Re: [PATCH v2 03/16] rust: io: support register projections

On Thu Aug 6, 2026 at 1:35 AM JST, Gary Guo wrote:
> `IoLoc`s themselves just describe a projection from a region to a concrete
> register. Thus, support it in `io_project` macro too. Also, update methods
> that operate on `IoLoc` to use I/O projection.
>
> Documentation of `io_project!` is not expanded yet as the example works
> better when `register!` type can specify base type. `io_read!` and
> `io_write!` gains the ability to operate on registers as corollary of the
> capability of `io_project!`. Examples are not added because `read` and
> `write` is still preferrably used instead.
>
> Signed-off-by: Gary Guo <[email protected]>
> ---
>  rust/kernel/io.rs | 58 ++++++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 47 insertions(+), 11 deletions(-)
>
> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> index 71c6180ed745..ae18890866b6 100644
> --- a/rust/kernel/io.rs
> +++ b/rust/kernel/io.rs
> @@ -295,7 +295,7 @@ fn transmute_neo<Src: IntoBytes, Dst: FromBytes>(val: Src) -> Dst {
>  ///
>  /// The layout of the type and the underlying primitive must match; this is enforced via const
>  /// assertions when I/O methods are used, as the type system cannot represent this.
> -/// [`IoRepr::from_repr`] and [`IoRepr::into_expr`] can be overridden for conversions, however it
> +/// [`IoRepr::from_repr`] and [`IoRepr::into_repr`] can be overridden for conversions, however it

This typo was introduced in patch 2, let's fix it there.

>  /// should be noted that they are only invoked on value read/write operations and are not invoked
>  /// on byte operations such as [`Io::copy_read`].
>  ///
> @@ -970,8 +970,7 @@ fn try_read<T, L>(self, location: L) -> Result<T>
>          L: IoLoc<Self::Target, T>,
>          Self::Backend: IoCapable<<T as IoRepr>::Repr>,
>      {
> -        let view = io_view::<Self, T>(self, location.offset())?;
> -        Ok(view.read_val())
> +        Ok(io_read!(self, try: location))
>      }
>  
>      /// Generic fallible write with runtime bounds check.
> @@ -1004,8 +1003,7 @@ fn try_write<T, L>(self, location: L, value: T) -> Result
>          L: IoLoc<Self::Target, T>,
>          Self::Backend: IoCapable<<T as IoRepr>::Repr>,
>      {
> -        let view = io_view::<Self, T>(self, location.offset())?;
> -        view.write_val(value);
> +        io_write!(self, try: location, value);
>          Ok(())
>      }
>  
> @@ -1084,7 +1082,7 @@ fn try_update<T, L, F>(self, location: L, f: F) -> Result
>          Self::Backend: IoCapable<<T as IoRepr>::Repr>,
>          F: FnOnce(T) -> T,
>      {
> -        let view = io_view::<Self, T>(self, location.offset())?;
> +        let view = io_project!(self, try: location);
>          view.write_val(f(view.read_val()));
>          Ok(())
>      }
> @@ -1117,8 +1115,7 @@ fn read<T, L>(self, location: L) -> T
>          L: IoLoc<Self::Target, T>,
>          Self::Backend: IoCapable<<T as IoRepr>::Repr>,
>      {
> -        let view = io_view_assert::<Self, T>(self, location.offset());
> -        view.read_val()
> +        io_read!(self, build: location)
>      }
>  
>      /// Generic infallible write with compile-time bounds check.
> @@ -1149,8 +1146,7 @@ fn write<T, L>(self, location: L, value: T)
>          L: IoLoc<Self::Target, T>,
>          Self::Backend: IoCapable<<T as IoRepr>::Repr>,
>      {
> -        let view = io_view_assert::<Self, T>(self, location.offset());
> -        view.write_val(value)
> +        io_write!(self, build: location, value);
>      }
>  
>      /// Generic infallible write of a fully-located register value.
> @@ -1227,7 +1223,7 @@ fn update<T, L, F>(self, location: L, f: F)
>          Self::Backend: IoCapable<<T as IoRepr>::Repr>,
>          F: FnOnce(T) -> T,
>      {
> -        let view = io_view_assert::<Self, T>(self, location.offset());
> +        let view = io_project!(self, build: location);
>          view.write_val(f(view.read_val()));
>      }
>  }
> @@ -1772,6 +1768,25 @@ pub unsafe fn project_view<U: ?Sized + KnownSize>(
>          // SAFETY: Per safety requirement.
>          unsafe { T::Backend::project_view::<T::Target, _>(self.0, ptr) }
>      }
> +
> +    #[inline(always)]
> +    pub fn try_project_loc<U, L>(

nit: missing documentation

> +        self,
> +        location: L,
> +    ) -> Result<<T::Backend as IoBackend>::View<'a, U>>
> +    where
> +        L: IoLoc<T::Target, U>,
> +    {
> +        io_view::<_, U>(self.0, location.offset())
> +    }
> +
> +    #[inline(always)]
> +    pub fn project_loc<U, L>(self, location: L) -> <T::Backend as IoBackend>::View<'a, U>

ditto.