[PATCH v8 3/5] rust: io: factor out MMIO read/write macros

Zhi Wang
2026-01-13T09:23:55Z

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 | 149 ++++++++++++++++++++++++++++++++--------------
1 file changed, 104 insertions(+), 45 deletions(-)

diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index 6e7f0d48ba3e..65a68da168c0 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
+///
+/// * `$c_fn` – The C function performing the MMIO write.
+/// * `$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 $type })
+ }};
+}
+
+/// Internal helper macros used to invoke C MMIO write functions.
+///
+/// This macro is intended to be used by higher-level MMIO access macros (define_write) and provides
+/// a unified expansion for infallible vs. fallible read semantics. It emits a direct call into the
+/// corresponding C helper and performs the required cast to the Rust return type.
+///
+/// # Parameters
+///
+/// * `$c_fn` – The C function performing the MMIO 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
@@ -162,14 +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
@@ -179,12 +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
@@ -193,12 +253,11 @@ 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)
}
};
}
+pub(crate) use define_write;

/// Checks whether an access of type `U` at the given `offset`
/// is valid within this region.
@@ -332,37 +391,37 @@ fn maxsize(&self) -> usize {
}

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_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);
}

impl<const SIZE: usize> Io for Mmio<SIZE> {
- 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_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);
}

#[cfg(CONFIG_64BIT)]
impl<const SIZE: usize> IoKnownSize64 for Mmio<SIZE> {
- define_read!(infallible, read64, readq -> u64);
+ define_read!(infallible, read64, call_mmio_read(readq) -> u64);

- define_write!(infallible, write64, writeq <- u64);
+ define_write!(infallible, write64, call_mmio_write(writeq) <- u64);
}

#[cfg(CONFIG_64BIT)]
impl<const SIZE: usize> Io64 for Mmio<SIZE> {
- define_read!(fallible, try_read64, readq -> u64);
+ define_read!(fallible, try_read64, call_mmio_read(readq) -> u64);

- define_write!(fallible, try_write64, writeq <- u64);
+ define_write!(fallible, try_write64, call_mmio_write(writeq) <- u64);
}

impl<const SIZE: usize> Mmio<SIZE> {
@@ -377,43 +436,43 @@ 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