[PATCH v11 0/5] rust: pci: add config space read/write support

[PATCH v11 0/5] rust: pci: add config space read/write support

[Zhi Wang]

In the NVIDIA vGPU RFC [1], the PCI configuration space access is
required in nova-core for preparing gspVFInfo when vGPU support is
enabled. This series is the following up of the discussion with Danilo
for how to introduce support of PCI configuration space access in Rust
PCI abstractions. Alice/Alex/I had a discussion of the next steps of
this patch series in LPC 2025. We agreed that first introducing the
functionality before the BoundedInteger work and other refinement is
settled. [2]

The repo with the patches can be found at [3].

v11:

I tried to combine IoCapable and IoTryCapable. I found I have to dump
the original forwarding call scheme.

In this re-spin, I moved the accessors into the Io/IoKnownSize traits
and I have to added the default trait functions required by the
compiler. The IoCapable<T> turns into a pure marker trait. Reaching
the accessors from a driver are restricted by the where statements
marked by IoCapable<T>. A backend marks its capablities via implementing
IoCapable<T>. This is quite close to Gary's orginal suggestions.

I also left a assert in the default trait functions (accessors) to
catch the case that a backend implements IoCapable<T> to claim it
support the accessors but forgets to implement the accessors. This
should be helpful when developing a new backend.

- Combine IoCapable and IoTryCapable. (Danilo/Gary)
- Keep IoKnownSize trait. (Alice/Gary)
- Fix the compiling error in pwm_th1520 driver.

v10:

- Merge IoBase trait into Io trait to simplify trait hierarchy.
- Use IoCapable<T> and IoTryCapable<T> functional traits (not marker
  traits) to separate infallible and fallible I/O operations. (Danilo/Gary)

I tried implementing the marker traits idea, but I found that the
compiler still requires a default implementation for each function in
the main trait to avoid forcing backends to implement unsupported
methods.

However, Gary's core idea of "capabilities" is extremely valuable. So, I
adopted a dispatching pattern:

- All I/O accessors are defined in the Io trait. They use default
  implementations to dispatch calls to the underlying IoCapable and
  IoTryCapable traits.

This addresses Alice's concern about the complicated trait hierarchy.

It preserves strict compile-time static checks. The compiler can catch
the case if a driver calls an accessor not implemented by a backend.

- The actual logic resides in IoCapable<T> and IoTryCapable<T>.

Backends can selectively implement IoCapable<T> or IoTryCapable<T> based
on hardware support.

This addresses Markus's concern regarding backends with limited access
sizes (e.g., I2C).

For example, the Mmio backend implements both IoCapable and IoTryCapable
for all sizes, while the PCI config space backend only implements
IoCapable for u8/u16/u32.

v9:

- Rebase the patches to the latest driver-core-testing.
- Move ConfigSpaceSize to pci/io.rs. (Danilo)
- Refine docs. (Danilo)
- Compiling test on Tyr. (Danilo)

v8:

- Rebase to latest driver-core-testing branch.
- Refinement of traits name and hierarchy: (Alice)
  * Rename IoInfallible trait to IoKnownSize trait.
  * Keep Infallible helpers in Io trait.

v7:

- Rebase to latest driver-core-testing branch.
- Introduce Io64 trait. (Alice)
- Add docs for call_{mmio, config}_{read, write}() macros. (Alex)
- Improve the define_{read, write} macros. (Alex)
- Add SAFETY/CAST in call_config_{read, write}. (Joel)
- Fix typo of method name. (Alex/Joel)

v6:

- Implement config_space() and config_space_extended() in device::Bound
  lifecycle. (Danilo)
- Fix the "use" in the comment for generating proper rust docs, verify
  the output of rustdoc. (Miguel)
- Improve the comments of PCI configuration space when checking the
  output of rustdoc.

v5:

- Remove fallible accessors of PCI configuration space. (Danilo)
- Add #[repr(usize)] for enum ConfigSpace. (Danilo)
- Refine the handling of return value in read accessors. (Danilo)
- Add debug_assert!() in pdev::cfg_size(). (Danilo)
- Add ConfigSpace.as_raw() for extracting the raw value. (Danilo)
- Rebase the patches on top of driver-core-testing branch.
- Convert imports touched by this series to vertical style.

v4:

- Refactor the SIZE constant to be an associated constant. (Alice)
- Remove the default method implementations in the Io trait. (Alice)
- Make cfg_size() private. (Danilo/Bjorn)
- Implement the infallible accessors of ConfigSpace. (Danilo)
- Create a new Io64 trait specifically for 64-bit accessors. (Danilo)
- Provide two separate methods for driver: config_space() and
  config_space_extended(). (Danilo)
- Update the sample driver to test the infallible accessors. (Danilo)

v3:

- Turn offset_valid() into a private function of kernel::io:Io. (Alex)
- Separate try and non-try variants. (Danilo)
- Move all the {try_}{read,write}{8,16,32,64} accessors to the I/O trait.
  (Danilo)
- Replace the hardcoded MMIO type constraint with a generic trait bound
  so that register! macro can be used in other places. (Danilo)
- Fix doctest. (John)
- Add an enum for PCI configuration space size. (Danilo)
- Refine the patch comments. (Bjorn)

v2:

- Factor out common trait as 'Io' and keep the rest routines in original
  'Io' as 'Mmio'. (Danilo)
- Rename 'IoRaw' to 'MmioRaw'. Update the bus MMIO implementation to use
  'MmioRaw'.
- Introduce pci::Device<Bound>::config_space(). (Danilo)
- Implement both infallible and fallible read/write routines, the device
  driver decicdes which version should be used.

This ideas of this series are:

- Factor out common traits for other accessors to share the same
  compiling/runtime check like before.

- Introduce IoCapable<T> and IoTryCapable<T> traits to allow backends
  to selectively implement only the operations they support.

- Factor the MMIO read/write macros from the define_read! and
  define_write! macros. Thus, define_{read, write}! can be used in other
  backends.

  In detail:

  * Introduce `call_mmio_read!` and `call_mmio_write!` helper macros
    to encapsulate the unsafe FFI calls.
  * Update `define_read!` and `define_write!` macros to delegate to
    the call macros.
  * Export `define_read` and `define_write` so they can be reused
    for other I/O backends (e.g. PCI config space).

- Implement the PCI configuration space access backend in PCI
  abstractions.

- Add tests for config space routines in rust PCI sample driver.

[1] https://lore.kernel.org/all/20250903221111.3866249-1-zhiw@nvidia.com/
[2] https://lore.kernel.org/all/DEOMBKIRDXH6.2CF2MR2RB2W2C@nvidia.com/
[3] https://github.com/zhiwang-nvidia/nova-core/tree/rust-for-linux/pci-configuration-space-v11

Zhi Wang (5):
  rust: devres: style for imports
  rust: io: separate generic I/O helpers from MMIO implementation
  rust: io: factor out MMIO read/write macros
  rust: pci: add config space read/write support
  sample: rust: pci: add tests for config space routines

 drivers/gpu/drm/tyr/regs.rs            |   1 +
 drivers/gpu/nova-core/gsp/sequencer.rs |   5 +-
 drivers/gpu/nova-core/regs/macros.rs   |  90 +++--
 drivers/gpu/nova-core/vbios.rs         |   1 +
 drivers/pwm/pwm_th1520.rs              |   5 +-
 rust/kernel/devres.rs                  |  35 +-
 rust/kernel/io.rs                      | 494 +++++++++++++++++++++----
 rust/kernel/io/mem.rs                  |  16 +-
 rust/kernel/io/poll.rs                 |  16 +-
 rust/kernel/pci/io.rs                  | 171 ++++++++-
 samples/rust/rust_driver_pci.rs        |  32 ++
 11 files changed, 722 insertions(+), 144 deletions(-)

-- 
2.51.0

[PATCH v11 1/5] rust: devres: style for imports

[Zhi Wang]

Convert all imports in the devres to use "kernel vertical" style.

Cc: Gary Guo <gary@garyguo.net>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 rust/kernel/devres.rs | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index db02f8b1788d..43089511bf76 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -254,8 +254,12 @@ pub fn device(&self) -> &Device {
     /// # Examples
     ///
     /// ```no_run
-    /// # #![cfg(CONFIG_PCI)]
-    /// # use kernel::{device::Core, devres::Devres, pci};
+    /// #![cfg(CONFIG_PCI)]
+    /// use kernel::{
+    ///     device::Core,
+    ///     devres::Devres,
+    ///     pci, //
+    /// };
     ///
     /// fn from_core(dev: &pci::Device<Core>, devres: Devres<pci::Bar<0x4>>) -> Result {
     ///     let bar = devres.access(dev.as_ref())?;
@@ -358,7 +362,13 @@ fn register_foreign<P>(dev: &Device<Bound>, data: P) -> Result
 /// # Examples
 ///
 /// ```no_run
-/// use kernel::{device::{Bound, Device}, devres};
+/// use kernel::{
+///     device::{
+///         Bound,
+///         Device, //
+///     },
+///     devres, //
+/// };
 ///
 /// /// Registration of e.g. a class device, IRQ, etc.
 /// struct Registration;
-- 
2.51.0

Re: [PATCH v11 1/5] rust: devres: style for imports

[Gary Guo]

On Wed Jan 21, 2026 at 2:23 PM GMT, Zhi Wang wrote:
> Convert all imports in the devres to use "kernel vertical" style.
>
> Cc: Gary Guo <gary@garyguo.net>
> Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
> Signed-off-by: Zhi Wang <zhiw@nvidia.com>

It does not look like this patch has been changed but yet you didn't pick up my
R-b tag.

Also this is still using the wrong email address for Miguel without using
the .mailmap.

Best,
Gary

> ---
>  rust/kernel/devres.rs | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
> index db02f8b1788d..43089511bf76 100644
> --- a/rust/kernel/devres.rs
> +++ b/rust/kernel/devres.rs
> @@ -254,8 +254,12 @@ pub fn device(&self) -> &Device {
>      /// # Examples
>      ///
>      /// ```no_run
> -    /// # #![cfg(CONFIG_PCI)]
> -    /// # use kernel::{device::Core, devres::Devres, pci};
> +    /// #![cfg(CONFIG_PCI)]
> +    /// use kernel::{
> +    ///     device::Core,
> +    ///     devres::Devres,
> +    ///     pci, //
> +    /// };
>      ///
>      /// fn from_core(dev: &pci::Device<Core>, devres: Devres<pci::Bar<0x4>>) -> Result {
>      ///     let bar = devres.access(dev.as_ref())?;
> @@ -358,7 +362,13 @@ fn register_foreign<P>(dev: &Device<Bound>, data: P) -> Result
>  /// # Examples
>  ///
>  /// ```no_run
> -/// use kernel::{device::{Bound, Device}, devres};
> +/// use kernel::{
> +///     device::{
> +///         Bound,
> +///         Device, //
> +///     },
> +///     devres, //
> +/// };
>  ///
>  /// /// Registration of e.g. a class device, IRQ, etc.
>  /// struct Registration;

Re: [PATCH v11 1/5] rust: devres: style for imports

[Zhi Wang]

On Wed, 21 Jan 2026 14:54:16 +0000
"Gary Guo" <gary@garyguo.net> wrote:

> On Wed Jan 21, 2026 at 2:23 PM GMT, Zhi Wang wrote:
> > Convert all imports in the devres to use "kernel vertical" style.
> >
> > Cc: Gary Guo <gary@garyguo.net>
> > Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
> > Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> 
> It does not look like this patch has been changed but yet you didn't
> pick up my R-b tag.
> 
> Also this is still using the wrong email address for Miguel without using
> the .mailmap.
> 

Oh, this piece must be missed during the rebasing. Will fix it in the next
re-spin.

> Best,
> Gary
> 
> > ---
> >  rust/kernel/devres.rs | 16 +++++++++++++---
> >  1 file changed, 13 insertions(+), 3 deletions(-)
> >
> > diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
> > index db02f8b1788d..43089511bf76 100644
> > --- a/rust/kernel/devres.rs
> > +++ b/rust/kernel/devres.rs
> > @@ -254,8 +254,12 @@ pub fn device(&self) -> &Device {
> >      /// # Examples
> >      ///
> >      /// ```no_run
> > -    /// # #![cfg(CONFIG_PCI)]
> > -    /// # use kernel::{device::Core, devres::Devres, pci};
> > +    /// #![cfg(CONFIG_PCI)]
> > +    /// use kernel::{
> > +    ///     device::Core,
> > +    ///     devres::Devres,
> > +    ///     pci, //
> > +    /// };
> >      ///
> >      /// fn from_core(dev: &pci::Device<Core>, devres:
> > Devres<pci::Bar<0x4>>) -> Result { ///     let bar =
> > devres.access(dev.as_ref())?; @@ -358,7 +362,13 @@ fn
> > register_foreign<P>(dev: &Device<Bound>, data: P) -> Result /// #
> > Examples ///
> >  /// ```no_run
> > -/// use kernel::{device::{Bound, Device}, devres};
> > +/// use kernel::{
> > +///     device::{
> > +///         Bound,
> > +///         Device, //
> > +///     },
> > +///     devres, //
> > +/// };
> >  ///
> >  /// /// Registration of e.g. a class device, IRQ, etc.
> >  /// struct Registration;
> 

[PATCH v11 2/5] rust: io: separate generic I/O helpers from MMIO implementation

[Zhi Wang]

The previous Io<SIZE> type combined both the generic I/O access helpers
and MMIO implementation details in a single struct. This coupling prevented
reusing the I/O helpers for other backends, such as PCI configuration
space.

Establish a clean separation between the I/O interface and concrete backends
by separating generic I/O helpers from MMIO implementation.

Introduce a new trait hierarchy to handle different access capabilities:

- IoCapable<T>: A marker trait indicating that a backend supports I/O
  operations of a certain type (u8, u16, u32, or u64).

- Io trait: Defines fallible I/O methods (try_read8, try_write8, etc.) with
  runtime bounds checking.

- IoKnownSize trait: Extends Io to define infallible I/O methods (read8,
  write8, etc.) with compile-time bounds checking for regions where the
  size is known at compile time.

Move the MMIO-specific logic into a dedicated Mmio<SIZE> type that
implements the Io and IoKnownSize traits. Rename IoRaw to MmioRaw and
update consumers to use the new types.

Cc: Alexandre Courbot <acourbot@nvidia.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>
Cc: Gary Guo <gary@garyguo.net>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 drivers/gpu/drm/tyr/regs.rs            |   1 +
 drivers/gpu/nova-core/gsp/sequencer.rs |   5 +-
 drivers/gpu/nova-core/regs/macros.rs   |  90 +++---
 drivers/gpu/nova-core/vbios.rs         |   1 +
 drivers/pwm/pwm_th1520.rs              |   5 +-
 rust/kernel/devres.rs                  |  19 +-
 rust/kernel/io.rs                      | 415 +++++++++++++++++++++----
 rust/kernel/io/mem.rs                  |  16 +-
 rust/kernel/io/poll.rs                 |  16 +-
 rust/kernel/pci/io.rs                  |  12 +-
 samples/rust/rust_driver_pci.rs        |   4 +
 11 files changed, 453 insertions(+), 131 deletions(-)

diff --git a/drivers/gpu/drm/tyr/regs.rs b/drivers/gpu/drm/tyr/regs.rs
index f46933aaa221..9f89bc73a775 100644
--- a/drivers/gpu/drm/tyr/regs.rs
+++ b/drivers/gpu/drm/tyr/regs.rs
@@ -11,6 +11,7 @@
 use kernel::device::Bound;
 use kernel::device::Device;
 use kernel::devres::Devres;
+use kernel::io::IoKnownSize;
 use kernel::prelude::*;
 
 use crate::driver::IoMem;
diff --git a/drivers/gpu/nova-core/gsp/sequencer.rs b/drivers/gpu/nova-core/gsp/sequencer.rs
index 2d0369c49092..862cf7f27143 100644
--- a/drivers/gpu/nova-core/gsp/sequencer.rs
+++ b/drivers/gpu/nova-core/gsp/sequencer.rs
@@ -12,7 +12,10 @@
 
 use kernel::{
     device,
-    io::poll::read_poll_timeout,
+    io::{
+        poll::read_poll_timeout,
+        Io, //
+    },
     prelude::*,
     time::{
         delay::fsleep,
diff --git a/drivers/gpu/nova-core/regs/macros.rs b/drivers/gpu/nova-core/regs/macros.rs
index fd1a815fa57d..ed624be1f39b 100644
--- a/drivers/gpu/nova-core/regs/macros.rs
+++ b/drivers/gpu/nova-core/regs/macros.rs
@@ -369,16 +369,18 @@ impl $name {
 
             /// Read the register from its address in `io`.
             #[inline(always)]
-            pub(crate) fn read<const SIZE: usize, T>(io: &T) -> Self where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+            pub(crate) fn read<T, I>(io: &T) -> Self where
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
             {
                 Self(io.read32($offset))
             }
 
             /// Write the value contained in `self` to the register address in `io`.
             #[inline(always)]
-            pub(crate) fn write<const SIZE: usize, T>(self, io: &T) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+            pub(crate) fn write<T, I>(self, io: &T) where
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
             {
                 io.write32(self.0, $offset)
             }
@@ -386,11 +388,12 @@ pub(crate) fn write<const SIZE: usize, T>(self, io: &T) where
             /// Read the register from its address in `io` and run `f` on its value to obtain a new
             /// value to write back.
             #[inline(always)]
-            pub(crate) fn update<const SIZE: usize, T, F>(
+            pub(crate) fn update<T, I, F>(
                 io: &T,
                 f: F,
             ) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 F: ::core::ops::FnOnce(Self) -> Self,
             {
                 let reg = f(Self::read(io));
@@ -408,12 +411,13 @@ impl $name {
             /// Read the register from `io`, using the base address provided by `base` and adding
             /// the register's offset to it.
             #[inline(always)]
-            pub(crate) fn read<const SIZE: usize, T, B>(
+            pub(crate) fn read<T, I, B>(
                 io: &T,
                 #[allow(unused_variables)]
                 base: &B,
             ) -> Self where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
             {
                 const OFFSET: usize = $name::OFFSET;
@@ -428,13 +432,14 @@ pub(crate) fn read<const SIZE: usize, T, B>(
             /// Write the value contained in `self` to `io`, using the base address provided by
             /// `base` and adding the register's offset to it.
             #[inline(always)]
-            pub(crate) fn write<const SIZE: usize, T, B>(
+            pub(crate) fn write<T, I, B>(
                 self,
                 io: &T,
                 #[allow(unused_variables)]
                 base: &B,
             ) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
             {
                 const OFFSET: usize = $name::OFFSET;
@@ -449,12 +454,13 @@ pub(crate) fn write<const SIZE: usize, T, B>(
             /// the register's offset to it, then run `f` on its value to obtain a new value to
             /// write back.
             #[inline(always)]
-            pub(crate) fn update<const SIZE: usize, T, B, F>(
+            pub(crate) fn update<T, I, B, F>(
                 io: &T,
                 base: &B,
                 f: F,
             ) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
                 F: ::core::ops::FnOnce(Self) -> Self,
             {
@@ -474,11 +480,12 @@ impl $name {
 
             /// Read the array register at index `idx` from its address in `io`.
             #[inline(always)]
-            pub(crate) fn read<const SIZE: usize, T>(
+            pub(crate) fn read<T, I>(
                 io: &T,
                 idx: usize,
             ) -> Self where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
             {
                 build_assert!(idx < Self::SIZE);
 
@@ -490,12 +497,13 @@ pub(crate) fn read<const SIZE: usize, T>(
 
             /// Write the value contained in `self` to the array register with index `idx` in `io`.
             #[inline(always)]
-            pub(crate) fn write<const SIZE: usize, T>(
+            pub(crate) fn write<T, I>(
                 self,
                 io: &T,
                 idx: usize
             ) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
             {
                 build_assert!(idx < Self::SIZE);
 
@@ -507,12 +515,13 @@ pub(crate) fn write<const SIZE: usize, T>(
             /// Read the array register at index `idx` in `io` and run `f` on its value to obtain a
             /// new value to write back.
             #[inline(always)]
-            pub(crate) fn update<const SIZE: usize, T, F>(
+            pub(crate) fn update<T, I, F>(
                 io: &T,
                 idx: usize,
                 f: F,
             ) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 F: ::core::ops::FnOnce(Self) -> Self,
             {
                 let reg = f(Self::read(io, idx));
@@ -524,11 +533,12 @@ pub(crate) fn update<const SIZE: usize, T, F>(
             /// The validity of `idx` is checked at run-time, and `EINVAL` is returned is the
             /// access was out-of-bounds.
             #[inline(always)]
-            pub(crate) fn try_read<const SIZE: usize, T>(
+            pub(crate) fn try_read<T, I>(
                 io: &T,
                 idx: usize,
             ) -> ::kernel::error::Result<Self> where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
             {
                 if idx < Self::SIZE {
                     Ok(Self::read(io, idx))
@@ -542,12 +552,13 @@ pub(crate) fn try_read<const SIZE: usize, T>(
             /// The validity of `idx` is checked at run-time, and `EINVAL` is returned is the
             /// access was out-of-bounds.
             #[inline(always)]
-            pub(crate) fn try_write<const SIZE: usize, T>(
+            pub(crate) fn try_write<T, I>(
                 self,
                 io: &T,
                 idx: usize,
             ) -> ::kernel::error::Result where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
             {
                 if idx < Self::SIZE {
                     Ok(self.write(io, idx))
@@ -562,12 +573,13 @@ pub(crate) fn try_write<const SIZE: usize, T>(
             /// The validity of `idx` is checked at run-time, and `EINVAL` is returned is the
             /// access was out-of-bounds.
             #[inline(always)]
-            pub(crate) fn try_update<const SIZE: usize, T, F>(
+            pub(crate) fn try_update<T, I, F>(
                 io: &T,
                 idx: usize,
                 f: F,
             ) -> ::kernel::error::Result where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 F: ::core::ops::FnOnce(Self) -> Self,
             {
                 if idx < Self::SIZE {
@@ -593,13 +605,14 @@ impl $name {
             /// Read the array register at index `idx` from `io`, using the base address provided
             /// by `base` and adding the register's offset to it.
             #[inline(always)]
-            pub(crate) fn read<const SIZE: usize, T, B>(
+            pub(crate) fn read<T, I, B>(
                 io: &T,
                 #[allow(unused_variables)]
                 base: &B,
                 idx: usize,
             ) -> Self where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
             {
                 build_assert!(idx < Self::SIZE);
@@ -614,14 +627,15 @@ pub(crate) fn read<const SIZE: usize, T, B>(
             /// Write the value contained in `self` to `io`, using the base address provided by
             /// `base` and adding the offset of array register `idx` to it.
             #[inline(always)]
-            pub(crate) fn write<const SIZE: usize, T, B>(
+            pub(crate) fn write<T, I, B>(
                 self,
                 io: &T,
                 #[allow(unused_variables)]
                 base: &B,
                 idx: usize
             ) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
             {
                 build_assert!(idx < Self::SIZE);
@@ -636,13 +650,14 @@ pub(crate) fn write<const SIZE: usize, T, B>(
             /// by `base` and adding the register's offset to it, then run `f` on its value to
             /// obtain a new value to write back.
             #[inline(always)]
-            pub(crate) fn update<const SIZE: usize, T, B, F>(
+            pub(crate) fn update<T, I, B, F>(
                 io: &T,
                 base: &B,
                 idx: usize,
                 f: F,
             ) where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
                 F: ::core::ops::FnOnce(Self) -> Self,
             {
@@ -656,12 +671,13 @@ pub(crate) fn update<const SIZE: usize, T, B, F>(
             /// The validity of `idx` is checked at run-time, and `EINVAL` is returned is the
             /// access was out-of-bounds.
             #[inline(always)]
-            pub(crate) fn try_read<const SIZE: usize, T, B>(
+            pub(crate) fn try_read<T, I, B>(
                 io: &T,
                 base: &B,
                 idx: usize,
             ) -> ::kernel::error::Result<Self> where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
             {
                 if idx < Self::SIZE {
@@ -677,13 +693,14 @@ pub(crate) fn try_read<const SIZE: usize, T, B>(
             /// The validity of `idx` is checked at run-time, and `EINVAL` is returned is the
             /// access was out-of-bounds.
             #[inline(always)]
-            pub(crate) fn try_write<const SIZE: usize, T, B>(
+            pub(crate) fn try_write<T, I, B>(
                 self,
                 io: &T,
                 base: &B,
                 idx: usize,
             ) -> ::kernel::error::Result where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
             {
                 if idx < Self::SIZE {
@@ -700,13 +717,14 @@ pub(crate) fn try_write<const SIZE: usize, T, B>(
             /// The validity of `idx` is checked at run-time, and `EINVAL` is returned is the
             /// access was out-of-bounds.
             #[inline(always)]
-            pub(crate) fn try_update<const SIZE: usize, T, B, F>(
+            pub(crate) fn try_update<T, I, B, F>(
                 io: &T,
                 base: &B,
                 idx: usize,
                 f: F,
             ) -> ::kernel::error::Result where
-                T: ::core::ops::Deref<Target = ::kernel::io::Io<SIZE>>,
+                T: ::core::ops::Deref<Target = I>,
+                I: ::kernel::io::IoKnownSize + ::kernel::io::IoCapable<u32>,
                 B: crate::regs::macros::RegisterBase<$base>,
                 F: ::core::ops::FnOnce(Self) -> Self,
             {
diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
index abf423560ff4..fe33b519e4d8 100644
--- a/drivers/gpu/nova-core/vbios.rs
+++ b/drivers/gpu/nova-core/vbios.rs
@@ -6,6 +6,7 @@
 
 use kernel::{
     device,
+    io::Io,
     prelude::*,
     ptr::{
         Alignable,
diff --git a/drivers/pwm/pwm_th1520.rs b/drivers/pwm/pwm_th1520.rs
index e3b7e77356fc..616ca398b2c5 100644
--- a/drivers/pwm/pwm_th1520.rs
+++ b/drivers/pwm/pwm_th1520.rs
@@ -26,7 +26,10 @@
     clk::Clk,
     device::{Bound, Core, Device},
     devres,
-    io::mem::IoMem,
+    io::{
+        mem::IoMem,
+        Io, //
+    },
     of, platform,
     prelude::*,
     pwm, time,
diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index 43089511bf76..cdc49677022a 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -74,14 +74,17 @@ struct Inner<T: Send> {
 ///     devres::Devres,
 ///     io::{
 ///         Io,
-///         IoRaw,
-///         PhysAddr,
+///         IoKnownSize,
+///         Mmio,
+///         MmioRaw,
+///         PhysAddr, //
 ///     },
+///     prelude::*,
 /// };
 /// use core::ops::Deref;
 ///
 /// // See also [`pci::Bar`] for a real example.
-/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
+/// struct IoMem<const SIZE: usize>(MmioRaw<SIZE>);
 ///
 /// impl<const SIZE: usize> IoMem<SIZE> {
 ///     /// # Safety
@@ -96,7 +99,7 @@ struct Inner<T: Send> {
 ///             return Err(ENOMEM);
 ///         }
 ///
-///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
+///         Ok(IoMem(MmioRaw::new(addr as usize, SIZE)?))
 ///     }
 /// }
 ///
@@ -108,11 +111,11 @@ struct Inner<T: Send> {
 /// }
 ///
 /// impl<const SIZE: usize> Deref for IoMem<SIZE> {
-///    type Target = Io<SIZE>;
+///    type Target = Mmio<SIZE>;
 ///
 ///    fn deref(&self) -> &Self::Target {
 ///         // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
-///         unsafe { Io::from_raw(&self.0) }
+///         unsafe { Mmio::from_raw(&self.0) }
 ///    }
 /// }
 /// # fn no_run(dev: &Device<Bound>) -> Result<(), Error> {
@@ -258,6 +261,10 @@ pub fn device(&self) -> &Device {
     /// use kernel::{
     ///     device::Core,
     ///     devres::Devres,
+    ///     io::{
+    ///         Io,
+    ///         IoKnownSize, //
+    ///     },
     ///     pci, //
     /// };
     ///
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index a97eb44a9a87..152afdcbaf78 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -32,16 +32,16 @@
 /// By itself, the existence of an instance of this structure does not provide any guarantees that
 /// the represented MMIO region does exist or is properly mapped.
 ///
-/// Instead, the bus specific MMIO implementation must convert this raw representation into an `Io`
-/// instance providing the actual memory accessors. Only by the conversion into an `Io` structure
-/// any guarantees are given.
-pub struct IoRaw<const SIZE: usize = 0> {
+/// Instead, the bus specific MMIO implementation must convert this raw representation into an
+/// `Mmio` instance providing the actual memory accessors. Only by the conversion into an `Mmio`
+/// structure any guarantees are given.
+pub struct MmioRaw<const SIZE: usize = 0> {
     addr: usize,
     maxsize: usize,
 }
 
-impl<const SIZE: usize> IoRaw<SIZE> {
-    /// Returns a new `IoRaw` instance on success, an error otherwise.
+impl<const SIZE: usize> MmioRaw<SIZE> {
+    /// Returns a new `MmioRaw` instance on success, an error otherwise.
     pub fn new(addr: usize, maxsize: usize) -> Result<Self> {
         if maxsize < SIZE {
             return Err(EINVAL);
@@ -81,14 +81,16 @@ pub fn maxsize(&self) -> usize {
 ///     ffi::c_void,
 ///     io::{
 ///         Io,
-///         IoRaw,
+///         IoKnownSize,
+///         Mmio,
+///         MmioRaw,
 ///         PhysAddr,
 ///     },
 /// };
 /// use core::ops::Deref;
 ///
 /// // See also `pci::Bar` for a real example.
-/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
+/// struct IoMem<const SIZE: usize>(MmioRaw<SIZE>);
 ///
 /// impl<const SIZE: usize> IoMem<SIZE> {
 ///     /// # Safety
@@ -103,7 +105,7 @@ pub fn maxsize(&self) -> usize {
 ///             return Err(ENOMEM);
 ///         }
 ///
-///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
+///         Ok(IoMem(MmioRaw::new(addr as usize, SIZE)?))
 ///     }
 /// }
 ///
@@ -115,11 +117,11 @@ pub fn maxsize(&self) -> usize {
 /// }
 ///
 /// impl<const SIZE: usize> Deref for IoMem<SIZE> {
-///    type Target = Io<SIZE>;
+///    type Target = Mmio<SIZE>;
 ///
 ///    fn deref(&self) -> &Self::Target {
 ///         // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
-///         unsafe { Io::from_raw(&self.0) }
+///         unsafe { Mmio::from_raw(&self.0) }
 ///    }
 /// }
 ///
@@ -133,29 +135,31 @@ pub fn maxsize(&self) -> usize {
 /// # }
 /// ```
 #[repr(transparent)]
-pub struct Io<const SIZE: usize = 0>(IoRaw<SIZE>);
+pub struct Mmio<const SIZE: usize = 0>(MmioRaw<SIZE>);
 
 macro_rules! define_read {
-    ($(#[$attr:meta])* $name:ident, $try_name:ident, $c_fn:ident -> $type_name:ty) => {
+    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident -> $type_name:ty) => {
         /// Read IO data from a given offset known at compile time.
         ///
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
         /// time, the build will fail.
         $(#[$attr])*
         #[inline]
-        pub fn $name(&self, offset: usize) -> $type_name {
+        $vis fn $name(&self, offset: usize) -> $type_name {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
             unsafe { bindings::$c_fn(addr as *const c_void) }
         }
+    };
 
+    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $c_fn:ident -> $type_name:ty) => {
         /// Read IO data from a given offset.
         ///
         /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
         /// out of bounds.
         $(#[$attr])*
-        pub fn $try_name(&self, offset: usize) -> Result<$type_name> {
+        $vis fn $try_name(&self, offset: usize) -> Result<$type_name> {
             let addr = self.io_addr::<$type_name>(offset)?;
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
@@ -163,74 +167,95 @@ pub fn $try_name(&self, offset: usize) -> Result<$type_name> {
         }
     };
 }
+pub(crate) use define_read;
 
 macro_rules! define_write {
-    ($(#[$attr:meta])* $name:ident, $try_name:ident, $c_fn:ident <- $type_name:ty) => {
+    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident <- $type_name:ty) => {
         /// Write IO data from a given offset known at compile time.
         ///
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
         /// time, the build will fail.
         $(#[$attr])*
         #[inline]
-        pub fn $name(&self, value: $type_name, offset: usize) {
+        $vis fn $name(&self, value: $type_name, offset: usize) {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
             unsafe { bindings::$c_fn(value, addr as *mut c_void) }
         }
+    };
 
+    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $c_fn:ident <- $type_name:ty) => {
         /// Write IO data from a given offset.
         ///
         /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
         /// out of bounds.
         $(#[$attr])*
-        pub fn $try_name(&self, value: $type_name, offset: usize) -> Result {
+        $vis fn $try_name(&self, value: $type_name, offset: usize) -> Result {
             let addr = self.io_addr::<$type_name>(offset)?;
 
             // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            unsafe { bindings::$c_fn(value, addr as *mut c_void) }
+            unsafe { bindings::$c_fn(value, addr as *mut c_void) };
             Ok(())
         }
     };
 }
-
-impl<const SIZE: usize> Io<SIZE> {
-    /// Converts an `IoRaw` into an `Io` instance, providing the accessors to the MMIO mapping.
-    ///
-    /// # Safety
-    ///
-    /// Callers must ensure that `addr` is the start of a valid I/O mapped memory region of size
-    /// `maxsize`.
-    pub unsafe fn from_raw(raw: &IoRaw<SIZE>) -> &Self {
-        // SAFETY: `Io` is a transparent wrapper around `IoRaw`.
-        unsafe { &*core::ptr::from_ref(raw).cast() }
+pub(crate) use define_write;
+
+/// Checks whether an access of type `U` at the given `offset`
+/// is valid within this region.
+#[inline]
+const fn offset_valid<U>(offset: usize, size: usize) -> bool {
+    let type_size = core::mem::size_of::<U>();
+    if let Some(end) = offset.checked_add(type_size) {
+        end <= size && offset % type_size == 0
+    } else {
+        false
     }
+}
+
+/// Marker trait indicating that an I/O backend supports operations of a certain type.
+///
+/// Different I/O backends can implement this trait to expose only the operations they support.
+///
+/// For example, a PCI configuration space may implement `IoCapable<u8>`, `IoCapable<u16>`,
+/// and `IoCapable<u32>`, but not `IoCapable<u64>`, while an MMIO region on a 64-bit
+/// system might implement all four.
+pub trait IoCapable<T> {}
+
+/// Types implementing this trait (e.g. MMIO BARs or PCI config regions)
+/// can perform I/O operations on regions of memory.
+///
+/// This is an abstract representation to be implemented by arbitrary I/O
+/// backends (e.g. MMIO, PCI config space, etc.).
+///
+/// The [`Io`] trait provides:
+/// - Base address and size information
+/// - Helper methods for offset validation and address calculation
+/// - Fallible (runtime checked) accessors for different data widths
+///
+/// Which I/O methods are available depends on which [`IoCapable<T>`] traits
+/// are implemented for the type.
+///
+/// # Examples
+///
+/// For MMIO regions, all widths (u8, u16, u32, and u64 on 64-bit systems) are typically
+/// supported. For PCI configuration space, u8, u16, and u32 are supported but u64 is not.
+pub trait Io {
+    /// Minimum usable size of this region.
+    const MIN_SIZE: usize;
 
     /// Returns the base address of this mapping.
-    #[inline]
-    pub fn addr(&self) -> usize {
-        self.0.addr()
-    }
+    fn addr(&self) -> usize;
 
     /// Returns the maximum size of this mapping.
-    #[inline]
-    pub fn maxsize(&self) -> usize {
-        self.0.maxsize()
-    }
-
-    #[inline]
-    const fn offset_valid<U>(offset: usize, size: usize) -> bool {
-        let type_size = core::mem::size_of::<U>();
-        if let Some(end) = offset.checked_add(type_size) {
-            end <= size && offset % type_size == 0
-        } else {
-            false
-        }
-    }
+    fn maxsize(&self) -> usize;
 
+    /// Returns the absolute I/O address for a given `offset`,
+    /// performing runtime bound checks.
     #[inline]
     fn io_addr<U>(&self, offset: usize) -> Result<usize> {
-        if !Self::offset_valid::<U>(offset, self.maxsize()) {
+        if !offset_valid::<U>(offset, self.maxsize()) {
             return Err(EINVAL);
         }
 
@@ -239,50 +264,302 @@ fn io_addr<U>(&self, offset: usize) -> Result<usize> {
         self.addr().checked_add(offset).ok_or(EINVAL)
     }
 
+    /// Returns the absolute I/O address for a given `offset`,
+    /// performing compile-time bound checks.
     #[inline]
     fn io_addr_assert<U>(&self, offset: usize) -> usize {
-        build_assert!(Self::offset_valid::<U>(offset, SIZE));
+        build_assert!(offset_valid::<U>(offset, Self::MIN_SIZE));
 
         self.addr() + offset
     }
 
-    define_read!(read8, try_read8, readb -> u8);
-    define_read!(read16, try_read16, readw -> u16);
-    define_read!(read32, try_read32, readl -> u32);
+    /// Fallible 8-bit read with runtime bounds check.
+    #[inline(always)]
+    fn try_read8(&self, _offset: usize) -> Result<u8>
+    where
+        Self: IoCapable<u8>,
+    {
+        const { assert!(false, "Backend does not support fallible 8-bit read") };
+        unreachable!()
+    }
+
+    /// Fallible 16-bit read with runtime bounds check.
+    #[inline(always)]
+    fn try_read16(&self, _offset: usize) -> Result<u16>
+    where
+        Self: IoCapable<u16>,
+    {
+        const { assert!(false, "Backend does not support fallible 16-bit read") };
+        unreachable!()
+    }
+
+    /// Fallible 32-bit read with runtime bounds check.
+    #[inline(always)]
+    fn try_read32(&self, _offset: usize) -> Result<u32>
+    where
+        Self: IoCapable<u32>,
+    {
+        const { assert!(false, "Backend does not support fallible 32-bit read") };
+        unreachable!()
+    }
+
+    /// Fallible 64-bit read with runtime bounds check.
+    #[cfg(CONFIG_64BIT)]
+    #[inline(always)]
+    fn try_read64(&self, _offset: usize) -> Result<u64>
+    where
+        Self: IoCapable<u64>,
+    {
+        const { assert!(false, "Backend does not support fallible 64-bit read") };
+        unreachable!()
+    }
+
+    /// Fallible 8-bit write with runtime bounds check.
+    #[inline(always)]
+    fn try_write8(&self, _value: u8, _offset: usize) -> Result
+    where
+        Self: IoCapable<u8>,
+    {
+        const { assert!(false, "Backend does not support fallible 8-bit write") };
+        unreachable!()
+    }
+
+    /// Fallible 16-bit write with runtime bounds check.
+    #[inline(always)]
+    fn try_write16(&self, _value: u16, _offset: usize) -> Result
+    where
+        Self: IoCapable<u16>,
+    {
+        const { assert!(false, "Backend does not support fallible 16-bit write") };
+        unreachable!()
+    }
+
+    /// Fallible 32-bit write with runtime bounds check.
+    #[inline(always)]
+    fn try_write32(&self, _value: u32, _offset: usize) -> Result
+    where
+        Self: IoCapable<u32>,
+    {
+        const { assert!(false, "Backend does not support fallible 32-bit write") };
+        unreachable!()
+    }
+
+    /// Fallible 64-bit write with runtime bounds check.
+    #[cfg(CONFIG_64BIT)]
+    #[inline(always)]
+    fn try_write64(&self, _value: u64, _offset: usize) -> Result
+    where
+        Self: IoCapable<u64>,
+    {
+        const { assert!(false, "Backend does not support fallible 64-bit write") };
+        unreachable!()
+    }
+}
+
+/// Types with a known size at compile time can provide infallible I/O accessors.
+///
+/// This trait extends [`Io`] to provide compile-time bounds-checked I/O operations
+/// for regions where the size is known at compile time (e.g., `Mmio<SIZE>`).
+pub trait IoKnownSize: Io {
+    /// Infallible 8-bit read with compile-time bounds check.
+    #[inline(always)]
+    fn read8(&self, _offset: usize) -> u8
+    where
+        Self: IoCapable<u8>,
+    {
+        const { assert!(false, "Backend does not support infallible 8-bit read") };
+        unreachable!()
+    }
+
+    /// Infallible 16-bit read with compile-time bounds check.
+    #[inline(always)]
+    fn read16(&self, _offset: usize) -> u16
+    where
+        Self: IoCapable<u16>,
+    {
+        const { assert!(false, "Backend does not support infallible 16-bit read") };
+        unreachable!()
+    }
+
+    /// Infallible 32-bit read with compile-time bounds check.
+    #[inline(always)]
+    fn read32(&self, _offset: usize) -> u32
+    where
+        Self: IoCapable<u32>,
+    {
+        const { assert!(false, "Backend does not support infallible 32-bit read") };
+        unreachable!()
+    }
+
+    /// Infallible 64-bit read with compile-time bounds check.
+    #[cfg(CONFIG_64BIT)]
+    #[inline(always)]
+    fn read64(&self, _offset: usize) -> u64
+    where
+        Self: IoCapable<u64>,
+    {
+        const { assert!(false, "Backend does not support infallible 64-bit read") };
+        unreachable!()
+    }
+
+    /// Infallible 8-bit write with compile-time bounds check.
+    #[inline(always)]
+    fn write8(&self, _value: u8, _offset: usize)
+    where
+        Self: IoCapable<u8>,
+    {
+        const { assert!(false, "Backend does not support infallible 8-bit write") };
+        unreachable!()
+    }
+
+    /// Infallible 16-bit write with compile-time bounds check.
+    #[inline(always)]
+    fn write16(&self, _value: u16, _offset: usize)
+    where
+        Self: IoCapable<u16>,
+    {
+        const { assert!(false, "Backend does not support infallible 16-bit write") };
+        unreachable!()
+    }
+
+    /// Infallible 32-bit write with compile-time bounds check.
+    #[inline(always)]
+    fn write32(&self, _value: u32, _offset: usize)
+    where
+        Self: IoCapable<u32>,
+    {
+        const { assert!(false, "Backend does not support infallible 32-bit write") };
+        unreachable!()
+    }
+
+    /// Infallible 64-bit write with compile-time bounds check.
+    #[cfg(CONFIG_64BIT)]
+    #[inline(always)]
+    fn write64(&self, _value: u64, _offset: usize)
+    where
+        Self: IoCapable<u64>,
+    {
+        const { assert!(false, "Backend does not support infallible 64-bit write") };
+        unreachable!()
+    }
+}
+
+// MMIO regions support 8, 16, and 32-bit accesses.
+impl<const SIZE: usize> IoCapable<u8> for Mmio<SIZE> {}
+impl<const SIZE: usize> IoCapable<u16> for Mmio<SIZE> {}
+impl<const SIZE: usize> IoCapable<u32> for Mmio<SIZE> {}
+
+// MMIO regions on 64-bit systems also support 64-bit accesses.
+#[cfg(CONFIG_64BIT)]
+impl<const SIZE: usize> IoCapable<u64> for Mmio<SIZE> {}
+
+impl<const SIZE: usize> Io for Mmio<SIZE> {
+    const MIN_SIZE: usize = SIZE;
+
+    /// Returns the base address of this mapping.
+    #[inline]
+    fn addr(&self) -> usize {
+        self.0.addr()
+    }
+
+    /// Returns the maximum size of this mapping.
+    #[inline]
+    fn maxsize(&self) -> usize {
+        self.0.maxsize()
+    }
+
+    define_read!(fallible, try_read8, readb -> u8);
+    define_read!(fallible, try_read16, readw -> u16);
+    define_read!(fallible, try_read32, readl -> u32);
     define_read!(
+        fallible,
         #[cfg(CONFIG_64BIT)]
-        read64,
         try_read64,
         readq -> u64
     );
 
-    define_read!(read8_relaxed, try_read8_relaxed, readb_relaxed -> u8);
-    define_read!(read16_relaxed, try_read16_relaxed, readw_relaxed -> u16);
-    define_read!(read32_relaxed, try_read32_relaxed, readl_relaxed -> u32);
+    define_write!(fallible, try_write8, writeb <- u8);
+    define_write!(fallible, try_write16, writew <- u16);
+    define_write!(fallible, try_write32, writel <- u32);
+    define_write!(
+        fallible,
+        #[cfg(CONFIG_64BIT)]
+        try_write64,
+        writeq <- u64
+    );
+}
+
+impl<const SIZE: usize> IoKnownSize for Mmio<SIZE> {
+    define_read!(infallible, read8, readb -> u8);
+    define_read!(infallible, read16, readw -> u16);
+    define_read!(infallible, read32, readl -> u32);
     define_read!(
+        infallible,
         #[cfg(CONFIG_64BIT)]
-        read64_relaxed,
-        try_read64_relaxed,
-        readq_relaxed -> u64
+        read64,
+        readq -> u64
     );
 
-    define_write!(write8, try_write8, writeb <- u8);
-    define_write!(write16, try_write16, writew <- u16);
-    define_write!(write32, try_write32, writel <- u32);
+    define_write!(infallible, write8, writeb <- u8);
+    define_write!(infallible, write16, writew <- u16);
+    define_write!(infallible, write32, writel <- u32);
     define_write!(
+        infallible,
         #[cfg(CONFIG_64BIT)]
         write64,
-        try_write64,
         writeq <- u64
     );
+}
+
+impl<const SIZE: usize> Mmio<SIZE> {
+    /// Converts an `MmioRaw` into an `Mmio` instance, providing the accessors to the MMIO mapping.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that `addr` is the start of a valid I/O mapped memory region of size
+    /// `maxsize`.
+    pub unsafe fn from_raw(raw: &MmioRaw<SIZE>) -> &Self {
+        // SAFETY: `Mmio` is a transparent wrapper around `MmioRaw`.
+        unsafe { &*core::ptr::from_ref(raw).cast() }
+    }
+
+    define_read!(infallible, pub read8_relaxed, readb_relaxed -> u8);
+    define_read!(infallible, pub read16_relaxed, readw_relaxed -> u16);
+    define_read!(infallible, pub read32_relaxed, readl_relaxed -> u32);
+    define_read!(
+        infallible,
+        #[cfg(CONFIG_64BIT)]
+        pub read64_relaxed,
+        readq_relaxed -> u64
+    );
+
+    define_read!(fallible, pub try_read8_relaxed, readb_relaxed -> u8);
+    define_read!(fallible, pub try_read16_relaxed, readw_relaxed -> u16);
+    define_read!(fallible, pub try_read32_relaxed, readl_relaxed -> u32);
+    define_read!(
+        fallible,
+        #[cfg(CONFIG_64BIT)]
+        pub try_read64_relaxed,
+        readq_relaxed -> u64
+    );
+
+    define_write!(infallible, pub write8_relaxed, writeb_relaxed <- u8);
+    define_write!(infallible, pub write16_relaxed, writew_relaxed <- u16);
+    define_write!(infallible, pub write32_relaxed, writel_relaxed <- u32);
+    define_write!(
+        infallible,
+        #[cfg(CONFIG_64BIT)]
+        pub write64_relaxed,
+        writeq_relaxed <- u64
+    );
 
-    define_write!(write8_relaxed, try_write8_relaxed, writeb_relaxed <- u8);
-    define_write!(write16_relaxed, try_write16_relaxed, writew_relaxed <- u16);
-    define_write!(write32_relaxed, try_write32_relaxed, writel_relaxed <- u32);
+    define_write!(fallible, pub try_write8_relaxed, writeb_relaxed <- u8);
+    define_write!(fallible, pub try_write16_relaxed, writew_relaxed <- u16);
+    define_write!(fallible, pub try_write32_relaxed, writel_relaxed <- u32);
     define_write!(
+        fallible,
         #[cfg(CONFIG_64BIT)]
-        write64_relaxed,
-        try_write64_relaxed,
+        pub try_write64_relaxed,
         writeq_relaxed <- u64
     );
 }
diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
index e4878c131c6d..620022cff401 100644
--- a/rust/kernel/io/mem.rs
+++ b/rust/kernel/io/mem.rs
@@ -16,8 +16,8 @@
             Region,
             Resource, //
         },
-        Io,
-        IoRaw, //
+        Mmio,
+        MmioRaw, //
     },
     prelude::*,
 };
@@ -212,7 +212,7 @@ pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> +
 }
 
 impl<const SIZE: usize> Deref for ExclusiveIoMem<SIZE> {
-    type Target = Io<SIZE>;
+    type Target = Mmio<SIZE>;
 
     fn deref(&self) -> &Self::Target {
         &self.iomem
@@ -226,10 +226,10 @@ fn deref(&self) -> &Self::Target {
 ///
 /// # Invariants
 ///
-/// [`IoMem`] always holds an [`IoRaw`] instance that holds a valid pointer to the
+/// [`IoMem`] always holds an [`MmioRaw`] instance that holds a valid pointer to the
 /// start of the I/O memory mapped region.
 pub struct IoMem<const SIZE: usize = 0> {
-    io: IoRaw<SIZE>,
+    io: MmioRaw<SIZE>,
 }
 
 impl<const SIZE: usize> IoMem<SIZE> {
@@ -264,7 +264,7 @@ fn ioremap(resource: &Resource) -> Result<Self> {
             return Err(ENOMEM);
         }
 
-        let io = IoRaw::new(addr as usize, size)?;
+        let io = MmioRaw::new(addr as usize, size)?;
         let io = IoMem { io };
 
         Ok(io)
@@ -287,10 +287,10 @@ fn drop(&mut self) {
 }
 
 impl<const SIZE: usize> Deref for IoMem<SIZE> {
-    type Target = Io<SIZE>;
+    type Target = Mmio<SIZE>;
 
     fn deref(&self) -> &Self::Target {
         // SAFETY: Safe as by the invariant of `IoMem`.
-        unsafe { Io::from_raw(&self.io) }
+        unsafe { Mmio::from_raw(&self.io) }
     }
 }
diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
index b1a2570364f4..75d1b3e8596c 100644
--- a/rust/kernel/io/poll.rs
+++ b/rust/kernel/io/poll.rs
@@ -45,12 +45,16 @@
 /// # Examples
 ///
 /// ```no_run
-/// use kernel::io::{Io, poll::read_poll_timeout};
+/// use kernel::io::{
+///     Io,
+///     Mmio,
+///     poll::read_poll_timeout, //
+/// };
 /// use kernel::time::Delta;
 ///
 /// const HW_READY: u16 = 0x01;
 ///
-/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
+/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) -> Result {
 ///     read_poll_timeout(
 ///         // The `op` closure reads the value of a specific status register.
 ///         || io.try_read16(0x1000),
@@ -128,12 +132,16 @@ pub fn read_poll_timeout<Op, Cond, T>(
 /// # Examples
 ///
 /// ```no_run
-/// use kernel::io::{poll::read_poll_timeout_atomic, Io};
+/// use kernel::io::{
+///     Io,
+///     Mmio,
+///     poll::read_poll_timeout_atomic, //
+/// };
 /// use kernel::time::Delta;
 ///
 /// const HW_READY: u16 = 0x01;
 ///
-/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
+/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) -> Result {
 ///     read_poll_timeout_atomic(
 ///         // The `op` closure reads the value of a specific status register.
 ///         || io.try_read16(0x1000),
diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
index 70e3854e7d8d..e3377397666e 100644
--- a/rust/kernel/pci/io.rs
+++ b/rust/kernel/pci/io.rs
@@ -8,8 +8,8 @@
     device,
     devres::Devres,
     io::{
-        Io,
-        IoRaw, //
+        Mmio,
+        MmioRaw, //
     },
     prelude::*,
     sync::aref::ARef, //
@@ -27,7 +27,7 @@
 /// memory mapped PCI BAR and its size.
 pub struct Bar<const SIZE: usize = 0> {
     pdev: ARef<Device>,
-    io: IoRaw<SIZE>,
+    io: MmioRaw<SIZE>,
     num: i32,
 }
 
@@ -63,7 +63,7 @@ pub(super) fn new(pdev: &Device, num: u32, name: &CStr) -> Result<Self> {
             return Err(ENOMEM);
         }
 
-        let io = match IoRaw::new(ioptr, len as usize) {
+        let io = match MmioRaw::new(ioptr, len as usize) {
             Ok(io) => io,
             Err(err) => {
                 // SAFETY:
@@ -117,11 +117,11 @@ fn drop(&mut self) {
 }
 
 impl<const SIZE: usize> Deref for Bar<SIZE> {
-    type Target = Io<SIZE>;
+    type Target = Mmio<SIZE>;
 
     fn deref(&self) -> &Self::Target {
         // SAFETY: By the type invariant of `Self`, the MMIO range in `self.io` is properly mapped.
-        unsafe { Io::from_raw(&self.io) }
+        unsafe { Mmio::from_raw(&self.io) }
     }
 }
 
diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
index ef04c6401e6a..bfb053059667 100644
--- a/samples/rust/rust_driver_pci.rs
+++ b/samples/rust/rust_driver_pci.rs
@@ -7,6 +7,10 @@
 use kernel::{
     device::Core,
     devres::Devres,
+    io::{
+        Io,
+        IoKnownSize, //
+    },
     pci,
     prelude::*,
     sync::aref::ARef, //
-- 
2.51.0

Re: [PATCH v11 2/5] rust: io: separate generic I/O helpers from MMIO implementation

[Gary Guo]

On Wed Jan 21, 2026 at 2:23 PM GMT, Zhi Wang wrote:
> The previous Io<SIZE> type combined both the generic I/O access helpers
> and MMIO implementation details in a single struct. This coupling prevented
> reusing the I/O helpers for other backends, such as PCI configuration
> space.
>
> Establish a clean separation between the I/O interface and concrete backends
> by separating generic I/O helpers from MMIO implementation.
>
> Introduce a new trait hierarchy to handle different access capabilities:
>
> - IoCapable<T>: A marker trait indicating that a backend supports I/O
>   operations of a certain type (u8, u16, u32, or u64).
>
> - Io trait: Defines fallible I/O methods (try_read8, try_write8, etc.) with
>   runtime bounds checking.
>
> - IoKnownSize trait: Extends Io to define infallible I/O methods (read8,
>   write8, etc.) with compile-time bounds checking for regions where the
>   size is known at compile time.
>
> Move the MMIO-specific logic into a dedicated Mmio<SIZE> type that
> implements the Io and IoKnownSize traits. Rename IoRaw to MmioRaw and
> update consumers to use the new types.
>

Hi Zhi, thanks for doing the work. It looks much nicer now :)

Still, some comments below.

Best,
Gary

> Cc: Alexandre Courbot <acourbot@nvidia.com>
> Cc: Alice Ryhl <aliceryhl@google.com>
> Cc: Bjorn Helgaas <helgaas@kernel.org>
> Cc: Gary Guo <gary@garyguo.net>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> ---
>  drivers/gpu/drm/tyr/regs.rs            |   1 +
>  drivers/gpu/nova-core/gsp/sequencer.rs |   5 +-
>  drivers/gpu/nova-core/regs/macros.rs   |  90 +++---
>  drivers/gpu/nova-core/vbios.rs         |   1 +
>  drivers/pwm/pwm_th1520.rs              |   5 +-
>  rust/kernel/devres.rs                  |  19 +-
>  rust/kernel/io.rs                      | 415 +++++++++++++++++++++----
>  rust/kernel/io/mem.rs                  |  16 +-
>  rust/kernel/io/poll.rs                 |  16 +-
>  rust/kernel/pci/io.rs                  |  12 +-
>  samples/rust/rust_driver_pci.rs        |   4 +
>  11 files changed, 453 insertions(+), 131 deletions(-)
>
> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> index a97eb44a9a87..152afdcbaf78 100644
> --- a/rust/kernel/io.rs
> +++ b/rust/kernel/io.rs
> @@ -32,16 +32,16 @@
>  /// By itself, the existence of an instance of this structure does not provide any guarantees that
>  /// the represented MMIO region does exist or is properly mapped.
>  ///
> -/// Instead, the bus specific MMIO implementation must convert this raw representation into an `Io`
> -/// instance providing the actual memory accessors. Only by the conversion into an `Io` structure
> -/// any guarantees are given.
> -pub struct IoRaw<const SIZE: usize = 0> {
> +/// Instead, the bus specific MMIO implementation must convert this raw representation into an
> +/// `Mmio` instance providing the actual memory accessors. Only by the conversion into an `Mmio`
> +/// structure any guarantees are given.
> +pub struct MmioRaw<const SIZE: usize = 0> {
>      addr: usize,
>      maxsize: usize,
>  }
>  
> -impl<const SIZE: usize> IoRaw<SIZE> {
> -    /// Returns a new `IoRaw` instance on success, an error otherwise.
> +impl<const SIZE: usize> MmioRaw<SIZE> {
> +    /// Returns a new `MmioRaw` instance on success, an error otherwise.
>      pub fn new(addr: usize, maxsize: usize) -> Result<Self> {
>          if maxsize < SIZE {
>              return Err(EINVAL);
> @@ -81,14 +81,16 @@ pub fn maxsize(&self) -> usize {
>  ///     ffi::c_void,
>  ///     io::{
>  ///         Io,
> -///         IoRaw,
> +///         IoKnownSize,
> +///         Mmio,
> +///         MmioRaw,
>  ///         PhysAddr,
>  ///     },
>  /// };
>  /// use core::ops::Deref;
>  ///
>  /// // See also `pci::Bar` for a real example.
> -/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
> +/// struct IoMem<const SIZE: usize>(MmioRaw<SIZE>);
>  ///
>  /// impl<const SIZE: usize> IoMem<SIZE> {
>  ///     /// # Safety
> @@ -103,7 +105,7 @@ pub fn maxsize(&self) -> usize {
>  ///             return Err(ENOMEM);
>  ///         }
>  ///
> -///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
> +///         Ok(IoMem(MmioRaw::new(addr as usize, SIZE)?))
>  ///     }
>  /// }
>  ///
> @@ -115,11 +117,11 @@ pub fn maxsize(&self) -> usize {
>  /// }
>  ///
>  /// impl<const SIZE: usize> Deref for IoMem<SIZE> {
> -///    type Target = Io<SIZE>;
> +///    type Target = Mmio<SIZE>;
>  ///
>  ///    fn deref(&self) -> &Self::Target {
>  ///         // SAFETY: The memory range stored in `self` has been properly mapped in `Self::new`.
> -///         unsafe { Io::from_raw(&self.0) }
> +///         unsafe { Mmio::from_raw(&self.0) }
>  ///    }
>  /// }
>  ///
> @@ -133,29 +135,31 @@ pub fn maxsize(&self) -> usize {
>  /// # }
>  /// ```
>  #[repr(transparent)]
> -pub struct Io<const SIZE: usize = 0>(IoRaw<SIZE>);
> +pub struct Mmio<const SIZE: usize = 0>(MmioRaw<SIZE>);
>  
>  macro_rules! define_read {
> -    ($(#[$attr:meta])* $name:ident, $try_name:ident, $c_fn:ident -> $type_name:ty) => {
> +    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident -> $type_name:ty) => {
>          /// Read IO data from a given offset known at compile time.
>          ///
>          /// Bound checks are performed on compile time, hence if the offset is not known at compile
>          /// time, the build will fail.
>          $(#[$attr])*
>          #[inline]
> -        pub fn $name(&self, offset: usize) -> $type_name {
> +        $vis fn $name(&self, offset: usize) -> $type_name {
>              let addr = self.io_addr_assert::<$type_name>(offset);
>  
>              // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
>              unsafe { bindings::$c_fn(addr as *const c_void) }
>          }
> +    };
>  
> +    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $c_fn:ident -> $type_name:ty) => {
>          /// Read IO data from a given offset.
>          ///
>          /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
>          /// out of bounds.
>          $(#[$attr])*
> -        pub fn $try_name(&self, offset: usize) -> Result<$type_name> {
> +        $vis fn $try_name(&self, offset: usize) -> Result<$type_name> {
>              let addr = self.io_addr::<$type_name>(offset)?;
>  
>              // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
> @@ -163,74 +167,95 @@ pub fn $try_name(&self, offset: usize) -> Result<$type_name> {
>          }
>      };
>  }
> +pub(crate) use define_read;
>  
>  macro_rules! define_write {
> -    ($(#[$attr:meta])* $name:ident, $try_name:ident, $c_fn:ident <- $type_name:ty) => {
> +    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident <- $type_name:ty) => {
>          /// Write IO data from a given offset known at compile time.
>          ///
>          /// Bound checks are performed on compile time, hence if the offset is not known at compile
>          /// time, the build will fail.
>          $(#[$attr])*
>          #[inline]
> -        pub fn $name(&self, value: $type_name, offset: usize) {
> +        $vis fn $name(&self, value: $type_name, offset: usize) {
>              let addr = self.io_addr_assert::<$type_name>(offset);
>  
>              // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
>              unsafe { bindings::$c_fn(value, addr as *mut c_void) }
>          }
> +    };
>  
> +    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $c_fn:ident <- $type_name:ty) => {
>          /// Write IO data from a given offset.
>          ///
>          /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
>          /// out of bounds.
>          $(#[$attr])*
> -        pub fn $try_name(&self, value: $type_name, offset: usize) -> Result {
> +        $vis fn $try_name(&self, value: $type_name, offset: usize) -> Result {
>              let addr = self.io_addr::<$type_name>(offset)?;
>  
>              // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
> -            unsafe { bindings::$c_fn(value, addr as *mut c_void) }
> +            unsafe { bindings::$c_fn(value, addr as *mut c_void) };
>              Ok(())
>          }
>      };
>  }
> -
> -impl<const SIZE: usize> Io<SIZE> {
> -    /// Converts an `IoRaw` into an `Io` instance, providing the accessors to the MMIO mapping.
> -    ///
> -    /// # Safety
> -    ///
> -    /// Callers must ensure that `addr` is the start of a valid I/O mapped memory region of size
> -    /// `maxsize`.
> -    pub unsafe fn from_raw(raw: &IoRaw<SIZE>) -> &Self {
> -        // SAFETY: `Io` is a transparent wrapper around `IoRaw`.
> -        unsafe { &*core::ptr::from_ref(raw).cast() }
> +pub(crate) use define_write;
> +
> +/// Checks whether an access of type `U` at the given `offset`
> +/// is valid within this region.
> +#[inline]
> +const fn offset_valid<U>(offset: usize, size: usize) -> bool {
> +    let type_size = core::mem::size_of::<U>();
> +    if let Some(end) = offset.checked_add(type_size) {
> +        end <= size && offset % type_size == 0
> +    } else {
> +        false
>      }
> +}
> +
> +/// Marker trait indicating that an I/O backend supports operations of a certain type.
> +///
> +/// Different I/O backends can implement this trait to expose only the operations they support.
> +///
> +/// For example, a PCI configuration space may implement `IoCapable<u8>`, `IoCapable<u16>`,
> +/// and `IoCapable<u32>`, but not `IoCapable<u64>`, while an MMIO region on a 64-bit
> +/// system might implement all four.
> +pub trait IoCapable<T> {}
> +
> +/// Types implementing this trait (e.g. MMIO BARs or PCI config regions)
> +/// can perform I/O operations on regions of memory.
> +///
> +/// This is an abstract representation to be implemented by arbitrary I/O
> +/// backends (e.g. MMIO, PCI config space, etc.).
> +///
> +/// The [`Io`] trait provides:
> +/// - Base address and size information
> +/// - Helper methods for offset validation and address calculation
> +/// - Fallible (runtime checked) accessors for different data widths
> +///
> +/// Which I/O methods are available depends on which [`IoCapable<T>`] traits
> +/// are implemented for the type.
> +///
> +/// # Examples
> +///
> +/// For MMIO regions, all widths (u8, u16, u32, and u64 on 64-bit systems) are typically
> +/// supported. For PCI configuration space, u8, u16, and u32 are supported but u64 is not.
> +pub trait Io {
> +    /// Minimum usable size of this region.
> +    const MIN_SIZE: usize;
>  
>      /// Returns the base address of this mapping.
> -    #[inline]
> -    pub fn addr(&self) -> usize {
> -        self.0.addr()
> -    }
> +    fn addr(&self) -> usize;
>  
>      /// Returns the maximum size of this mapping.
> -    #[inline]
> -    pub fn maxsize(&self) -> usize {
> -        self.0.maxsize()
> -    }
> -
> -    #[inline]
> -    const fn offset_valid<U>(offset: usize, size: usize) -> bool {
> -        let type_size = core::mem::size_of::<U>();
> -        if let Some(end) = offset.checked_add(type_size) {
> -            end <= size && offset % type_size == 0
> -        } else {
> -            false
> -        }
> -    }
> +    fn maxsize(&self) -> usize;
>  
> +    /// Returns the absolute I/O address for a given `offset`,
> +    /// performing runtime bound checks.
>      #[inline]
>      fn io_addr<U>(&self, offset: usize) -> Result<usize> {
> -        if !Self::offset_valid::<U>(offset, self.maxsize()) {
> +        if !offset_valid::<U>(offset, self.maxsize()) {
>              return Err(EINVAL);
>          }
>  
> @@ -239,50 +264,302 @@ fn io_addr<U>(&self, offset: usize) -> Result<usize> {
>          self.addr().checked_add(offset).ok_or(EINVAL)
>      }
>  
> +    /// Returns the absolute I/O address for a given `offset`,
> +    /// performing compile-time bound checks.
>      #[inline]
>      fn io_addr_assert<U>(&self, offset: usize) -> usize {
> -        build_assert!(Self::offset_valid::<U>(offset, SIZE));
> +        build_assert!(offset_valid::<U>(offset, Self::MIN_SIZE));
>  
>          self.addr() + offset
>      }
>  
> -    define_read!(read8, try_read8, readb -> u8);
> -    define_read!(read16, try_read16, readw -> u16);
> -    define_read!(read32, try_read32, readl -> u32);
> +    /// Fallible 8-bit read with runtime bounds check.
> +    #[inline(always)]
> +    fn try_read8(&self, _offset: usize) -> Result<u8>
> +    where
> +        Self: IoCapable<u8>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 8-bit read") };
> +        unreachable!()

I think this is actually where `build_error!()` make sense. Similar to how we
use it for vtable methods that are not defined (and hence will be `None`).

This would eliminate `unreachable!()`.

> +    }
> +
> +    /// Fallible 16-bit read with runtime bounds check.
> +    #[inline(always)]
> +    fn try_read16(&self, _offset: usize) -> Result<u16>
> +    where
> +        Self: IoCapable<u16>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 16-bit read") };
> +        unreachable!()
> +    }
> +
> +    /// Fallible 32-bit read with runtime bounds check.
> +    #[inline(always)]
> +    fn try_read32(&self, _offset: usize) -> Result<u32>
> +    where
> +        Self: IoCapable<u32>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 32-bit read") };
> +        unreachable!()
> +    }
> +
> +    /// Fallible 64-bit read with runtime bounds check.
> +    #[cfg(CONFIG_64BIT)]
> +    #[inline(always)]
> +    fn try_read64(&self, _offset: usize) -> Result<u64>
> +    where
> +        Self: IoCapable<u64>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 64-bit read") };
> +        unreachable!()
> +    }
> +
> +    /// Fallible 8-bit write with runtime bounds check.
> +    #[inline(always)]
> +    fn try_write8(&self, _value: u8, _offset: usize) -> Result
> +    where
> +        Self: IoCapable<u8>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 8-bit write") };
> +        unreachable!()
> +    }
> +
> +    /// Fallible 16-bit write with runtime bounds check.
> +    #[inline(always)]
> +    fn try_write16(&self, _value: u16, _offset: usize) -> Result
> +    where
> +        Self: IoCapable<u16>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 16-bit write") };
> +        unreachable!()
> +    }
> +
> +    /// Fallible 32-bit write with runtime bounds check.
> +    #[inline(always)]
> +    fn try_write32(&self, _value: u32, _offset: usize) -> Result
> +    where
> +        Self: IoCapable<u32>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 32-bit write") };
> +        unreachable!()
> +    }
> +
> +    /// Fallible 64-bit write with runtime bounds check.
> +    #[cfg(CONFIG_64BIT)]

As Alice mentioned previously, the CONFIG_64BIT shouldn't need to exist on the trait.

The cfg on the impl is sufficient (there might be `Io` that provides 64-bit
access on 32-bit systems anyway).

> +    #[inline(always)]
> +    fn try_write64(&self, _value: u64, _offset: usize) -> Result
> +    where
> +        Self: IoCapable<u64>,
> +    {
> +        const { assert!(false, "Backend does not support fallible 64-bit write") };
> +        unreachable!()
> +    }
> +}
> +
> +/// Types with a known size at compile time can provide infallible I/O accessors.
> +///
> +/// This trait extends [`Io`] to provide compile-time bounds-checked I/O operations
> +/// for regions where the size is known at compile time (e.g., `Mmio<SIZE>`).
> +pub trait IoKnownSize: Io {
> +    /// Infallible 8-bit read with compile-time bounds check.
> +    #[inline(always)]
> +    fn read8(&self, _offset: usize) -> u8
> +    where
> +        Self: IoCapable<u8>,

I think these *can* be also on `Io` with `Self: IoKnownSize` bound, although in
practice I don't think it would matter.

> +    {
> +        const { assert!(false, "Backend does not support infallible 8-bit read") };
> +        unreachable!()
> +    }
> +
> +    /// Infallible 16-bit read with compile-time bounds check.
> +    #[inline(always)]
> +    fn read16(&self, _offset: usize) -> u16
> +    where
> +        Self: IoCapable<u16>,
> +    {
> +        const { assert!(false, "Backend does not support infallible 16-bit read") };
> +        unreachable!()
> +    }
> +
> +    /// Infallible 32-bit read with compile-time bounds check.
> +    #[inline(always)]
> +    fn read32(&self, _offset: usize) -> u32
> +    where
> +        Self: IoCapable<u32>,
> +    {
> +        const { assert!(false, "Backend does not support infallible 32-bit read") };
> +        unreachable!()
> +    }
> +
> +    /// Infallible 64-bit read with compile-time bounds check.
> +    #[cfg(CONFIG_64BIT)]
> +    #[inline(always)]
> +    fn read64(&self, _offset: usize) -> u64
> +    where
> +        Self: IoCapable<u64>,
> +    {
> +        const { assert!(false, "Backend does not support infallible 64-bit read") };
> +        unreachable!()
> +    }
> +
> +    /// Infallible 8-bit write with compile-time bounds check.
> +    #[inline(always)]
> +    fn write8(&self, _value: u8, _offset: usize)
> +    where
> +        Self: IoCapable<u8>,
> +    {
> +        const { assert!(false, "Backend does not support infallible 8-bit write") };
> +        unreachable!()
> +    }
> +
> +    /// Infallible 16-bit write with compile-time bounds check.
> +    #[inline(always)]
> +    fn write16(&self, _value: u16, _offset: usize)
> +    where
> +        Self: IoCapable<u16>,
> +    {
> +        const { assert!(false, "Backend does not support infallible 16-bit write") };
> +        unreachable!()
> +    }
> +
> +    /// Infallible 32-bit write with compile-time bounds check.
> +    #[inline(always)]
> +    fn write32(&self, _value: u32, _offset: usize)
> +    where
> +        Self: IoCapable<u32>,
> +    {
> +        const { assert!(false, "Backend does not support infallible 32-bit write") };
> +        unreachable!()
> +    }
> +
> +    /// Infallible 64-bit write with compile-time bounds check.
> +    #[cfg(CONFIG_64BIT)]
> +    #[inline(always)]
> +    fn write64(&self, _value: u64, _offset: usize)
> +    where
> +        Self: IoCapable<u64>,
> +    {
> +        const { assert!(false, "Backend does not support infallible 64-bit write") };
> +        unreachable!()
> +    }
> +}
> +
> +// MMIO regions support 8, 16, and 32-bit accesses.
> +impl<const SIZE: usize> IoCapable<u8> for Mmio<SIZE> {}
> +impl<const SIZE: usize> IoCapable<u16> for Mmio<SIZE> {}
> +impl<const SIZE: usize> IoCapable<u32> for Mmio<SIZE> {}
> +
> +// MMIO regions on 64-bit systems also support 64-bit accesses.
> +#[cfg(CONFIG_64BIT)]
> +impl<const SIZE: usize> IoCapable<u64> for Mmio<SIZE> {}
> +
> +impl<const SIZE: usize> Io for Mmio<SIZE> {
> +    const MIN_SIZE: usize = SIZE;
> +
> +    /// Returns the base address of this mapping.
> +    #[inline]
> +    fn addr(&self) -> usize {
> +        self.0.addr()
> +    }
> +
> +    /// Returns the maximum size of this mapping.
> +    #[inline]
> +    fn maxsize(&self) -> usize {
> +        self.0.maxsize()
> +    }
> +
> +    define_read!(fallible, try_read8, readb -> u8);
> +    define_read!(fallible, try_read16, readw -> u16);
> +    define_read!(fallible, try_read32, readl -> u32);
>      define_read!(
> +        fallible,
>          #[cfg(CONFIG_64BIT)]
> -        read64,
>          try_read64,
>          readq -> u64
>      );
>  
> -    define_read!(read8_relaxed, try_read8_relaxed, readb_relaxed -> u8);
> -    define_read!(read16_relaxed, try_read16_relaxed, readw_relaxed -> u16);
> -    define_read!(read32_relaxed, try_read32_relaxed, readl_relaxed -> u32);
> +    define_write!(fallible, try_write8, writeb <- u8);
> +    define_write!(fallible, try_write16, writew <- u16);
> +    define_write!(fallible, try_write32, writel <- u32);
> +    define_write!(
> +        fallible,
> +        #[cfg(CONFIG_64BIT)]
> +        try_write64,
> +        writeq <- u64
> +    );
> +}
> +
> +impl<const SIZE: usize> IoKnownSize for Mmio<SIZE> {
> +    define_read!(infallible, read8, readb -> u8);
> +    define_read!(infallible, read16, readw -> u16);
> +    define_read!(infallible, read32, readl -> u32);
>      define_read!(
> +        infallible,
>          #[cfg(CONFIG_64BIT)]
> -        read64_relaxed,
> -        try_read64_relaxed,
> -        readq_relaxed -> u64
> +        read64,
> +        readq -> u64
>      );
>  
> -    define_write!(write8, try_write8, writeb <- u8);
> -    define_write!(write16, try_write16, writew <- u16);
> -    define_write!(write32, try_write32, writel <- u32);
> +    define_write!(infallible, write8, writeb <- u8);
> +    define_write!(infallible, write16, writew <- u16);
> +    define_write!(infallible, write32, writel <- u32);
>      define_write!(
> +        infallible,
>          #[cfg(CONFIG_64BIT)]
>          write64,
> -        try_write64,
>          writeq <- u64
>      );
> +}
> +
> +impl<const SIZE: usize> Mmio<SIZE> {
> +    /// Converts an `MmioRaw` into an `Mmio` instance, providing the accessors to the MMIO mapping.
> +    ///
> +    /// # Safety
> +    ///
> +    /// Callers must ensure that `addr` is the start of a valid I/O mapped memory region of size
> +    /// `maxsize`.
> +    pub unsafe fn from_raw(raw: &MmioRaw<SIZE>) -> &Self {
> +        // SAFETY: `Mmio` is a transparent wrapper around `MmioRaw`.
> +        unsafe { &*core::ptr::from_ref(raw).cast() }
> +    }
> +
> +    define_read!(infallible, pub read8_relaxed, readb_relaxed -> u8);
> +    define_read!(infallible, pub read16_relaxed, readw_relaxed -> u16);
> +    define_read!(infallible, pub read32_relaxed, readl_relaxed -> u32);
> +    define_read!(
> +        infallible,
> +        #[cfg(CONFIG_64BIT)]
> +        pub read64_relaxed,
> +        readq_relaxed -> u64
> +    );
> +
> +    define_read!(fallible, pub try_read8_relaxed, readb_relaxed -> u8);
> +    define_read!(fallible, pub try_read16_relaxed, readw_relaxed -> u16);
> +    define_read!(fallible, pub try_read32_relaxed, readl_relaxed -> u32);
> +    define_read!(
> +        fallible,
> +        #[cfg(CONFIG_64BIT)]
> +        pub try_read64_relaxed,
> +        readq_relaxed -> u64
> +    );
> +
> +    define_write!(infallible, pub write8_relaxed, writeb_relaxed <- u8);
> +    define_write!(infallible, pub write16_relaxed, writew_relaxed <- u16);
> +    define_write!(infallible, pub write32_relaxed, writel_relaxed <- u32);
> +    define_write!(
> +        infallible,
> +        #[cfg(CONFIG_64BIT)]
> +        pub write64_relaxed,
> +        writeq_relaxed <- u64
> +    );
>  
> -    define_write!(write8_relaxed, try_write8_relaxed, writeb_relaxed <- u8);
> -    define_write!(write16_relaxed, try_write16_relaxed, writew_relaxed <- u16);
> -    define_write!(write32_relaxed, try_write32_relaxed, writel_relaxed <- u32);
> +    define_write!(fallible, pub try_write8_relaxed, writeb_relaxed <- u8);
> +    define_write!(fallible, pub try_write16_relaxed, writew_relaxed <- u16);
> +    define_write!(fallible, pub try_write32_relaxed, writel_relaxed <- u32);
>      define_write!(
> +        fallible,
>          #[cfg(CONFIG_64BIT)]
> -        write64_relaxed,
> -        try_write64_relaxed,
> +        pub try_write64_relaxed,
>          writeq_relaxed <- u64
>      );
>  }
> diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
> index e4878c131c6d..620022cff401 100644
> --- a/rust/kernel/io/mem.rs
> +++ b/rust/kernel/io/mem.rs
> @@ -16,8 +16,8 @@
>              Region,
>              Resource, //
>          },
> -        Io,
> -        IoRaw, //
> +        Mmio,
> +        MmioRaw, //
>      },
>      prelude::*,
>  };
> @@ -212,7 +212,7 @@ pub fn new<'a>(io_request: IoRequest<'a>) -> impl PinInit<Devres<Self>, Error> +
>  }
>  
>  impl<const SIZE: usize> Deref for ExclusiveIoMem<SIZE> {
> -    type Target = Io<SIZE>;
> +    type Target = Mmio<SIZE>;
>  
>      fn deref(&self) -> &Self::Target {
>          &self.iomem
> @@ -226,10 +226,10 @@ fn deref(&self) -> &Self::Target {
>  ///
>  /// # Invariants
>  ///
> -/// [`IoMem`] always holds an [`IoRaw`] instance that holds a valid pointer to the
> +/// [`IoMem`] always holds an [`MmioRaw`] instance that holds a valid pointer to the
>  /// start of the I/O memory mapped region.
>  pub struct IoMem<const SIZE: usize = 0> {
> -    io: IoRaw<SIZE>,
> +    io: MmioRaw<SIZE>,
>  }
>  
>  impl<const SIZE: usize> IoMem<SIZE> {
> @@ -264,7 +264,7 @@ fn ioremap(resource: &Resource) -> Result<Self> {
>              return Err(ENOMEM);
>          }
>  
> -        let io = IoRaw::new(addr as usize, size)?;
> +        let io = MmioRaw::new(addr as usize, size)?;
>          let io = IoMem { io };
>  
>          Ok(io)
> @@ -287,10 +287,10 @@ fn drop(&mut self) {
>  }
>  
>  impl<const SIZE: usize> Deref for IoMem<SIZE> {
> -    type Target = Io<SIZE>;
> +    type Target = Mmio<SIZE>;
>  
>      fn deref(&self) -> &Self::Target {
>          // SAFETY: Safe as by the invariant of `IoMem`.
> -        unsafe { Io::from_raw(&self.io) }
> +        unsafe { Mmio::from_raw(&self.io) }
>      }
>  }
> diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
> index b1a2570364f4..75d1b3e8596c 100644
> --- a/rust/kernel/io/poll.rs
> +++ b/rust/kernel/io/poll.rs
> @@ -45,12 +45,16 @@
>  /// # Examples
>  ///
>  /// ```no_run
> -/// use kernel::io::{Io, poll::read_poll_timeout};
> +/// use kernel::io::{
> +///     Io,
> +///     Mmio,
> +///     poll::read_poll_timeout, //
> +/// };
>  /// use kernel::time::Delta;
>  ///
>  /// const HW_READY: u16 = 0x01;
>  ///
> -/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
> +/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) -> Result {
>  ///     read_poll_timeout(
>  ///         // The `op` closure reads the value of a specific status register.
>  ///         || io.try_read16(0x1000),
> @@ -128,12 +132,16 @@ pub fn read_poll_timeout<Op, Cond, T>(
>  /// # Examples
>  ///
>  /// ```no_run
> -/// use kernel::io::{poll::read_poll_timeout_atomic, Io};
> +/// use kernel::io::{
> +///     Io,
> +///     Mmio,
> +///     poll::read_poll_timeout_atomic, //
> +/// };
>  /// use kernel::time::Delta;
>  ///
>  /// const HW_READY: u16 = 0x01;
>  ///
> -/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
> +/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) -> Result {
>  ///     read_poll_timeout_atomic(
>  ///         // The `op` closure reads the value of a specific status register.
>  ///         || io.try_read16(0x1000),
> diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
> index 70e3854e7d8d..e3377397666e 100644
> --- a/rust/kernel/pci/io.rs
> +++ b/rust/kernel/pci/io.rs
> @@ -8,8 +8,8 @@
>      device,
>      devres::Devres,
>      io::{
> -        Io,
> -        IoRaw, //
> +        Mmio,
> +        MmioRaw, //
>      },
>      prelude::*,
>      sync::aref::ARef, //
> @@ -27,7 +27,7 @@
>  /// memory mapped PCI BAR and its size.
>  pub struct Bar<const SIZE: usize = 0> {
>      pdev: ARef<Device>,
> -    io: IoRaw<SIZE>,
> +    io: MmioRaw<SIZE>,
>      num: i32,
>  }
>  
> @@ -63,7 +63,7 @@ pub(super) fn new(pdev: &Device, num: u32, name: &CStr) -> Result<Self> {
>              return Err(ENOMEM);
>          }
>  
> -        let io = match IoRaw::new(ioptr, len as usize) {
> +        let io = match MmioRaw::new(ioptr, len as usize) {
>              Ok(io) => io,
>              Err(err) => {
>                  // SAFETY:
> @@ -117,11 +117,11 @@ fn drop(&mut self) {
>  }
>  
>  impl<const SIZE: usize> Deref for Bar<SIZE> {
> -    type Target = Io<SIZE>;
> +    type Target = Mmio<SIZE>;
>  
>      fn deref(&self) -> &Self::Target {
>          // SAFETY: By the type invariant of `Self`, the MMIO range in `self.io` is properly mapped.
> -        unsafe { Io::from_raw(&self.io) }
> +        unsafe { Mmio::from_raw(&self.io) }
>      }
>  }
>  
> diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
> index ef04c6401e6a..bfb053059667 100644
> --- a/samples/rust/rust_driver_pci.rs
> +++ b/samples/rust/rust_driver_pci.rs
> @@ -7,6 +7,10 @@
>  use kernel::{
>      device::Core,
>      devres::Devres,
> +    io::{
> +        Io,
> +        IoKnownSize, //
> +    },
>      pci,
>      prelude::*,
>      sync::aref::ARef, //

Re: [PATCH v11 2/5] rust: io: separate generic I/O helpers from MMIO implementation

[Zhi Wang]

On Wed, 21 Jan 2026 15:10:25 +0000
"Gary Guo" <gary@garyguo.net> wrote:

> On Wed Jan 21, 2026 at 2:23 PM GMT, Zhi Wang wrote:
> > The previous Io<SIZE> type combined both the generic I/O access helpers
> > and MMIO implementation details in a single struct. This coupling
> > prevented reusing the I/O helpers for other backends, such as PCI
> > configuration space.
> >
> > Establish a clean separation between the I/O interface and concrete
> > backends by separating generic I/O helpers from MMIO implementation.
> >
> > Introduce a new trait hierarchy to handle different access
> > capabilities:
> >
> > - IoCapable<T>: A marker trait indicating that a backend supports I/O
> >   operations of a certain type (u8, u16, u32, or u64).
> >
> > - Io trait: Defines fallible I/O methods (try_read8, try_write8, etc.)
> > with runtime bounds checking.
> >
> > - IoKnownSize trait: Extends Io to define infallible I/O methods
> > (read8, write8, etc.) with compile-time bounds checking for regions
> > where the size is known at compile time.
> >
> > Move the MMIO-specific logic into a dedicated Mmio<SIZE> type that
> > implements the Io and IoKnownSize traits. Rename IoRaw to MmioRaw and
> > update consumers to use the new types.
> >
> 
> Hi Zhi, thanks for doing the work. It looks much nicer now :)
> 

Hey Gary. Glad to see that. :) Will address them in the next re-spin.

> Still, some comments below.
> 
> Best,
> Gary
> 
> > Cc: Alexandre Courbot <acourbot@nvidia.com>
> > Cc: Alice Ryhl <aliceryhl@google.com>
> > Cc: Bjorn Helgaas <helgaas@kernel.org>
> > Cc: Gary Guo <gary@garyguo.net>
> > Cc: Danilo Krummrich <dakr@kernel.org>
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> > ---
> >  drivers/gpu/drm/tyr/regs.rs            |   1 +
> >  drivers/gpu/nova-core/gsp/sequencer.rs |   5 +-
> >  drivers/gpu/nova-core/regs/macros.rs   |  90 +++---
> >  drivers/gpu/nova-core/vbios.rs         |   1 +
> >  drivers/pwm/pwm_th1520.rs              |   5 +-
> >  rust/kernel/devres.rs                  |  19 +-
> >  rust/kernel/io.rs                      | 415 +++++++++++++++++++++----
> >  rust/kernel/io/mem.rs                  |  16 +-
> >  rust/kernel/io/poll.rs                 |  16 +-
> >  rust/kernel/pci/io.rs                  |  12 +-
> >  samples/rust/rust_driver_pci.rs        |   4 +
> >  11 files changed, 453 insertions(+), 131 deletions(-)
> >
> > diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> > index a97eb44a9a87..152afdcbaf78 100644
> > --- a/rust/kernel/io.rs
> > +++ b/rust/kernel/io.rs
> > @@ -32,16 +32,16 @@
> >  /// By itself, the existence of an instance of this structure does
> > not provide any guarantees that /// the represented MMIO region does
> > exist or is properly mapped. ///
> > -/// Instead, the bus specific MMIO implementation must convert this
> > raw representation into an `Io` -/// instance providing the actual
> > memory accessors. Only by the conversion into an `Io` structure -///
> > any guarantees are given. -pub struct IoRaw<const SIZE: usize = 0> {
> > +/// Instead, the bus specific MMIO implementation must convert this
> > raw representation into an +/// `Mmio` instance providing the actual
> > memory accessors. Only by the conversion into an `Mmio` +/// structure
> > any guarantees are given. +pub struct MmioRaw<const SIZE: usize = 0> {
> >      addr: usize,
> >      maxsize: usize,
> >  }
> >  
> > -impl<const SIZE: usize> IoRaw<SIZE> {
> > -    /// Returns a new `IoRaw` instance on success, an error otherwise.
> > +impl<const SIZE: usize> MmioRaw<SIZE> {
> > +    /// Returns a new `MmioRaw` instance on success, an error
> > otherwise. pub fn new(addr: usize, maxsize: usize) -> Result<Self> {
> >          if maxsize < SIZE {
> >              return Err(EINVAL);
> > @@ -81,14 +81,16 @@ pub fn maxsize(&self) -> usize {
> >  ///     ffi::c_void,
> >  ///     io::{
> >  ///         Io,
> > -///         IoRaw,
> > +///         IoKnownSize,
> > +///         Mmio,
> > +///         MmioRaw,
> >  ///         PhysAddr,
> >  ///     },
> >  /// };
> >  /// use core::ops::Deref;
> >  ///
> >  /// // See also `pci::Bar` for a real example.
> > -/// struct IoMem<const SIZE: usize>(IoRaw<SIZE>);
> > +/// struct IoMem<const SIZE: usize>(MmioRaw<SIZE>);
> >  ///
> >  /// impl<const SIZE: usize> IoMem<SIZE> {
> >  ///     /// # Safety
> > @@ -103,7 +105,7 @@ pub fn maxsize(&self) -> usize {
> >  ///             return Err(ENOMEM);
> >  ///         }
> >  ///
> > -///         Ok(IoMem(IoRaw::new(addr as usize, SIZE)?))
> > +///         Ok(IoMem(MmioRaw::new(addr as usize, SIZE)?))
> >  ///     }
> >  /// }
> >  ///
> > @@ -115,11 +117,11 @@ pub fn maxsize(&self) -> usize {
> >  /// }
> >  ///
> >  /// impl<const SIZE: usize> Deref for IoMem<SIZE> {
> > -///    type Target = Io<SIZE>;
> > +///    type Target = Mmio<SIZE>;
> >  ///
> >  ///    fn deref(&self) -> &Self::Target {
> >  ///         // SAFETY: The memory range stored in `self` has been
> > properly mapped in `Self::new`. -///         unsafe {
> > Io::from_raw(&self.0) } +///         unsafe { Mmio::from_raw(&self.0) }
> >  ///    }
> >  /// }
> >  ///
> > @@ -133,29 +135,31 @@ pub fn maxsize(&self) -> usize {
> >  /// # }
> >  /// ```
> >  #[repr(transparent)]
> > -pub struct Io<const SIZE: usize = 0>(IoRaw<SIZE>);
> > +pub struct Mmio<const SIZE: usize = 0>(MmioRaw<SIZE>);
> >  
> >  macro_rules! define_read {
> > -    ($(#[$attr:meta])* $name:ident, $try_name:ident, $c_fn:ident ->
> > $type_name:ty) => {
> > +    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident
> > -> $type_name:ty) => { /// Read IO data from a given offset known at
> > compile time. ///
> >          /// Bound checks are performed on compile time, hence if the
> > offset is not known at compile /// time, the build will fail.
> >          $(#[$attr])*
> >          #[inline]
> > -        pub fn $name(&self, offset: usize) -> $type_name {
> > +        $vis fn $name(&self, offset: usize) -> $type_name {
> >              let addr = self.io_addr_assert::<$type_name>(offset);
> >  
> >              // SAFETY: By the type invariant `addr` is a valid
> > address for MMIO operations. unsafe { bindings::$c_fn(addr as *const
> > c_void) } }
> > +    };
> >  
> > +    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident,
> > $c_fn:ident -> $type_name:ty) => { /// Read IO data from a given
> > offset. ///
> >          /// Bound checks are performed on runtime, it fails if the
> > offset (plus the type size) is /// out of bounds.
> >          $(#[$attr])*
> > -        pub fn $try_name(&self, offset: usize) -> Result<$type_name> {
> > +        $vis fn $try_name(&self, offset: usize) -> Result<$type_name>
> > { let addr = self.io_addr::<$type_name>(offset)?;
> >  
> >              // SAFETY: By the type invariant `addr` is a valid
> > address for MMIO operations. @@ -163,74 +167,95 @@ pub fn
> > $try_name(&self, offset: usize) -> Result<$type_name> { }
> >      };
> >  }
> > +pub(crate) use define_read;
> >  
> >  macro_rules! define_write {
> > -    ($(#[$attr:meta])* $name:ident, $try_name:ident, $c_fn:ident <-
> > $type_name:ty) => {
> > +    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident
> > <- $type_name:ty) => { /// Write IO data from a given offset known at
> > compile time. ///
> >          /// Bound checks are performed on compile time, hence if the
> > offset is not known at compile /// time, the build will fail.
> >          $(#[$attr])*
> >          #[inline]
> > -        pub fn $name(&self, value: $type_name, offset: usize) {
> > +        $vis fn $name(&self, value: $type_name, offset: usize) {
> >              let addr = self.io_addr_assert::<$type_name>(offset);
> >  
> >              // SAFETY: By the type invariant `addr` is a valid
> > address for MMIO operations. unsafe { bindings::$c_fn(value, addr as
> > *mut c_void) } }
> > +    };
> >  
> > +    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident,
> > $c_fn:ident <- $type_name:ty) => { /// Write IO data from a given
> > offset. ///
> >          /// Bound checks are performed on runtime, it fails if the
> > offset (plus the type size) is /// out of bounds.
> >          $(#[$attr])*
> > -        pub fn $try_name(&self, value: $type_name, offset: usize) ->
> > Result {
> > +        $vis fn $try_name(&self, value: $type_name, offset: usize) ->
> > Result { let addr = self.io_addr::<$type_name>(offset)?;
> >  
> >              // SAFETY: By the type invariant `addr` is a valid
> > address for MMIO operations.
> > -            unsafe { bindings::$c_fn(value, addr as *mut c_void) }
> > +            unsafe { bindings::$c_fn(value, addr as *mut c_void) };
> >              Ok(())
> >          }
> >      };
> >  }
> > -
> > -impl<const SIZE: usize> Io<SIZE> {
> > -    /// Converts an `IoRaw` into an `Io` instance, providing the
> > accessors to the MMIO mapping.
> > -    ///
> > -    /// # Safety
> > -    ///
> > -    /// Callers must ensure that `addr` is the start of a valid I/O
> > mapped memory region of size
> > -    /// `maxsize`.
> > -    pub unsafe fn from_raw(raw: &IoRaw<SIZE>) -> &Self {
> > -        // SAFETY: `Io` is a transparent wrapper around `IoRaw`.
> > -        unsafe { &*core::ptr::from_ref(raw).cast() }
> > +pub(crate) use define_write;
> > +
> > +/// Checks whether an access of type `U` at the given `offset`
> > +/// is valid within this region.
> > +#[inline]
> > +const fn offset_valid<U>(offset: usize, size: usize) -> bool {
> > +    let type_size = core::mem::size_of::<U>();
> > +    if let Some(end) = offset.checked_add(type_size) {
> > +        end <= size && offset % type_size == 0
> > +    } else {
> > +        false
> >      }
> > +}
> > +
> > +/// Marker trait indicating that an I/O backend supports operations
> > of a certain type. +///
> > +/// Different I/O backends can implement this trait to expose only
> > the operations they support. +///
> > +/// For example, a PCI configuration space may implement
> > `IoCapable<u8>`, `IoCapable<u16>`, +/// and `IoCapable<u32>`, but not
> > `IoCapable<u64>`, while an MMIO region on a 64-bit +/// system might
> > implement all four. +pub trait IoCapable<T> {}
> > +
> > +/// Types implementing this trait (e.g. MMIO BARs or PCI config
> > regions) +/// can perform I/O operations on regions of memory.
> > +///
> > +/// This is an abstract representation to be implemented by arbitrary
> > I/O +/// backends (e.g. MMIO, PCI config space, etc.).
> > +///
> > +/// The [`Io`] trait provides:
> > +/// - Base address and size information
> > +/// - Helper methods for offset validation and address calculation
> > +/// - Fallible (runtime checked) accessors for different data widths
> > +///
> > +/// Which I/O methods are available depends on which [`IoCapable<T>`]
> > traits +/// are implemented for the type.
> > +///
> > +/// # Examples
> > +///
> > +/// For MMIO regions, all widths (u8, u16, u32, and u64 on 64-bit
> > systems) are typically +/// supported. For PCI configuration space,
> > u8, u16, and u32 are supported but u64 is not. +pub trait Io {
> > +    /// Minimum usable size of this region.
> > +    const MIN_SIZE: usize;
> >  
> >      /// Returns the base address of this mapping.
> > -    #[inline]
> > -    pub fn addr(&self) -> usize {
> > -        self.0.addr()
> > -    }
> > +    fn addr(&self) -> usize;
> >  
> >      /// Returns the maximum size of this mapping.
> > -    #[inline]
> > -    pub fn maxsize(&self) -> usize {
> > -        self.0.maxsize()
> > -    }
> > -
> > -    #[inline]
> > -    const fn offset_valid<U>(offset: usize, size: usize) -> bool {
> > -        let type_size = core::mem::size_of::<U>();
> > -        if let Some(end) = offset.checked_add(type_size) {
> > -            end <= size && offset % type_size == 0
> > -        } else {
> > -            false
> > -        }
> > -    }
> > +    fn maxsize(&self) -> usize;
> >  
> > +    /// Returns the absolute I/O address for a given `offset`,
> > +    /// performing runtime bound checks.
> >      #[inline]
> >      fn io_addr<U>(&self, offset: usize) -> Result<usize> {
> > -        if !Self::offset_valid::<U>(offset, self.maxsize()) {
> > +        if !offset_valid::<U>(offset, self.maxsize()) {
> >              return Err(EINVAL);
> >          }
> >  
> > @@ -239,50 +264,302 @@ fn io_addr<U>(&self, offset: usize) ->
> > Result<usize> { self.addr().checked_add(offset).ok_or(EINVAL)
> >      }
> >  
> > +    /// Returns the absolute I/O address for a given `offset`,
> > +    /// performing compile-time bound checks.
> >      #[inline]
> >      fn io_addr_assert<U>(&self, offset: usize) -> usize {
> > -        build_assert!(Self::offset_valid::<U>(offset, SIZE));
> > +        build_assert!(offset_valid::<U>(offset, Self::MIN_SIZE));
> >  
> >          self.addr() + offset
> >      }
> >  
> > -    define_read!(read8, try_read8, readb -> u8);
> > -    define_read!(read16, try_read16, readw -> u16);
> > -    define_read!(read32, try_read32, readl -> u32);
> > +    /// Fallible 8-bit read with runtime bounds check.
> > +    #[inline(always)]
> > +    fn try_read8(&self, _offset: usize) -> Result<u8>
> > +    where
> > +        Self: IoCapable<u8>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 8-bit read") };
> > +        unreachable!()
> 
> I think this is actually where `build_error!()` make sense. Similar to
> how we use it for vtable methods that are not defined (and hence will be
> `None`).
> 
> This would eliminate `unreachable!()`.
> 
> > +    }
> > +
> > +    /// Fallible 16-bit read with runtime bounds check.
> > +    #[inline(always)]
> > +    fn try_read16(&self, _offset: usize) -> Result<u16>
> > +    where
> > +        Self: IoCapable<u16>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 16-bit read") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Fallible 32-bit read with runtime bounds check.
> > +    #[inline(always)]
> > +    fn try_read32(&self, _offset: usize) -> Result<u32>
> > +    where
> > +        Self: IoCapable<u32>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 32-bit read") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Fallible 64-bit read with runtime bounds check.
> > +    #[cfg(CONFIG_64BIT)]
> > +    #[inline(always)]
> > +    fn try_read64(&self, _offset: usize) -> Result<u64>
> > +    where
> > +        Self: IoCapable<u64>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 64-bit read") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Fallible 8-bit write with runtime bounds check.
> > +    #[inline(always)]
> > +    fn try_write8(&self, _value: u8, _offset: usize) -> Result
> > +    where
> > +        Self: IoCapable<u8>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 8-bit write") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Fallible 16-bit write with runtime bounds check.
> > +    #[inline(always)]
> > +    fn try_write16(&self, _value: u16, _offset: usize) -> Result
> > +    where
> > +        Self: IoCapable<u16>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 16-bit write") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Fallible 32-bit write with runtime bounds check.
> > +    #[inline(always)]
> > +    fn try_write32(&self, _value: u32, _offset: usize) -> Result
> > +    where
> > +        Self: IoCapable<u32>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 32-bit write") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Fallible 64-bit write with runtime bounds check.
> > +    #[cfg(CONFIG_64BIT)]
> 
> As Alice mentioned previously, the CONFIG_64BIT shouldn't need to exist
> on the trait.
> 
> The cfg on the impl is sufficient (there might be `Io` that provides
> 64-bit access on 32-bit systems anyway).
> 
> > +    #[inline(always)]
> > +    fn try_write64(&self, _value: u64, _offset: usize) -> Result
> > +    where
> > +        Self: IoCapable<u64>,
> > +    {
> > +        const { assert!(false, "Backend does not support fallible
> > 64-bit write") };
> > +        unreachable!()
> > +    }
> > +}
> > +
> > +/// Types with a known size at compile time can provide infallible
> > I/O accessors. +///
> > +/// This trait extends [`Io`] to provide compile-time bounds-checked
> > I/O operations +/// for regions where the size is known at compile
> > time (e.g., `Mmio<SIZE>`). +pub trait IoKnownSize: Io {
> > +    /// Infallible 8-bit read with compile-time bounds check.
> > +    #[inline(always)]
> > +    fn read8(&self, _offset: usize) -> u8
> > +    where
> > +        Self: IoCapable<u8>,
> 
> I think these *can* be also on `Io` with `Self: IoKnownSize` bound,
> although in practice I don't think it would matter.
> 
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 8-bit read") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Infallible 16-bit read with compile-time bounds check.
> > +    #[inline(always)]
> > +    fn read16(&self, _offset: usize) -> u16
> > +    where
> > +        Self: IoCapable<u16>,
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 16-bit read") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Infallible 32-bit read with compile-time bounds check.
> > +    #[inline(always)]
> > +    fn read32(&self, _offset: usize) -> u32
> > +    where
> > +        Self: IoCapable<u32>,
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 32-bit read") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Infallible 64-bit read with compile-time bounds check.
> > +    #[cfg(CONFIG_64BIT)]
> > +    #[inline(always)]
> > +    fn read64(&self, _offset: usize) -> u64
> > +    where
> > +        Self: IoCapable<u64>,
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 64-bit read") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Infallible 8-bit write with compile-time bounds check.
> > +    #[inline(always)]
> > +    fn write8(&self, _value: u8, _offset: usize)
> > +    where
> > +        Self: IoCapable<u8>,
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 8-bit write") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Infallible 16-bit write with compile-time bounds check.
> > +    #[inline(always)]
> > +    fn write16(&self, _value: u16, _offset: usize)
> > +    where
> > +        Self: IoCapable<u16>,
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 16-bit write") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Infallible 32-bit write with compile-time bounds check.
> > +    #[inline(always)]
> > +    fn write32(&self, _value: u32, _offset: usize)
> > +    where
> > +        Self: IoCapable<u32>,
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 32-bit write") };
> > +        unreachable!()
> > +    }
> > +
> > +    /// Infallible 64-bit write with compile-time bounds check.
> > +    #[cfg(CONFIG_64BIT)]
> > +    #[inline(always)]
> > +    fn write64(&self, _value: u64, _offset: usize)
> > +    where
> > +        Self: IoCapable<u64>,
> > +    {
> > +        const { assert!(false, "Backend does not support infallible
> > 64-bit write") };
> > +        unreachable!()
> > +    }
> > +}
> > +
> > +// MMIO regions support 8, 16, and 32-bit accesses.
> > +impl<const SIZE: usize> IoCapable<u8> for Mmio<SIZE> {}
> > +impl<const SIZE: usize> IoCapable<u16> for Mmio<SIZE> {}
> > +impl<const SIZE: usize> IoCapable<u32> for Mmio<SIZE> {}
> > +
> > +// MMIO regions on 64-bit systems also support 64-bit accesses.
> > +#[cfg(CONFIG_64BIT)]
> > +impl<const SIZE: usize> IoCapable<u64> for Mmio<SIZE> {}
> > +
> > +impl<const SIZE: usize> Io for Mmio<SIZE> {
> > +    const MIN_SIZE: usize = SIZE;
> > +
> > +    /// Returns the base address of this mapping.
> > +    #[inline]
> > +    fn addr(&self) -> usize {
> > +        self.0.addr()
> > +    }
> > +
> > +    /// Returns the maximum size of this mapping.
> > +    #[inline]
> > +    fn maxsize(&self) -> usize {
> > +        self.0.maxsize()
> > +    }
> > +
> > +    define_read!(fallible, try_read8, readb -> u8);
> > +    define_read!(fallible, try_read16, readw -> u16);
> > +    define_read!(fallible, try_read32, readl -> u32);
> >      define_read!(
> > +        fallible,
> >          #[cfg(CONFIG_64BIT)]
> > -        read64,
> >          try_read64,
> >          readq -> u64
> >      );
> >  
> > -    define_read!(read8_relaxed, try_read8_relaxed, readb_relaxed ->
> > u8);
> > -    define_read!(read16_relaxed, try_read16_relaxed, readw_relaxed ->
> > u16);
> > -    define_read!(read32_relaxed, try_read32_relaxed, readl_relaxed ->
> > u32);
> > +    define_write!(fallible, try_write8, writeb <- u8);
> > +    define_write!(fallible, try_write16, writew <- u16);
> > +    define_write!(fallible, try_write32, writel <- u32);
> > +    define_write!(
> > +        fallible,
> > +        #[cfg(CONFIG_64BIT)]
> > +        try_write64,
> > +        writeq <- u64
> > +    );
> > +}
> > +
> > +impl<const SIZE: usize> IoKnownSize for Mmio<SIZE> {
> > +    define_read!(infallible, read8, readb -> u8);
> > +    define_read!(infallible, read16, readw -> u16);
> > +    define_read!(infallible, read32, readl -> u32);
> >      define_read!(
> > +        infallible,
> >          #[cfg(CONFIG_64BIT)]
> > -        read64_relaxed,
> > -        try_read64_relaxed,
> > -        readq_relaxed -> u64
> > +        read64,
> > +        readq -> u64
> >      );
> >  
> > -    define_write!(write8, try_write8, writeb <- u8);
> > -    define_write!(write16, try_write16, writew <- u16);
> > -    define_write!(write32, try_write32, writel <- u32);
> > +    define_write!(infallible, write8, writeb <- u8);
> > +    define_write!(infallible, write16, writew <- u16);
> > +    define_write!(infallible, write32, writel <- u32);
> >      define_write!(
> > +        infallible,
> >          #[cfg(CONFIG_64BIT)]
> >          write64,
> > -        try_write64,
> >          writeq <- u64
> >      );
> > +}
> > +
> > +impl<const SIZE: usize> Mmio<SIZE> {
> > +    /// Converts an `MmioRaw` into an `Mmio` instance, providing the
> > accessors to the MMIO mapping.
> > +    ///
> > +    /// # Safety
> > +    ///
> > +    /// Callers must ensure that `addr` is the start of a valid I/O
> > mapped memory region of size
> > +    /// `maxsize`.
> > +    pub unsafe fn from_raw(raw: &MmioRaw<SIZE>) -> &Self {
> > +        // SAFETY: `Mmio` is a transparent wrapper around `MmioRaw`.
> > +        unsafe { &*core::ptr::from_ref(raw).cast() }
> > +    }
> > +
> > +    define_read!(infallible, pub read8_relaxed, readb_relaxed -> u8);
> > +    define_read!(infallible, pub read16_relaxed, readw_relaxed ->
> > u16);
> > +    define_read!(infallible, pub read32_relaxed, readl_relaxed ->
> > u32);
> > +    define_read!(
> > +        infallible,
> > +        #[cfg(CONFIG_64BIT)]
> > +        pub read64_relaxed,
> > +        readq_relaxed -> u64
> > +    );
> > +
> > +    define_read!(fallible, pub try_read8_relaxed, readb_relaxed ->
> > u8);
> > +    define_read!(fallible, pub try_read16_relaxed, readw_relaxed ->
> > u16);
> > +    define_read!(fallible, pub try_read32_relaxed, readl_relaxed ->
> > u32);
> > +    define_read!(
> > +        fallible,
> > +        #[cfg(CONFIG_64BIT)]
> > +        pub try_read64_relaxed,
> > +        readq_relaxed -> u64
> > +    );
> > +
> > +    define_write!(infallible, pub write8_relaxed, writeb_relaxed <-
> > u8);
> > +    define_write!(infallible, pub write16_relaxed, writew_relaxed <-
> > u16);
> > +    define_write!(infallible, pub write32_relaxed, writel_relaxed <-
> > u32);
> > +    define_write!(
> > +        infallible,
> > +        #[cfg(CONFIG_64BIT)]
> > +        pub write64_relaxed,
> > +        writeq_relaxed <- u64
> > +    );
> >  
> > -    define_write!(write8_relaxed, try_write8_relaxed, writeb_relaxed
> > <- u8);
> > -    define_write!(write16_relaxed, try_write16_relaxed,
> > writew_relaxed <- u16);
> > -    define_write!(write32_relaxed, try_write32_relaxed,
> > writel_relaxed <- u32);
> > +    define_write!(fallible, pub try_write8_relaxed, writeb_relaxed <-
> > u8);
> > +    define_write!(fallible, pub try_write16_relaxed, writew_relaxed
> > <- u16);
> > +    define_write!(fallible, pub try_write32_relaxed, writel_relaxed
> > <- u32); define_write!(
> > +        fallible,
> >          #[cfg(CONFIG_64BIT)]
> > -        write64_relaxed,
> > -        try_write64_relaxed,
> > +        pub try_write64_relaxed,
> >          writeq_relaxed <- u64
> >      );
> >  }
> > diff --git a/rust/kernel/io/mem.rs b/rust/kernel/io/mem.rs
> > index e4878c131c6d..620022cff401 100644
> > --- a/rust/kernel/io/mem.rs
> > +++ b/rust/kernel/io/mem.rs
> > @@ -16,8 +16,8 @@
> >              Region,
> >              Resource, //
> >          },
> > -        Io,
> > -        IoRaw, //
> > +        Mmio,
> > +        MmioRaw, //
> >      },
> >      prelude::*,
> >  };
> > @@ -212,7 +212,7 @@ pub fn new<'a>(io_request: IoRequest<'a>) -> impl
> > PinInit<Devres<Self>, Error> + }
> >  
> >  impl<const SIZE: usize> Deref for ExclusiveIoMem<SIZE> {
> > -    type Target = Io<SIZE>;
> > +    type Target = Mmio<SIZE>;
> >  
> >      fn deref(&self) -> &Self::Target {
> >          &self.iomem
> > @@ -226,10 +226,10 @@ fn deref(&self) -> &Self::Target {
> >  ///
> >  /// # Invariants
> >  ///
> > -/// [`IoMem`] always holds an [`IoRaw`] instance that holds a valid
> > pointer to the +/// [`IoMem`] always holds an [`MmioRaw`] instance
> > that holds a valid pointer to the /// start of the I/O memory mapped
> > region. pub struct IoMem<const SIZE: usize = 0> {
> > -    io: IoRaw<SIZE>,
> > +    io: MmioRaw<SIZE>,
> >  }
> >  
> >  impl<const SIZE: usize> IoMem<SIZE> {
> > @@ -264,7 +264,7 @@ fn ioremap(resource: &Resource) -> Result<Self> {
> >              return Err(ENOMEM);
> >          }
> >  
> > -        let io = IoRaw::new(addr as usize, size)?;
> > +        let io = MmioRaw::new(addr as usize, size)?;
> >          let io = IoMem { io };
> >  
> >          Ok(io)
> > @@ -287,10 +287,10 @@ fn drop(&mut self) {
> >  }
> >  
> >  impl<const SIZE: usize> Deref for IoMem<SIZE> {
> > -    type Target = Io<SIZE>;
> > +    type Target = Mmio<SIZE>;
> >  
> >      fn deref(&self) -> &Self::Target {
> >          // SAFETY: Safe as by the invariant of `IoMem`.
> > -        unsafe { Io::from_raw(&self.io) }
> > +        unsafe { Mmio::from_raw(&self.io) }
> >      }
> >  }
> > diff --git a/rust/kernel/io/poll.rs b/rust/kernel/io/poll.rs
> > index b1a2570364f4..75d1b3e8596c 100644
> > --- a/rust/kernel/io/poll.rs
> > +++ b/rust/kernel/io/poll.rs
> > @@ -45,12 +45,16 @@
> >  /// # Examples
> >  ///
> >  /// ```no_run
> > -/// use kernel::io::{Io, poll::read_poll_timeout};
> > +/// use kernel::io::{
> > +///     Io,
> > +///     Mmio,
> > +///     poll::read_poll_timeout, //
> > +/// };
> >  /// use kernel::time::Delta;
> >  ///
> >  /// const HW_READY: u16 = 0x01;
> >  ///
> > -/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
> > +/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) ->
> > Result { ///     read_poll_timeout(
> >  ///         // The `op` closure reads the value of a specific status
> > register. ///         || io.try_read16(0x1000),
> > @@ -128,12 +132,16 @@ pub fn read_poll_timeout<Op, Cond, T>(
> >  /// # Examples
> >  ///
> >  /// ```no_run
> > -/// use kernel::io::{poll::read_poll_timeout_atomic, Io};
> > +/// use kernel::io::{
> > +///     Io,
> > +///     Mmio,
> > +///     poll::read_poll_timeout_atomic, //
> > +/// };
> >  /// use kernel::time::Delta;
> >  ///
> >  /// const HW_READY: u16 = 0x01;
> >  ///
> > -/// fn wait_for_hardware<const SIZE: usize>(io: &Io<SIZE>) -> Result {
> > +/// fn wait_for_hardware<const SIZE: usize>(io: &Mmio<SIZE>) ->
> > Result { ///     read_poll_timeout_atomic(
> >  ///         // The `op` closure reads the value of a specific status
> > register. ///         || io.try_read16(0x1000),
> > diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
> > index 70e3854e7d8d..e3377397666e 100644
> > --- a/rust/kernel/pci/io.rs
> > +++ b/rust/kernel/pci/io.rs
> > @@ -8,8 +8,8 @@
> >      device,
> >      devres::Devres,
> >      io::{
> > -        Io,
> > -        IoRaw, //
> > +        Mmio,
> > +        MmioRaw, //
> >      },
> >      prelude::*,
> >      sync::aref::ARef, //
> > @@ -27,7 +27,7 @@
> >  /// memory mapped PCI BAR and its size.
> >  pub struct Bar<const SIZE: usize = 0> {
> >      pdev: ARef<Device>,
> > -    io: IoRaw<SIZE>,
> > +    io: MmioRaw<SIZE>,
> >      num: i32,
> >  }
> >  
> > @@ -63,7 +63,7 @@ pub(super) fn new(pdev: &Device, num: u32, name:
> > &CStr) -> Result<Self> { return Err(ENOMEM);
> >          }
> >  
> > -        let io = match IoRaw::new(ioptr, len as usize) {
> > +        let io = match MmioRaw::new(ioptr, len as usize) {
> >              Ok(io) => io,
> >              Err(err) => {
> >                  // SAFETY:
> > @@ -117,11 +117,11 @@ fn drop(&mut self) {
> >  }
> >  
> >  impl<const SIZE: usize> Deref for Bar<SIZE> {
> > -    type Target = Io<SIZE>;
> > +    type Target = Mmio<SIZE>;
> >  
> >      fn deref(&self) -> &Self::Target {
> >          // SAFETY: By the type invariant of `Self`, the MMIO range in
> > `self.io` is properly mapped.
> > -        unsafe { Io::from_raw(&self.io) }
> > +        unsafe { Mmio::from_raw(&self.io) }
> >      }
> >  }
> >  
> > diff --git a/samples/rust/rust_driver_pci.rs
> > b/samples/rust/rust_driver_pci.rs index ef04c6401e6a..bfb053059667
> > 100644 --- a/samples/rust/rust_driver_pci.rs
> > +++ b/samples/rust/rust_driver_pci.rs
> > @@ -7,6 +7,10 @@
> >  use kernel::{
> >      device::Core,
> >      devres::Devres,
> > +    io::{
> > +        Io,
> > +        IoKnownSize, //
> > +    },
> >      pci,
> >      prelude::*,
> >      sync::aref::ARef, //
> 

[PATCH v11 3/5] rust: io: factor out MMIO read/write macros

[Zhi Wang]

Refactor the existing MMIO accessors to use common call macros
instead of inlining the bindings calls in each `define_{read,write}!`
expansion.

This factoring separates the common offset/bounds checks from the
low-level call pattern, making it easier to add additional I/O accessor
families.

No functional change intended.

Cc: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 rust/kernel/io.rs | 147 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 102 insertions(+), 45 deletions(-)

diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index 152afdcbaf78..d62fd6714256 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -137,8 +137,65 @@ pub fn maxsize(&self) -> usize {
 #[repr(transparent)]
 pub struct Mmio<const SIZE: usize = 0>(MmioRaw<SIZE>);
 
+/// Internal helper macros used to invoke C MMIO read functions.
+///
+/// This macro is intended to be used by higher-level MMIO access macros (define_read) and provides
+/// a unified expansion for infallible vs. fallible read semantics. It emits a direct call into the
+/// corresponding C helper and performs the required cast to the Rust return type.
+///
+/// # Parameters
+///
+/// * `$c_fn` – The C function performing the MMIO read.
+/// * `$self` – The I/O backend object.
+/// * `$ty` – The type of the value to be read.
+/// * `$addr` – The MMIO address to read.
+///
+/// This macro does not perform any validation; all invariants must be upheld by the higher-level
+/// abstraction invoking it.
+macro_rules! call_mmio_read {
+    (infallible, $c_fn:ident, $self:ident, $type:ty, $addr:expr) => {
+        // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+        unsafe { bindings::$c_fn($addr as *const c_void) as $type }
+    };
+
+    (fallible, $c_fn:ident, $self:ident, $type:ty, $addr:expr) => {{
+        // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+        Ok(unsafe { bindings::$c_fn($addr as *const c_void) as $type })
+    }};
+}
+
+/// Internal helper macros used to invoke C MMIO write functions.
+///
+/// This macro is intended to be used by higher-level MMIO access macros (define_write) and provides
+/// a unified expansion for infallible vs. fallible write semantics. It emits a direct call into the
+/// corresponding C helper and performs the required cast to the Rust return type.
+///
+/// # Parameters
+///
+/// * `$c_fn` – The C function performing the MMIO write.
+/// * `$self` – The I/O backend object.
+/// * `$ty` – The type of the written value.
+/// * `$addr` – The MMIO address to write.
+/// * `$value` – The value to write.
+///
+/// This macro does not perform any validation; all invariants must be upheld by the higher-level
+/// abstraction invoking it.
+macro_rules! call_mmio_write {
+    (infallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr, $value:expr) => {
+        // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+        unsafe { bindings::$c_fn($value, $addr as *mut c_void) }
+    };
+
+    (fallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr, $value:expr) => {{
+        // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
+        unsafe { bindings::$c_fn($value, $addr as *mut c_void) };
+        Ok(())
+    }};
+}
+
 macro_rules! define_read {
-    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident -> $type_name:ty) => {
+    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $call_macro:ident($c_fn:ident) ->
+     $type_name:ty) => {
         /// Read IO data from a given offset known at compile time.
         ///
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
@@ -148,12 +205,13 @@ macro_rules! define_read {
         $vis fn $name(&self, offset: usize) -> $type_name {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
-            // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            unsafe { bindings::$c_fn(addr as *const c_void) }
+            // SAFETY: By the type invariant `addr` is a valid address for IO operations.
+            $call_macro!(infallible, $c_fn, self, $type_name, addr)
         }
     };
 
-    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $c_fn:ident -> $type_name:ty) => {
+    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $call_macro:ident($c_fn:ident) ->
+     $type_name:ty) => {
         /// Read IO data from a given offset.
         ///
         /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
@@ -162,15 +220,16 @@ macro_rules! define_read {
         $vis fn $try_name(&self, offset: usize) -> Result<$type_name> {
             let addr = self.io_addr::<$type_name>(offset)?;
 
-            // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            Ok(unsafe { bindings::$c_fn(addr as *const c_void) })
+            // SAFETY: By the type invariant `addr` is a valid address for IO operations.
+            $call_macro!(fallible, $c_fn, self, $type_name, addr)
         }
     };
 }
 pub(crate) use define_read;
 
 macro_rules! define_write {
-    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $c_fn:ident <- $type_name:ty) => {
+    (infallible, $(#[$attr:meta])* $vis:vis $name:ident, $call_macro:ident($c_fn:ident) <-
+     $type_name:ty) => {
         /// Write IO data from a given offset known at compile time.
         ///
         /// Bound checks are performed on compile time, hence if the offset is not known at compile
@@ -180,12 +239,12 @@ macro_rules! define_write {
         $vis fn $name(&self, value: $type_name, offset: usize) {
             let addr = self.io_addr_assert::<$type_name>(offset);
 
-            // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            unsafe { bindings::$c_fn(value, addr as *mut c_void) }
+            $call_macro!(infallible, $c_fn, self, $type_name, addr, value);
         }
     };
 
-    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $c_fn:ident <- $type_name:ty) => {
+    (fallible, $(#[$attr:meta])* $vis:vis $try_name:ident, $call_macro:ident($c_fn:ident) <-
+     $type_name:ty) => {
         /// Write IO data from a given offset.
         ///
         /// Bound checks are performed on runtime, it fails if the offset (plus the type size) is
@@ -194,9 +253,7 @@ macro_rules! define_write {
         $vis fn $try_name(&self, value: $type_name, offset: usize) -> Result {
             let addr = self.io_addr::<$type_name>(offset)?;
 
-            // SAFETY: By the type invariant `addr` is a valid address for MMIO operations.
-            unsafe { bindings::$c_fn(value, addr as *mut c_void) };
-            Ok(())
+            $call_macro!(fallible, $c_fn, self, $type_name, addr, value)
         }
     };
 }
@@ -468,46 +525,46 @@ fn maxsize(&self) -> usize {
         self.0.maxsize()
     }
 
-    define_read!(fallible, try_read8, readb -> u8);
-    define_read!(fallible, try_read16, readw -> u16);
-    define_read!(fallible, try_read32, readl -> u32);
+    define_read!(fallible, try_read8, call_mmio_read(readb) -> u8);
+    define_read!(fallible, try_read16, call_mmio_read(readw) -> u16);
+    define_read!(fallible, try_read32, call_mmio_read(readl) -> u32);
     define_read!(
         fallible,
         #[cfg(CONFIG_64BIT)]
         try_read64,
-        readq -> u64
+        call_mmio_read(readq) -> u64
     );
 
-    define_write!(fallible, try_write8, writeb <- u8);
-    define_write!(fallible, try_write16, writew <- u16);
-    define_write!(fallible, try_write32, writel <- u32);
+    define_write!(fallible, try_write8, call_mmio_write(writeb) <- u8);
+    define_write!(fallible, try_write16, call_mmio_write(writew) <- u16);
+    define_write!(fallible, try_write32, call_mmio_write(writel) <- u32);
     define_write!(
         fallible,
         #[cfg(CONFIG_64BIT)]
         try_write64,
-        writeq <- u64
+        call_mmio_write(writeq) <- u64
     );
 }
 
 impl<const SIZE: usize> IoKnownSize for Mmio<SIZE> {
-    define_read!(infallible, read8, readb -> u8);
-    define_read!(infallible, read16, readw -> u16);
-    define_read!(infallible, read32, readl -> u32);
+    define_read!(infallible, read8, call_mmio_read(readb) -> u8);
+    define_read!(infallible, read16, call_mmio_read(readw) -> u16);
+    define_read!(infallible, read32, call_mmio_read(readl) -> u32);
     define_read!(
         infallible,
         #[cfg(CONFIG_64BIT)]
         read64,
-        readq -> u64
+        call_mmio_read(readq) -> u64
     );
 
-    define_write!(infallible, write8, writeb <- u8);
-    define_write!(infallible, write16, writew <- u16);
-    define_write!(infallible, write32, writel <- u32);
+    define_write!(infallible, write8, call_mmio_write(writeb) <- u8);
+    define_write!(infallible, write16, call_mmio_write(writew) <- u16);
+    define_write!(infallible, write32, call_mmio_write(writel) <- u32);
     define_write!(
         infallible,
         #[cfg(CONFIG_64BIT)]
         write64,
-        writeq <- u64
+        call_mmio_write(writeq) <- u64
     );
 }
 
@@ -523,43 +580,43 @@ pub unsafe fn from_raw(raw: &MmioRaw<SIZE>) -> &Self {
         unsafe { &*core::ptr::from_ref(raw).cast() }
     }
 
-    define_read!(infallible, pub read8_relaxed, readb_relaxed -> u8);
-    define_read!(infallible, pub read16_relaxed, readw_relaxed -> u16);
-    define_read!(infallible, pub read32_relaxed, readl_relaxed -> u32);
+    define_read!(infallible, pub read8_relaxed, call_mmio_read(readb_relaxed) -> u8);
+    define_read!(infallible, pub read16_relaxed, call_mmio_read(readw_relaxed) -> u16);
+    define_read!(infallible, pub read32_relaxed, call_mmio_read(readl_relaxed) -> u32);
     define_read!(
         infallible,
         #[cfg(CONFIG_64BIT)]
         pub read64_relaxed,
-        readq_relaxed -> u64
+        call_mmio_read(readq_relaxed) -> u64
     );
 
-    define_read!(fallible, pub try_read8_relaxed, readb_relaxed -> u8);
-    define_read!(fallible, pub try_read16_relaxed, readw_relaxed -> u16);
-    define_read!(fallible, pub try_read32_relaxed, readl_relaxed -> u32);
+    define_read!(fallible, pub try_read8_relaxed, call_mmio_read(readb_relaxed) -> u8);
+    define_read!(fallible, pub try_read16_relaxed, call_mmio_read(readw_relaxed) -> u16);
+    define_read!(fallible, pub try_read32_relaxed, call_mmio_read(readl_relaxed) -> u32);
     define_read!(
         fallible,
         #[cfg(CONFIG_64BIT)]
         pub try_read64_relaxed,
-        readq_relaxed -> u64
+        call_mmio_read(readq_relaxed) -> u64
     );
 
-    define_write!(infallible, pub write8_relaxed, writeb_relaxed <- u8);
-    define_write!(infallible, pub write16_relaxed, writew_relaxed <- u16);
-    define_write!(infallible, pub write32_relaxed, writel_relaxed <- u32);
+    define_write!(infallible, pub write8_relaxed, call_mmio_write(writeb_relaxed) <- u8);
+    define_write!(infallible, pub write16_relaxed, call_mmio_write(writew_relaxed) <- u16);
+    define_write!(infallible, pub write32_relaxed, call_mmio_write(writel_relaxed) <- u32);
     define_write!(
         infallible,
         #[cfg(CONFIG_64BIT)]
         pub write64_relaxed,
-        writeq_relaxed <- u64
+        call_mmio_write(writeq_relaxed) <- u64
     );
 
-    define_write!(fallible, pub try_write8_relaxed, writeb_relaxed <- u8);
-    define_write!(fallible, pub try_write16_relaxed, writew_relaxed <- u16);
-    define_write!(fallible, pub try_write32_relaxed, writel_relaxed <- u32);
+    define_write!(fallible, pub try_write8_relaxed, call_mmio_write(writeb_relaxed) <- u8);
+    define_write!(fallible, pub try_write16_relaxed, call_mmio_write(writew_relaxed) <- u16);
+    define_write!(fallible, pub try_write32_relaxed, call_mmio_write(writel_relaxed) <- u32);
     define_write!(
         fallible,
         #[cfg(CONFIG_64BIT)]
         pub try_write64_relaxed,
-        writeq_relaxed <- u64
+        call_mmio_write(writeq_relaxed) <- u64
     );
 }
-- 
2.51.0

[PATCH v11 4/5] rust: pci: add config space read/write support

[Zhi Wang]

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 and
`IoCapable<T>` for u8, u16, and u32 to share offset validation and
bound-checking logic with other I/O backends.

Cc: Alexandre Courbot <acourbot@nvidia.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 rust/kernel/pci/io.rs | 161 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 161 insertions(+)

diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
index e3377397666e..e9c540fe80ac 100644
--- a/rust/kernel/pci/io.rs
+++ b/rust/kernel/pci/io.rs
@@ -8,6 +8,11 @@
     device,
     devres::Devres,
     io::{
+        define_read,
+        define_write,
+        Io,
+        IoCapable,
+        IoKnownSize,
         Mmio,
         MmioRaw, //
     },
@@ -16,6 +21,134 @@
 };
 use core::ops::Deref;
 
+/// 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.
+#[repr(usize)]
+pub(super) enum ConfigSpaceSize {
+    /// 256-byte legacy PCI configuration space.
+    Normal = 256,
+
+    /// 4096-byte PCIe extended configuration space.
+    Extended = 4096,
+}
+
+impl ConfigSpaceSize {
+    /// Get the raw value of this enum.
+    #[inline(always)]
+    pub(super) const fn as_raw(self) -> usize {
+        // CAST: PCI configuration space size is at most 4096 bytes, so the value always fits
+        // within `usize` without truncation or sign change.
+        self as usize
+    }
+}
+
+/// 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. `ConfigSpaceSize::Normal`
+/// or `ConfigSpaceSize::Extended`).
+pub struct ConfigSpace<'a, const SIZE: usize = { ConfigSpaceSize::Extended as usize }> {
+    pub(crate) pdev: &'a Device<device::Bound>,
+}
+
+/// Internal helper macros used to invoke C PCI configuration space read functions.
+///
+/// This macro is intended to be used by higher-level PCI configuration space access macros
+/// (define_read) and provides a unified expansion for infallible vs. fallible read semantics. It
+/// emits a direct call into the corresponding C helper and performs the required cast to the Rust
+/// return type.
+///
+/// # Parameters
+///
+/// * `$c_fn` – The C function performing the PCI configuration space write.
+/// * `$self` – The I/O backend object.
+/// * `$ty` – The type of the value to read.
+/// * `$addr` – The PCI configuration space offset to read.
+///
+/// This macro does not perform any validation; all invariants must be upheld by the higher-level
+/// abstraction invoking it.
+macro_rules! call_config_read {
+    (infallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr) => {{
+        let mut val: $ty = 0;
+        // SAFETY: By the type invariant `$self.pdev` is a valid address.
+        // CAST: The offset is cast to `i32` because the C functions expect a 32-bit signed offset
+        // parameter. PCI configuration space size is at most 4096 bytes, so the value always fits
+        // within `i32` without truncation or sign change.
+        // Return value from C function is ignored in infallible accessors.
+        let _ret = unsafe { bindings::$c_fn($self.pdev.as_raw(), $addr as i32, &mut val) };
+        val
+    }};
+}
+
+/// Internal helper macros used to invoke C PCI configuration space write functions.
+///
+/// This macro is intended to be used by higher-level PCI configuration space access macros
+/// (define_write) and provides a unified expansion for infallible vs. fallible read semantics. It
+/// emits a direct call into the corresponding C helper and performs the required cast to the Rust
+/// return type.
+///
+/// # Parameters
+///
+/// * `$c_fn` – The C function performing the PCI configuration space write.
+/// * `$self` – The I/O backend object.
+/// * `$ty` – The type of the written value.
+/// * `$addr` – The configuration space offset to write.
+/// * `$value` – The value to write.
+///
+/// This macro does not perform any validation; all invariants must be upheld by the higher-level
+/// abstraction invoking it.
+macro_rules! call_config_write {
+    (infallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr, $value:expr) => {
+        // SAFETY: By the type invariant `$self.pdev` is a valid address.
+        // CAST: The offset is cast to `i32` because the C functions expect a 32-bit signed offset
+        // parameter. PCI configuration space size is at most 4096 bytes, so the value always fits
+        // within `i32` without truncation or sign change.
+        // Return value from C function is ignored in infallible accessors.
+        let _ret = unsafe { bindings::$c_fn($self.pdev.as_raw(), $addr as i32, $value) };
+    };
+}
+
+// PCI configuration space supports 8, 16, and 32-bit accesses.
+impl<'a, const SIZE: usize> IoCapable<u8> for ConfigSpace<'a, SIZE> {}
+impl<'a, const SIZE: usize> IoCapable<u16> for ConfigSpace<'a, SIZE> {}
+impl<'a, const SIZE: usize> IoCapable<u32> for ConfigSpace<'a, SIZE> {}
+
+impl<'a, const SIZE: usize> Io for ConfigSpace<'a, SIZE> {
+    const MIN_SIZE: usize = SIZE;
+
+    /// Returns the base address of the I/O region. It is always 0 for configuration space.
+    #[inline]
+    fn addr(&self) -> usize {
+        0
+    }
+
+    /// Returns the maximum size of the configuration space.
+    #[inline]
+    fn maxsize(&self) -> usize {
+        self.pdev.cfg_size().map_or(0, |v| v as usize)
+    }
+
+    // PCI configuration space does not support fallible operations.
+    // The default implementations from the Io trait are not used.
+}
+
+/// Implement IoKnownSize for ConfigSpace with compile-time size.
+impl<'a, const SIZE: usize> IoKnownSize for ConfigSpace<'a, SIZE> {
+    define_read!(infallible, read8, call_config_read(pci_read_config_byte) -> u8);
+    define_read!(infallible, read16, call_config_read(pci_read_config_word) -> u16);
+    define_read!(infallible, read32, call_config_read(pci_read_config_dword) -> u32);
+
+    define_write!(infallible, write8, call_config_write(pci_write_config_byte) <- u8);
+    define_write!(infallible, write16, call_config_write(pci_write_config_word) <- u16);
+    define_write!(infallible, write32, call_config_write(pci_write_config_dword) <- u32);
+}
+
 /// A PCI BAR to perform I/O-Operations on.
 ///
 /// I/O backend assumes that the device is little-endian and will automatically
@@ -144,4 +277,32 @@ pub fn iomap_region<'a>(
     ) -> impl PinInit<Devres<Bar>, Error> + 'a {
         self.iomap_region_sized::<0>(bar, name)
     }
+
+    /// 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),
+            _ => {
+                debug_assert!(false);
+                Err(EINVAL)
+            }
+        }
+    }
+
+    /// Return an initialized config space object.
+    pub fn config_space<'a>(
+        &'a self,
+    ) -> Result<ConfigSpace<'a, { ConfigSpaceSize::Normal.as_raw() }>> {
+        Ok(ConfigSpace { pdev: self })
+    }
+
+    /// Return an initialized config space object.
+    pub fn config_space_extended<'a>(
+        &'a self,
+    ) -> Result<ConfigSpace<'a, { ConfigSpaceSize::Extended.as_raw() }>> {
+        Ok(ConfigSpace { pdev: self })
+    }
 }
-- 
2.51.0

Re: [PATCH v11 4/5] rust: pci: add config space read/write support

[Gary Guo]

On Wed Jan 21, 2026 at 2:23 PM GMT, 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 and
> `IoCapable<T>` for u8, u16, and u32 to share offset validation and
> bound-checking logic with other I/O backends.
>
> Cc: Alexandre Courbot <acourbot@nvidia.com>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Cc: Joel Fernandes <joelagnelf@nvidia.com>
> Signed-off-by: Zhi Wang <zhiw@nvidia.com>
> ---
>  rust/kernel/pci/io.rs | 161 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 161 insertions(+)
>
> diff --git a/rust/kernel/pci/io.rs b/rust/kernel/pci/io.rs
> index e3377397666e..e9c540fe80ac 100644
> --- a/rust/kernel/pci/io.rs
> +++ b/rust/kernel/pci/io.rs
> @@ -8,6 +8,11 @@
>      device,
>      devres::Devres,
>      io::{
> +        define_read,
> +        define_write,
> +        Io,
> +        IoCapable,
> +        IoKnownSize,
>          Mmio,
>          MmioRaw, //
>      },
> @@ -16,6 +21,134 @@
>  };
>  use core::ops::Deref;
>  
> +/// 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.
> +#[repr(usize)]
> +pub(super) enum ConfigSpaceSize {
> +    /// 256-byte legacy PCI configuration space.
> +    Normal = 256,
> +
> +    /// 4096-byte PCIe extended configuration space.
> +    Extended = 4096,
> +}
> +
> +impl ConfigSpaceSize {
> +    /// Get the raw value of this enum.
> +    #[inline(always)]
> +    pub(super) const fn as_raw(self) -> usize {
> +        // CAST: PCI configuration space size is at most 4096 bytes, so the value always fits
> +        // within `usize` without truncation or sign change.
> +        self as usize
> +    }
> +}
> +
> +/// 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. `ConfigSpaceSize::Normal`
> +/// or `ConfigSpaceSize::Extended`).
> +pub struct ConfigSpace<'a, const SIZE: usize = { ConfigSpaceSize::Extended as usize }> {

This is quite long to write. Given that it'll either be normal or extended, can
we just have two marker types instead? So you have

    ConfigSpace<Normal> and ConfigSpace<Extended>

Best,
Gary

> +    pub(crate) pdev: &'a Device<device::Bound>,
> +}
> +
> +/// Internal helper macros used to invoke C PCI configuration space read functions.
> +///
> +/// This macro is intended to be used by higher-level PCI configuration space access macros
> +/// (define_read) and provides a unified expansion for infallible vs. fallible read semantics. It
> +/// emits a direct call into the corresponding C helper and performs the required cast to the Rust
> +/// return type.
> +///
> +/// # Parameters
> +///
> +/// * `$c_fn` – The C function performing the PCI configuration space write.
> +/// * `$self` – The I/O backend object.
> +/// * `$ty` – The type of the value to read.
> +/// * `$addr` – The PCI configuration space offset to read.
> +///
> +/// This macro does not perform any validation; all invariants must be upheld by the higher-level
> +/// abstraction invoking it.
> +macro_rules! call_config_read {
> +    (infallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr) => {{
> +        let mut val: $ty = 0;
> +        // SAFETY: By the type invariant `$self.pdev` is a valid address.
> +        // CAST: The offset is cast to `i32` because the C functions expect a 32-bit signed offset
> +        // parameter. PCI configuration space size is at most 4096 bytes, so the value always fits
> +        // within `i32` without truncation or sign change.
> +        // Return value from C function is ignored in infallible accessors.
> +        let _ret = unsafe { bindings::$c_fn($self.pdev.as_raw(), $addr as i32, &mut val) };
> +        val
> +    }};
> +}
> +
> +/// Internal helper macros used to invoke C PCI configuration space write functions.
> +///
> +/// This macro is intended to be used by higher-level PCI configuration space access macros
> +/// (define_write) and provides a unified expansion for infallible vs. fallible read semantics. It
> +/// emits a direct call into the corresponding C helper and performs the required cast to the Rust
> +/// return type.
> +///
> +/// # Parameters
> +///
> +/// * `$c_fn` – The C function performing the PCI configuration space write.
> +/// * `$self` – The I/O backend object.
> +/// * `$ty` – The type of the written value.
> +/// * `$addr` – The configuration space offset to write.
> +/// * `$value` – The value to write.
> +///
> +/// This macro does not perform any validation; all invariants must be upheld by the higher-level
> +/// abstraction invoking it.
> +macro_rules! call_config_write {
> +    (infallible, $c_fn:ident, $self:ident, $ty:ty, $addr:expr, $value:expr) => {
> +        // SAFETY: By the type invariant `$self.pdev` is a valid address.
> +        // CAST: The offset is cast to `i32` because the C functions expect a 32-bit signed offset
> +        // parameter. PCI configuration space size is at most 4096 bytes, so the value always fits
> +        // within `i32` without truncation or sign change.
> +        // Return value from C function is ignored in infallible accessors.
> +        let _ret = unsafe { bindings::$c_fn($self.pdev.as_raw(), $addr as i32, $value) };
> +    };
> +}
> +
> +// PCI configuration space supports 8, 16, and 32-bit accesses.
> +impl<'a, const SIZE: usize> IoCapable<u8> for ConfigSpace<'a, SIZE> {}
> +impl<'a, const SIZE: usize> IoCapable<u16> for ConfigSpace<'a, SIZE> {}
> +impl<'a, const SIZE: usize> IoCapable<u32> for ConfigSpace<'a, SIZE> {}
> +
> +impl<'a, const SIZE: usize> Io for ConfigSpace<'a, SIZE> {
> +    const MIN_SIZE: usize = SIZE;
> +
> +    /// Returns the base address of the I/O region. It is always 0 for configuration space.
> +    #[inline]
> +    fn addr(&self) -> usize {
> +        0
> +    }
> +
> +    /// Returns the maximum size of the configuration space.
> +    #[inline]
> +    fn maxsize(&self) -> usize {
> +        self.pdev.cfg_size().map_or(0, |v| v as usize)
> +    }
> +
> +    // PCI configuration space does not support fallible operations.
> +    // The default implementations from the Io trait are not used.
> +}
> +
> +/// Implement IoKnownSize for ConfigSpace with compile-time size.
> +impl<'a, const SIZE: usize> IoKnownSize for ConfigSpace<'a, SIZE> {
> +    define_read!(infallible, read8, call_config_read(pci_read_config_byte) -> u8);
> +    define_read!(infallible, read16, call_config_read(pci_read_config_word) -> u16);
> +    define_read!(infallible, read32, call_config_read(pci_read_config_dword) -> u32);
> +
> +    define_write!(infallible, write8, call_config_write(pci_write_config_byte) <- u8);
> +    define_write!(infallible, write16, call_config_write(pci_write_config_word) <- u16);
> +    define_write!(infallible, write32, call_config_write(pci_write_config_dword) <- u32);
> +}
> +
>  /// A PCI BAR to perform I/O-Operations on.
>  ///
>  /// I/O backend assumes that the device is little-endian and will automatically
> @@ -144,4 +277,32 @@ pub fn iomap_region<'a>(
>      ) -> impl PinInit<Devres<Bar>, Error> + 'a {
>          self.iomap_region_sized::<0>(bar, name)
>      }
> +
> +    /// 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),
> +            _ => {
> +                debug_assert!(false);
> +                Err(EINVAL)
> +            }
> +        }
> +    }
> +
> +    /// Return an initialized config space object.
> +    pub fn config_space<'a>(
> +        &'a self,
> +    ) -> Result<ConfigSpace<'a, { ConfigSpaceSize::Normal.as_raw() }>> {
> +        Ok(ConfigSpace { pdev: self })
> +    }
> +
> +    /// Return an initialized config space object.
> +    pub fn config_space_extended<'a>(
> +        &'a self,
> +    ) -> Result<ConfigSpace<'a, { ConfigSpaceSize::Extended.as_raw() }>> {
> +        Ok(ConfigSpace { pdev: self })
> +    }
>  }

Re: [PATCH v11 4/5] rust: pci: add config space read/write support

[Danilo Krummrich]

On Wed Jan 21, 2026 at 4:36 PM CET, Gary Guo wrote:
>> +/// 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. `ConfigSpaceSize::Normal`
>> +/// or `ConfigSpaceSize::Extended`).
>> +pub struct ConfigSpace<'a, const SIZE: usize = { ConfigSpaceSize::Extended as usize }> {
>
> This is quite long to write. Given that it'll either be normal or extended, can
> we just have two marker types instead? So you have
>
>     ConfigSpace<Normal> and ConfigSpace<Extended>

I think in practice users don't have the need to write it anyways. You'd access
the config space with either

	let config = pdev.config_space()?;

or

	let config = pdev.config_space_extended()?;

i.e. there is no need to store an instance of the struct anywhere.

Should it turn out that we do need it for some reason in the future we can do
this as follow-up, I think.

Re: [PATCH v11 4/5] rust: pci: add config space read/write support

[Gary Guo]

On Wed Jan 21, 2026 at 5:12 PM GMT, Danilo Krummrich wrote:
> On Wed Jan 21, 2026 at 4:36 PM CET, Gary Guo wrote:
>>> +/// 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. `ConfigSpaceSize::Normal`
>>> +/// or `ConfigSpaceSize::Extended`).
>>> +pub struct ConfigSpace<'a, const SIZE: usize = { ConfigSpaceSize::Extended as usize }> {
>>
>> This is quite long to write. Given that it'll either be normal or extended, can
>> we just have two marker types instead? So you have
>>
>>     ConfigSpace<Normal> and ConfigSpace<Extended>
>
> I think in practice users don't have the need to write it anyways. You'd access
> the config space with either
>
> 	let config = pdev.config_space()?;
>
> or
>
> 	let config = pdev.config_space_extended()?;
>

I suspect when they need to write it, they'll just write `ConfigSpace<256>`
which'll be accepted by the compiler.

Also I don't see why we wouldn't want this to use types to begin with, even if
in practice users don't need to write out the type names.

Best,
Gary

> i.e. there is no need to store an instance of the struct anywhere.
>
> Should it turn out that we do need it for some reason in the future we can do
> this as follow-up, I think.

[PATCH v11 5/5] sample: rust: pci: add tests for config space routines

[Zhi Wang]

Add tests exercising the PCI configuration space helpers.

Suggested-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 samples/rust/rust_driver_pci.rs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
index bfb053059667..26f0887a74e8 100644
--- a/samples/rust/rust_driver_pci.rs
+++ b/samples/rust/rust_driver_pci.rs
@@ -5,6 +5,7 @@
 //! To make this driver probe, QEMU must be run with `-device pci-testdev`.
 
 use kernel::{
+    device::Bound,
     device::Core,
     devres::Devres,
     io::{
@@ -68,6 +69,32 @@ fn testdev(index: &TestIndex, bar: &Bar0) -> Result<u32> {
 
         Ok(bar.read32(Regs::COUNT))
     }
+
+    fn config_space(pdev: &pci::Device<Bound>) -> 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)
+        );
+
+        Ok(())
+    }
 }
 
 impl pci::Driver for SampleDriver {
@@ -99,6 +126,7 @@ fn probe(pdev: &pci::Device<Core>, info: &Self::IdInfo) -> impl PinInit<Self, Er
                         "pci-testdev data-match count: {}\n",
                         Self::testdev(info, bar)?
                     );
+                    Self::config_space(pdev)?;
                 },
                 pdev: pdev.into(),
             }))
-- 
2.51.0