Re: [PATCH v7 06/10] rust: io: use generic read/write accessors for primitive accesses

[Gary Guo]

On Tue Feb 24, 2026 at 2:21 PM GMT, Alexandre Courbot wrote:
> By providing the required `IoLoc` implementations on `usize`, we can
> leverage the generic accessors and reduce the number of unsafe blocks in
> the module.
>
> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>

To expand my comment on patch 5, if we have

    io.write(loc, value)

and
    
    io.try_write(loc, value)

then we would naturally have

    io.write::<u32>(loc, value)

becoming the generic equivalent of

    io.write32(loc, value)

for free.

Best,
Gary


> ---
>  rust/kernel/io.rs | 103 +++++++++++++++++++-----------------------------------
>  1 file changed, 35 insertions(+), 68 deletions(-)
>
> diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
> index fdd2549d8e13..256eba16ccc8 100644
> --- a/rust/kernel/io.rs
> +++ b/rust/kernel/io.rs
> @@ -275,6 +275,25 @@ fn try_init_default<F, E>(self, f: F) -> Result<IoWrite<T, Self>, E>
>      }
>  }
>  
> +/// Implements [`IoLoc<$ty>`] for [`usize`], allowing to use `usize` as a parameter of
> +/// [`Io::read`] and [`Io::write`].
> +macro_rules! impl_usize_ioloc {
> +    ($($ty:ty),*) => {
> +        $(
> +            impl IoLoc<$ty> for usize {
> +                type IoType = $ty;
> +
> +                fn offset(self) -> usize {
> +                    self
> +                }
> +            }
> +        )*
> +    }
> +}
> +
> +// Provide the ability to read any primitive type from a [`usize`].
> +impl_usize_ioloc!(u8, u16, u32, u64);
> +
>  /// A pending I/O write operation, bundling a value with the [`IoLoc`] it should be written to.
>  ///
>  /// Created by [`IoLoc::set`], [`IoLoc::zeroed`], [`IoLoc::default`], [`IoLoc::init`], or
> @@ -369,10 +388,7 @@ fn try_read8(&self, offset: usize) -> Result<u8>
>      where
>          Self: IoCapable<u8>,
>      {
> -        let address = self.io_addr::<u8>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        Ok(unsafe { self.io_read(address) })
> +        self.try_read(offset)
>      }
>  
>      /// Fallible 16-bit read with runtime bounds check.
> @@ -381,10 +397,7 @@ fn try_read16(&self, offset: usize) -> Result<u16>
>      where
>          Self: IoCapable<u16>,
>      {
> -        let address = self.io_addr::<u16>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        Ok(unsafe { self.io_read(address) })
> +        self.try_read(offset)
>      }
>  
>      /// Fallible 32-bit read with runtime bounds check.
> @@ -393,10 +406,7 @@ fn try_read32(&self, offset: usize) -> Result<u32>
>      where
>          Self: IoCapable<u32>,
>      {
> -        let address = self.io_addr::<u32>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        Ok(unsafe { self.io_read(address) })
> +        self.try_read(offset)
>      }
>  
>      /// Fallible 64-bit read with runtime bounds check.
> @@ -405,10 +415,7 @@ fn try_read64(&self, offset: usize) -> Result<u64>
>      where
>          Self: IoCapable<u64>,
>      {
> -        let address = self.io_addr::<u64>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        Ok(unsafe { self.io_read(address) })
> +        self.try_read(offset)
>      }
>  
>      /// Fallible 8-bit write with runtime bounds check.
> @@ -417,11 +424,7 @@ fn try_write8(&self, value: u8, offset: usize) -> Result
>      where
>          Self: IoCapable<u8>,
>      {
> -        let address = self.io_addr::<u8>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        unsafe { self.io_write(value, address) };
> -        Ok(())
> +        self.try_write(offset.set(value))
>      }
>  
>      /// Fallible 16-bit write with runtime bounds check.
> @@ -430,11 +433,7 @@ fn try_write16(&self, value: u16, offset: usize) -> Result
>      where
>          Self: IoCapable<u16>,
>      {
> -        let address = self.io_addr::<u16>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        unsafe { self.io_write(value, address) };
> -        Ok(())
> +        self.try_write(offset.set(value))
>      }
>  
>      /// Fallible 32-bit write with runtime bounds check.
> @@ -443,11 +442,7 @@ fn try_write32(&self, value: u32, offset: usize) -> Result
>      where
>          Self: IoCapable<u32>,
>      {
> -        let address = self.io_addr::<u32>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        unsafe { self.io_write(value, address) };
> -        Ok(())
> +        self.try_write(offset.set(value))
>      }
>  
>      /// Fallible 64-bit write with runtime bounds check.
> @@ -456,11 +451,7 @@ fn try_write64(&self, value: u64, offset: usize) -> Result
>      where
>          Self: IoCapable<u64>,
>      {
> -        let address = self.io_addr::<u64>(offset)?;
> -
> -        // SAFETY: `address` has been validated by `io_addr`.
> -        unsafe { self.io_write(value, address) };
> -        Ok(())
> +        self.try_write(offset.set(value))
>      }
>  
>      /// Infallible 8-bit read with compile-time bounds check.
> @@ -469,10 +460,7 @@ fn read8(&self, offset: usize) -> u8
>      where
>          Self: IoKnownSize + IoCapable<u8>,
>      {
> -        let address = self.io_addr_assert::<u8>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_read(address) }
> +        self.read(offset)
>      }
>  
>      /// Infallible 16-bit read with compile-time bounds check.
> @@ -481,10 +469,7 @@ fn read16(&self, offset: usize) -> u16
>      where
>          Self: IoKnownSize + IoCapable<u16>,
>      {
> -        let address = self.io_addr_assert::<u16>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_read(address) }
> +        self.read(offset)
>      }
>  
>      /// Infallible 32-bit read with compile-time bounds check.
> @@ -493,10 +478,7 @@ fn read32(&self, offset: usize) -> u32
>      where
>          Self: IoKnownSize + IoCapable<u32>,
>      {
> -        let address = self.io_addr_assert::<u32>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_read(address) }
> +        self.read(offset)
>      }
>  
>      /// Infallible 64-bit read with compile-time bounds check.
> @@ -505,10 +487,7 @@ fn read64(&self, offset: usize) -> u64
>      where
>          Self: IoKnownSize + IoCapable<u64>,
>      {
> -        let address = self.io_addr_assert::<u64>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_read(address) }
> +        self.read(offset)
>      }
>  
>      /// Infallible 8-bit write with compile-time bounds check.
> @@ -517,10 +496,7 @@ fn write8(&self, value: u8, offset: usize)
>      where
>          Self: IoKnownSize + IoCapable<u8>,
>      {
> -        let address = self.io_addr_assert::<u8>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_write(value, address) }
> +        self.write(offset.set(value))
>      }
>  
>      /// Infallible 16-bit write with compile-time bounds check.
> @@ -529,10 +505,7 @@ fn write16(&self, value: u16, offset: usize)
>      where
>          Self: IoKnownSize + IoCapable<u16>,
>      {
> -        let address = self.io_addr_assert::<u16>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_write(value, address) }
> +        self.write(offset.set(value))
>      }
>  
>      /// Infallible 32-bit write with compile-time bounds check.
> @@ -541,10 +514,7 @@ fn write32(&self, value: u32, offset: usize)
>      where
>          Self: IoKnownSize + IoCapable<u32>,
>      {
> -        let address = self.io_addr_assert::<u32>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_write(value, address) }
> +        self.write(offset.set(value))
>      }
>  
>      /// Infallible 64-bit write with compile-time bounds check.
> @@ -553,10 +523,7 @@ fn write64(&self, value: u64, offset: usize)
>      where
>          Self: IoKnownSize + IoCapable<u64>,
>      {
> -        let address = self.io_addr_assert::<u64>(offset);
> -
> -        // SAFETY: `address` has been validated by `io_addr_assert`.
> -        unsafe { self.io_write(value, address) }
> +        self.write(offset.set(value))
>      }
>  
>      /// Generic fallible read with runtime bounds check.