ok(ConfigSpace { pdev: self })
> +    }
>  }
> -- 
> 2.51.0
>