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

[Zhi Wang <zhiw@nvidia.com>]

On Tue, 04 Nov 2025 16:36:35 +0100
"Danilo Krummrich" <dakr@kernel.org> wrote:

> 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 see.

> 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.
> 

I can rebase this series on top of yours once your sent them out. 

> [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
>