linux-kernel - [PATCH v2 0/6] rust: io: turn IoCapable into a functional trait

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Message-Id: <20260206-io-v2-0-71dea20a06e6@nvidia.com>
Date: Fri, 06 Feb 2026 15:00:14 +0900
From: Alexandre Courbot <acourbot@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Daniel Almeida <daniel.almeida@...labora.com>, 
 Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, 
 Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
 Trevor Gross <tmgross@...ch.edu>, Bjorn Helgaas <bhelgaas@...gle.com>, 
 Krzysztof Wilczyński <kwilczynski@...nel.org>
Cc: driver-core@...ts.linux.dev, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, 
 Zhi Wang <zhiw@...dia.com>, Lyude Paul <lyude@...hat.com>, 
 Eliot Courtney <ecourtney@...dia.com>, 
 Alexandre Courbot <acourbot@...dia.com>
Subject: [PATCH v2 0/6] rust: io: turn IoCapable into a functional trait

`IoCapable<T>` is currently used as a marker trait to signal that the
methods of the `Io` trait corresponding to `T` have been overridden by
the implementor (the default implementations triggering a build-time
error).

This goes against the DRY principle and separates the signaling of the
capability from its implementation, making it possible to forget a step
while implementing a new `Io`.

Another undesirable side-effect is that it makes the implementation of
I/O backends boilerplate-y and convoluted: currently this is done using
two levels of imbricated macros that generate unsafe code.

This patchset fixes these issues by turning `IoCapable` into a
functional trait including the raw implementation of the I/O
accessors for `T` using unsafe methods that work with an arbitrary
address, and making the default methods of `Io` call into these
implementations after checking the bounds.

This makes overriding these accessors on all I/O backends unneeded,
resulting in a net -90 LoCs while avoiding a violation of the DRY
principle and reducing (and simplifying) the use of macros generating
unsafe code.

Patch 1 adds the `io_read` and `io_write` unsafe methods to `IoCapable`,
provides the required implementations for `Mmio` and `pci::ConfigSpace`,
and make the default I/O accessors of `Io` call into them instead of
failing.

Patches 2 to 4 get rid of the `_relaxed` variants we had in `Mmio`,
since these are not usable in code generic against `Io` and makes use of
the macros we want to remove. They are replaced by a `RelaxedMmio`
wrapper type that implements the required `IoCapable`s and is thus
usable in generic code.

Patches 5 and 6 remove the overloaded implementations of the `Io`
methods for `pci::ConfigSpace` and `Mmio`, respectively, while also
deleting the macros that have become unused.

There is more work coming on top of this patchset (notably the
`register!` macro with proper I/O), but I wanted to send this work first
as it stands on its own IMHO and is more digestible from a review
perspective.

The base for this patchset is `driver-core-testing`.

Cc: Zhi Wang <zhiw@...dia.com>
Cc: Lyude Paul <lyude@...hat.com>
Cc: Eliot Courtney <ecourtney@...dia.com>

Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
---
Changes in v2:
- Turn `RelaxedMmio` into an actual wrapper type and make it available
  through a `Mmio::relaxed()` method.
- Link to v1: https://patch.msgid.link/20260202-io-v1-0-9bb2177d23be@nvidia.com

---
Alexandre Courbot (6):
      rust: io: turn IoCapable into a functional trait
      rust: io: mem: use non-relaxed I/O ops in examples
      rust: io: provide Mmio relaxed ops through a wrapper type
      rust: io: remove legacy relaxed accessors of Mmio
      rust: pci: io: remove overloaded Io methods of ConfigSpace
      rust: io: remove overloaded Io methods of Mmio

 rust/kernel/io.rs     | 435 ++++++++++++++++++++++----------------------------
 rust/kernel/io/mem.rs |  10 +-
 rust/kernel/pci/io.rs |  99 ++++--------
 3 files changed, 227 insertions(+), 317 deletions(-)
---
base-commit: f55ae0bfa00e446ea751d09f468daeafc303e03f
change-id: 20260202-io-81fd368f7565

Best regards,
-- 
Alexandre Courbot <acourbot@...dia.com>