Re: [PATCH RESEND v4 3/4] rust: pci: add config space read/write support

["Danilo Krummrich" <dakr@kernel.org>]

On Tue Nov 4, 2025 at 3:27 PM CET, Zhi Wang wrote:
> Drivers might need to access PCI config space for querying capability
> structures and access the registers inside the structures.
>
> For Rust drivers need to access PCI config space, the Rust PCI abstraction
> needs to support it in a way that upholds Rust's safety principles.
>
> Introduce a `ConfigSpace` wrapper in Rust PCI abstraction to provide safe
> accessors for PCI config space. The new type implements the `Io` trait to
> share offset validation and bound-checking logic with others.
>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> ---
>  rust/kernel/pci.rs | 148 +++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 142 insertions(+), 6 deletions(-)
>
> diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
> index 77a8eb39ad32..630660a7f05d 100644
> --- a/rust/kernel/pci.rs
> +++ b/rust/kernel/pci.rs
> @@ -5,13 +5,31 @@
>  //! C header: [`include/linux/pci.h`](srctree/include/linux/pci.h)
>  
>  use crate::{
> -    bindings, container_of, device,
> -    device_id::{RawDeviceId, RawDeviceIdIndex},
> +    bindings,
> +    container_of,
> +    device,
> +    device_id::{
> +        RawDeviceId,
> +        RawDeviceIdIndex
> +    },
>      devres::Devres,
>      driver,
> -    error::{from_result, to_result, Result},
> -    io::{Mmio, MmioRaw},
> -    irq::{self, IrqRequest},
> +    error::{
> +        from_result,
> +        to_result,
> +        Result
> +    },
> +    io::{
> +        define_read,
> +        define_write,
> +        Io,
> +        Mmio,
> +        MmioRaw
> +    },
> +    irq::{
> +        self,
> +        IrqRequest
> +    },
>      str::CStr,
>      sync::aref::ARef,
>      types::Opaque,
> @@ -20,7 +38,10 @@
>  use core::{
>      marker::PhantomData,
>      ops::Deref,
> -    ptr::{addr_of_mut, NonNull},
> +    ptr::{
> +        addr_of_mut,
> +        NonNull
> +    },
>  };

Please add a comma and use `//` at the end of the last element of a block as
described in [1]. Otherwise rustfmt will change it up again.

I think most of the diff is not related to this patch. I think it would be good
to convert the whole module and then add further changes.

I just did such a cleanup for the I/O module [1], I can send another patch for
all the PCI stuff.

[1] https://docs.kernel.org/rust/coding-guidelines.html#imports
[2] https://lore.kernel.org/lkml/20251104133301.59402-1-dakr@kernel.org/

>  use kernel::prelude::*;
>  
> @@ -305,6 +326,83 @@ pub struct Device<Ctx: device::DeviceContext = device::Normal>(
>      PhantomData<Ctx>,
>  );
>  
> +/// Represents 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). The actual size is obtained
> +/// from the underlying `struct pci_dev` via [`Device::cfg_size`].
> +pub struct ConfigSpace<'a, const SIZE: usize = { ConfigSpaceSize::Extended as usize }> {
> +    pdev: &'a Device<device::Core>,
> +}
> +
> +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) };
> +        match ret {
> +            0 => val,
> +            _ => !0,
> +        }

I think the match is not needed, the value should already be set accordingly.

> +    }};
> +/// Represents the size of a PCI configuration space.
> +///
> +/// PCI devices can have either a *normal* (legacy) configuration space of 256 bytes,
> +/// or an *extended* configuration space of 4096 bytes as defined in the PCI Express
> +/// specification.
> +pub enum ConfigSpaceSize {

I think this should be [repr(usize)].

> +    /// 256-byte legacy PCI configuration space.
> +    Normal = 256,
> +
> +    /// 4096-byte PCIe extended configuration space.
> +    Extended = 4096,
> +}
> +
>  impl Device {
>      /// Returns the PCI vendor ID as [`Vendor`].
>      ///
> @@ -514,6 +625,17 @@ pub fn pci_class(&self) -> Class {
>          // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`.
>          Class::from_raw(unsafe { (*self.as_raw()).class })
>      }
> +
> +    /// Returns the size of configuration space.
> +    fn cfg_size(&self) -> Result<ConfigSpaceSize> {
> +        // SAFETY: `self.as_raw` is a valid pointer to a `struct pci_dev`.
> +        let size = unsafe { (*self.as_raw()).cfg_size };
> +        match size {
> +            256 => Ok(ConfigSpaceSize::Normal),
> +            4096 => Ok(ConfigSpaceSize::Extended),
> +            _ => Err(EINVAL),

I'd add a debug_assert!() in this case.

> +        }
> +    }
>  }
>  
>  impl Device<device::Bound> {
> @@ -591,6 +713,20 @@ pub fn set_master(&self) {
>          // SAFETY: `self.as_raw` is guaranteed to be a pointer to a valid `struct pci_dev`.
>          unsafe { bindings::pci_set_master(self.as_raw()) };
>      }
> +
> +    /// Return an initialized config space object.
> +    pub fn config_space<'a>(
> +        &'a self,
> +    ) -> Result<ConfigSpace<'a, { ConfigSpaceSize::Normal as usize }>> {

Let's add as_raw() to ConfigSpaceSize and use that instead.

> +        Ok(ConfigSpace { pdev: self })
> +    }
> +
> +    /// Return an initialized config space object.
> +    pub fn config_space_exteneded<'a>(
> +        &'a self,
> +    ) -> Result<ConfigSpace<'a, { ConfigSpaceSize::Extended as usize }>> {
> +        Ok(ConfigSpace { pdev: self })
> +    }
>  }
>  
>  // SAFETY: `Device` is a transparent wrapper of a type that doesn't depend on `Device`'s generic
> -- 
> 2.51.0