linux.git/rust/kernel/io.rs, branch v7.2-rc7

rust: io: gate ioremap doctests on CONFIG_HAS_IOMEM

2026-08-06T14:05:50+00:00

The doc examples in io.rs and devres.rs directly call
bindings::ioremap() and bindings::iounmap(), which do not exist when
CONFIG_HAS_IOMEM is not set. This causes build failures with
CONFIG_RUST_KERNEL_DOCTESTS=y on such configurations (e.g. s390
allnoconfig).

Gate the affected doctests with `#![cfg(CONFIG_HAS_IOMEM)]` so they are
skipped when IOMEM is unavailable.

Fixes: 3f70ebe63858 ("s390: Enable Rust support")
Reviewed-by: Arnd Bergmann 
Link: https://patch.msgid.link/20260805212920.1996937-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich

rust: io: gate ioremap/iounmap on CONFIG_HAS_IOMEM

2026-08-06T14:05:50+00:00

s390 does not provide ioremap()/iounmap() when CONFIG_HAS_IOMEM is not
set (which requires CONFIG_PCI on that architecture). This causes a
build failure with Rust enabled on e.g. s390 allnoconfig:

	In file included from rust/helpers/helpers.c:68:
	rust/helpers/io.c:8:9: error: call to undeclared function 'ioremap'; ISO C99 and later do not support implicit function declarations
	      [-Wimplicit-function-declaration]
	    8 |         return ioremap(offset, size);
	      |                ^
	rust/helpers/io.c:19:2: error: call to undeclared function 'iounmap'; ISO C99 and later do not support implicit function declarations
	      [-Wimplicit-function-declaration]
	   19 |         iounmap(addr);

Guard the C helpers behind #ifdef CONFIG_HAS_IOMEM and cfg-gate the Rust
io::mem module, such that IoMem, ExclusiveIoMem and IoRequest are not
available without CONFIG_HAS_IOMEM.

Note that the C API is inconsistent about this. For instance,
devm_ioremap() has no stub and produces a link failure without
CONFIG_HAS_IOMEM, whereas devm_platform_ioremap_resource() provides an
inline stub returning -EINVAL.

The approach taken here (compile-time gating) matches the former, which
is slightly more appropriate since any driver performing MMIO currently
requires CONFIG_HAS_IOMEM.

Ideally, s390 should provide ioremap()/iounmap() stubs unconditionally
(as UML already does), removing the need for any config gating as
discussed in [1]; a follow-up patch for s390 is expected.

Cc: Arnd Bergmann 
Reported-by: Miguel Ojeda 
Closes: https://lore.kernel.org/all/20260803180931.97202-1-ojeda@kernel.org [1]
Fixes: 3f70ebe63858 ("s390: Enable Rust support")
Reviewed-by: Arnd Bergmann 
Link: https://patch.msgid.link/20260805212920.1996937-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich

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