linux.git/rust/kernel/io.rs, branch v7.1-rc2

rust: io: introduce `write_reg` and `LocatedRegister`

2026-03-17T19:04:11+00:00

Some I/O types, like fixed address registers, carry their location
alongside their values. For these types, the regular `Io::write` method
can lead into repeating the location information twice: once to provide
the location itself, another time to build the value.

We are also considering supporting making all register values carry
their full location information for convenience and safety.

Add a new `Io::write_reg` method that takes a single argument
implementing `LocatedRegister`, a trait that decomposes implementors
into a `(location, value)` tuple. This allows write operations on fixed
offset registers to be done while specifying their name only once.

Suggested-by: Danilo Krummrich 
Link: https://lore.kernel.org/all/DH0XBLXZD81K.22SWIZ1ZAOW1@kernel.org/
Signed-off-by: Alexandre Courbot 
Link: https://patch.msgid.link/20260314-register-v9-8-86805b2f7e9d@nvidia.com
[ Replace FIFO with VERSION register in the examples. - Danilo ]
Signed-off-by: Danilo Krummrich

rust: io: add `register!` macro

2026-03-17T19:04:11+00:00

Add a macro for defining hardware register types with I/O accessors.

Each register field is represented as a `Bounded` of the appropriate bit
width, ensuring field values are never silently truncated.

Fields can optionally be converted to/from custom types, either fallibly
or infallibly.

The address of registers can be direct, relative, or indexed, supporting
most of the patterns in which registers are arranged.

Suggested-by: Danilo Krummrich 
Link: https://lore.kernel.org/all/20250306222336.23482-6-dakr@kernel.org/
Co-developed-by: Gary Guo 
Signed-off-by: Gary Guo 
Signed-off-by: Alexandre Courbot 
Link: https://patch.msgid.link/20260314-register-v9-7-86805b2f7e9d@nvidia.com
[ * Improve wording and formatting of doc-comments,
  * Import build_assert!(),
  * Add missing inline annotations,
  * Call static_assert!() with absolute path,
  * Use expect instead of allow.

    - Danilo ]
Signed-off-by: Danilo Krummrich

rust: io: use generic read/write accessors for primitive accesses

2026-03-17T19:04:11+00:00

By providing the required `IoLoc` implementations on `usize`, we can
leverage the generic accessors and reduce the number of unsafe blocks in
the module.

This also allows us to directly call the generic `read/write/update`
methods with primitive types, so add examples illustrating this.

Signed-off-by: Alexandre Courbot 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260314-register-v9-6-86805b2f7e9d@nvidia.com
[ Slightly improve wording in doc-comment. - Danilo ]
Signed-off-by: Danilo Krummrich

rust: io: add IoLoc type and generic I/O accessors

2026-03-17T19:04:11+00:00

I/O accesses are defined by the following properties:

- An I/O location, which consists of a start address, a width, and a
  type to interpret the read value as,
- A value, which is returned for reads or provided for writes.

Introduce the `IoLoc` trait, which allows implementing types to fully
specify an I/O location.

This allows I/O operations to be made generic through the new `read` and
`write` methods.

This design will allow us to factorize the I/O code working with
primitives, and to introduce ways to perform I/O with a higher degree of
control through register types.

Co-developed-by: Gary Guo 
Signed-off-by: Gary Guo 
Signed-off-by: Alexandre Courbot 
Link: https://patch.msgid.link/20260314-register-v9-5-86805b2f7e9d@nvidia.com
[ Fix incorrect reference to io_addr_assert() in try_update(). - Danilo ]
Signed-off-by: Danilo Krummrich

rust: io: remove overloaded Io methods of Mmio

2026-03-17T19:02:10+00:00

Since `Mmio` now has the relevant implementations of `IoCapable`, the
default methods of `Io` can be used in place of the overloaded ones.
Remove them as well as the macros generating them.

Reviewed-by: Daniel Almeida 
Acked-by: Alice Ryhl 
Signed-off-by: Alexandre Courbot 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260206-io-v2-6-71dea20a06e6@nvidia.com
Signed-off-by: Danilo Krummrich

rust: pci: io: remove overloaded Io methods of ConfigSpace

2026-03-17T19:02:09+00:00

Since `ConfigSpace` now has the relevant implementations of `IoCapable`,
the default methods of `Io` can be used in place of the overloaded ones.
Remove them as well as the macros generating them.

Reviewed-by: Daniel Almeida 
Acked-by: Alice Ryhl 
Signed-off-by: Alexandre Courbot 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260206-io-v2-5-71dea20a06e6@nvidia.com
Signed-off-by: Danilo Krummrich

rust: io: remove legacy relaxed accessors of Mmio

2026-03-17T19:02:09+00:00

The relaxed access functionality is now provided by the `RelaxedMmio`
wrapper type, and we don't have any user of the legacy methods left.
Remove them.

Reviewed-by: Daniel Almeida 
Acked-by: Alice Ryhl 
Signed-off-by: Alexandre Courbot 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260206-io-v2-4-71dea20a06e6@nvidia.com
Signed-off-by: Danilo Krummrich

rust: io: provide Mmio relaxed ops through a wrapper type

2026-03-17T19:02:09+00:00

Relaxed I/O accessors for `Mmio` are currently implemented as an extra
set of methods that mirror the ones defined in `Io`, but with the
`_relaxed` suffix.

This makes these methods impossible to use with generic code, which is a
highly plausible proposition now that we have the `Io` trait.

Address this by adding a new `RelaxedMmio` wrapper type for `Mmio` that
provides its own `IoCapable` implementations relying on the relaxed C
accessors. This makes it possible to use relaxed operations on a `Mmio`
simply by wrapping it, and to use `RelaxedMmio` in code generic against
`Io`.

Acked-by: Alice Ryhl 
Signed-off-by: Alexandre Courbot 
Reviewed-by: Daniel Almeida 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260206-io-v2-3-71dea20a06e6@nvidia.com
[ Use kernel import style in examples. - Danilo ]
Signed-off-by: Danilo Krummrich

rust: io: turn IoCapable into a functional trait

2026-03-17T19:02:09+00:00

`IoCapable` 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.

Fix these issues by turning `IoCapable` into a functional trait that
includes the raw implementation of the I/O access for `T` using
unsafe methods that work with an arbitrary address.

This allows us to turn the default methods of `Io` into regular methods
that check the passed offset, turn it into an address, and call into the
corresponding `IoCapable` functions, removing the need to overload them
at all.

`IoCapable` must still be implemented for all supported primitive types,
which is still done more concisely using a macro, but this macro becomes
much simpler and does not require calling into another one.

Reviewed-by: Daniel Almeida 
Acked-by: Alice Ryhl 
Signed-off-by: Alexandre Courbot 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260206-io-v2-1-71dea20a06e6@nvidia.com
Signed-off-by: Danilo Krummrich

rust: io: macro_export io_define_read!() and io_define_write!()

2026-02-22T23:54:02+00:00

Currently, the define_read!() and define_write!() I/O macros are crate
public. The only user outside of the I/O module is PCI (for the
configurations space I/O backend). Consequently, when CONFIG_PCI=n this
causes a compile time warning [1].

In order to fix this, rename the macros to io_define_read!() and
io_define_write!() and use #[macro_export] to export them.

This is better than making the crate public visibility conditional, as
eventually subsystems will have their own crate.

Also, I/O backends are valid to be implemented by drivers as well. For
instance, there are devices (such as GPUs) that run firmware which
allows to program other devices only accessible through the primary
device through indirect I/O.

Since the macros are now public, also add the corresponding
documentation.

Fixes: 121d87b28e1d ("rust: io: separate generic I/O helpers from MMIO implementation")
Reported-by: Miguel Ojeda 
Closes: https://lore.kernel.org/driver-core/CANiq72khOYkt6t5zwMvSiyZvWWHMZuNCMERXu=7K=_5tT-8Pgg@mail.gmail.com/ [1]
Reviewed-by: Alice Ryhl 
Reviewed-by: Daniel Almeida 
Link: https://patch.msgid.link/20260216131534.65008-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich