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Message-ID: <20251104181924.5a6c3fe7.zhiw@nvidia.com>
Date: Tue, 4 Nov 2025 18:19:24 +0200
From: Zhi Wang <zhiw@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>
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 3/4] rust: pci: add config space read/write
support
On Tue, 04 Nov 2025 16:36:35 +0100
"Danilo Krummrich" <dakr@...nel.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@...nel.org>
> > Signed-off-by: Zhi Wang <zhiw@...dia.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
>
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