rust: io: separate generic I/O helpers from MMIO implementation

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 (try_read8, try_write8, etc.) and infallibile
  (read8, write8, etc.) I/O methods with runtime bounds checking and
  compile-time bounds checking.

- IoKnownSize trait: The marker trait for types support infallible I/O
  methods.

Move the MMIO-specific logic into a dedicated Mmio<SIZE> type that
implements the Io 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>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260121202212.4438-3-zhiw@nvidia.com
[ Add #[expect(unused)] to define_{read,write}!(). - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

1 files changed, 6 insertions, 6 deletions

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 @@ use crate::{
     device,
     devres::Devres,
     io::{
-        Io,
-        IoRaw, //
+        Mmio,
+        MmioRaw, //
     },
     prelude::*,
     sync::aref::ARef, //
@@ -27,7 +27,7 @@ use core::ops::Deref;
 /// 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 @@ impl<const SIZE: usize> Bar<SIZE> {
             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 @@ impl<const SIZE: usize> Drop for Bar<SIZE> {
 }
 
 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) }
     }
 }