[PATCH v2 02/16] rust: io: add `IoRepr` trait

[Gary Guo <gary@garyguo.net>]

For types that are layout-compatible with an I/O capable type, we would
want the ability to use them directly for I/O operations. E.g.

    bitfield! {
        pub struct Foo(u32) {
            ...
        }
    }

    #[repr(C)]
    struct Bar {
        foo: Foo,
    }

    let mmio: Mmio<'_, Bar> = ...;
    io_read!(mmio, .foo)

Currently this feature is available from `register!()` macro but not
otherwise available with `io_read!`, `io_write!`. Support this by adding a
`IoRepr` type to denote the underlying I/O type to use for a specific type.

This makes the `IoLoc::IoType` and `Register::Storage` redundant; thus
remove them; also convert register methods to use the `read_val` and
`write_val` instead.

Signed-off-by: Gary Guo <gary@garyguo.net>
---
 rust/kernel/bitfield.rs    |   5 ++
 rust/kernel/io.rs          | 203 ++++++++++++++++++++++++++++++++-------------
 rust/kernel/io/register.rs |  59 +++++--------
 3 files changed, 170 insertions(+), 97 deletions(-)

diff --git a/rust/kernel/bitfield.rs b/rust/kernel/bitfield.rs
index 35ede53f2b8e..4bc92c62da06 100644
--- a/rust/kernel/bitfield.rs
+++ b/rust/kernel/bitfield.rs
@@ -308,6 +308,7 @@ macro_rules! bitfield {
         $(#[$attr])*
         #[repr(transparent)]
         #[derive(Clone, Copy, PartialEq, Eq)]
+        #[derive($crate::prelude::FromBytes, $crate::prelude::IntoBytes)]
         $vis struct $name {
             inner: $storage,
         }
@@ -346,6 +347,10 @@ fn from(val: $storage) -> $name {
                 Self::from_raw(val)
             }
         }
+
+        impl $crate::io::IoRepr for $name {
+            type Repr = $storage;
+        }
     };
 
     // Definitions requiring knowledge of individual fields: private and public field accessors,
diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs
index adfc555de7d0..71c6180ed745 100644
--- a/rust/kernel/io.rs
+++ b/rust/kernel/io.rs
@@ -276,6 +276,91 @@ pub trait IoCapable<T>: IoBackend {
     fn io_write<'a>(view: Self::View<'a, T>, value: T);
 }
 
+/// Safe transmute that performs size check on monomorphization-time.
+///
+/// Can be considered as generic version of [`zerocopy::transmute!`] macro but using the unstable
+/// `core::mem::transmute_neo` instead of [`core::mem::transmute`].
+#[inline(always)] // This is a no-op.
+fn transmute_neo<Src: IntoBytes, Dst: FromBytes>(val: Src) -> Dst {
+    const_assert!(size_of::<Src>() == size_of::<Dst>());
+
+    // SAFETY: `Src: IntoBytes` and `Dst: FromBytes` and we've checked size is the same.
+    unsafe { core::mem::transmute_copy(&core::mem::ManuallyDrop::new(val)) }
+}
+
+/// Trait indicating the underlying primitive types to be used for I/O operations.
+///
+/// Implementing trait allows arbitrary types to be used for I/O operations, not just raw
+/// primitives.
+///
+/// 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
+/// 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`].
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::io::*;
+/// #[repr(transparent)]
+/// #[derive(FromBytes, IntoBytes)]
+/// pub struct MyNewType(u32);
+///
+/// impl IoRepr for MyNewType {
+///     type Repr = u32;
+/// }
+///
+/// #[repr(C)]
+/// pub struct MyStruct {
+///     raw: u32,
+///     new_type: MyNewType,
+/// }
+///
+/// # fn test(mmio: Mmio<'_, MyStruct>) {
+/// // let mmio: Mmio<'_, MyStruct>;
+/// let val: u32 = io_read!(mmio, .raw); // Raw primitive read
+/// io_write!(mmio, .raw, val);          // Raw primitve write
+/// let val: MyNewType = io_read!(mmio, .new_type); // Read via `IoRepr`.
+/// io_write!(mmio, .new_type, val);                // Write via `IoRepr`.
+/// # }
+/// ```
+pub trait IoRepr: FromBytes + IntoBytes + Sized {
+    /// The backing I/O capable type.
+    type Repr: FromBytes + IntoBytes;
+
+    /// Convert from [`IoRepr::Repr`] to `Self`.
+    #[inline(always)]
+    fn from_repr(repr: Self::Repr) -> Self {
+        transmute_neo(repr)
+    }
+
+    /// Convert from `Self` to [`IoRepr::Repr`].
+    #[inline(always)]
+    fn into_repr(this: Self) -> Self::Repr {
+        transmute_neo(this)
+    }
+}
+
+macro_rules! impl_io_repr {
+    ($($ty:ty => $backing:ty,)*) => {
+        $(impl IoRepr for $ty {
+            type Repr = $backing;
+        })*
+    };
+}
+
+impl_io_repr! {
+    u8 => u8,
+    u16 => u16,
+    u32 => u32,
+    u64 => u64,
+    i8 => u8,
+    i16 => u16,
+    i32 => u32,
+    i64 => u64,
+}
+
 /// Trait indicating that an I/O backend supports memory copy operations.
 pub trait IoCopyable: IoBackend {
     /// Copy contents of `view` to `buffer`.
@@ -352,15 +437,12 @@ fn copy_write<T: IntoBytes>(view: Self::View<'_, T>, value: T) {
 ///
 /// - The valid `Base` to operate on. For most registers, this should be [`Region`].
 /// - The offset to access (returned by [`IoLoc::offset`]),
-/// - The width of the access (determined by [`IoLoc::IoType`]),
-/// - The type `T` in which the raw data is returned or provided.
+/// - The type `T` in which the data is returned or provided.
 ///
-/// `T` and `IoLoc::IoType` may differ: for instance, a typed register has `T` = the register type
-/// with its bitfields, and `IoType` = its backing primitive (e.g. `u32`).
+/// `T` is not necessarily the type for underlying I/O operation. Methods that take `IoLoc` have `T:
+/// IoRepr` bound and the `<T as IoRepr>::Repr` type would be used to perform I/O and converted to
+/// `T` instead.
 pub trait IoLoc<Base: ?Sized, T> {
-    /// Size ([`u8`], [`u16`], etc) of the I/O performed on the returned [`offset`](IoLoc::offset).
-    type IoType: Into<T> + From<T>;
-
     /// Consumes `self` and returns the offset of this location.
     fn offset(self) -> usize;
 }
@@ -371,8 +453,6 @@ macro_rules! impl_usize_ioloc {
     ($($ty:ty),*) => {
         $(
             impl<const SIZE: usize> IoLoc<Region<SIZE>, $ty> for usize {
-                type IoType = $ty;
-
                 #[inline(always)]
                 fn offset(self) -> usize {
                     self
@@ -536,10 +616,12 @@ fn try_cast<U>(self) -> Result<<Self::Backend as IoBackend>::View<'a, U>>
     #[inline]
     fn read_val(self) -> Self::Target
     where
-        Self::Backend: IoCapable<Self::Target>,
-        Self::Target: Sized,
+        Self::Target: IoRepr,
+        Self::Backend: IoCapable<<Self::Target as IoRepr>::Repr>,
     {
-        Self::Backend::io_read(self.as_view())
+        Self::Target::from_repr(Self::Backend::io_read(
+            self.as_view().cast::<<Self::Target as IoRepr>::Repr>(),
+        ))
     }
 
     /// Write a value to I/O.
@@ -558,10 +640,13 @@ fn read_val(self) -> Self::Target
     #[inline]
     fn write_val(self, value: Self::Target)
     where
-        Self::Backend: IoCapable<Self::Target>,
-        Self::Target: Sized,
+        Self::Target: IoRepr,
+        Self::Backend: IoCapable<<Self::Target as IoRepr>::Repr>,
     {
-        Self::Backend::io_write(self.as_view(), value)
+        Self::Backend::io_write(
+            self.as_view().cast::<<Self::Target as IoRepr>::Repr>(),
+            Self::Target::into_repr(value),
+        )
     }
 
     /// Copy-read from I/O memory.
@@ -683,7 +768,7 @@ fn copy_to_slice(self, data: &mut [u8])
     #[inline(always)]
     fn try_read8(self, offset: usize) -> Result<u8>
     where
-        usize: IoLoc<Self::Target, u8, IoType = u8>,
+        usize: IoLoc<Self::Target, u8>,
         Self::Backend: IoCapable<u8>,
     {
         self.try_read(offset)
@@ -693,7 +778,7 @@ fn try_read8(self, offset: usize) -> Result<u8>
     #[inline(always)]
     fn try_read16(self, offset: usize) -> Result<u16>
     where
-        usize: IoLoc<Self::Target, u16, IoType = u16>,
+        usize: IoLoc<Self::Target, u16>,
         Self::Backend: IoCapable<u16>,
     {
         self.try_read(offset)
@@ -703,7 +788,7 @@ fn try_read16(self, offset: usize) -> Result<u16>
     #[inline(always)]
     fn try_read32(self, offset: usize) -> Result<u32>
     where
-        usize: IoLoc<Self::Target, u32, IoType = u32>,
+        usize: IoLoc<Self::Target, u32>,
         Self::Backend: IoCapable<u32>,
     {
         self.try_read(offset)
@@ -713,7 +798,7 @@ fn try_read32(self, offset: usize) -> Result<u32>
     #[inline(always)]
     fn try_read64(self, offset: usize) -> Result<u64>
     where
-        usize: IoLoc<Self::Target, u64, IoType = u64>,
+        usize: IoLoc<Self::Target, u64>,
         Self::Backend: IoCapable<u64>,
     {
         self.try_read(offset)
@@ -723,7 +808,7 @@ fn try_read64(self, offset: usize) -> Result<u64>
     #[inline(always)]
     fn try_write8(self, value: u8, offset: usize) -> Result
     where
-        usize: IoLoc<Self::Target, u8, IoType = u8>,
+        usize: IoLoc<Self::Target, u8>,
         Self::Backend: IoCapable<u8>,
     {
         self.try_write(offset, value)
@@ -733,7 +818,7 @@ fn try_write8(self, value: u8, offset: usize) -> Result
     #[inline(always)]
     fn try_write16(self, value: u16, offset: usize) -> Result
     where
-        usize: IoLoc<Self::Target, u16, IoType = u16>,
+        usize: IoLoc<Self::Target, u16>,
         Self::Backend: IoCapable<u16>,
     {
         self.try_write(offset, value)
@@ -743,7 +828,7 @@ fn try_write16(self, value: u16, offset: usize) -> Result
     #[inline(always)]
     fn try_write32(self, value: u32, offset: usize) -> Result
     where
-        usize: IoLoc<Self::Target, u32, IoType = u32>,
+        usize: IoLoc<Self::Target, u32>,
         Self::Backend: IoCapable<u32>,
     {
         self.try_write(offset, value)
@@ -753,7 +838,7 @@ fn try_write32(self, value: u32, offset: usize) -> Result
     #[inline(always)]
     fn try_write64(self, value: u64, offset: usize) -> Result
     where
-        usize: IoLoc<Self::Target, u64, IoType = u64>,
+        usize: IoLoc<Self::Target, u64>,
         Self::Backend: IoCapable<u64>,
     {
         self.try_write(offset, value)
@@ -765,7 +850,7 @@ fn try_write64(self, value: u64, offset: usize) -> Result
     #[inline(always)]
     fn read8(self, offset: usize) -> u8
     where
-        usize: IoLoc<Self::Target, u8, IoType = u8>,
+        usize: IoLoc<Self::Target, u8>,
         Self::Backend: IoCapable<u8>,
     {
         self.read(offset)
@@ -777,7 +862,7 @@ fn read8(self, offset: usize) -> u8
     #[inline(always)]
     fn read16(self, offset: usize) -> u16
     where
-        usize: IoLoc<Self::Target, u16, IoType = u16>,
+        usize: IoLoc<Self::Target, u16>,
         Self::Backend: IoCapable<u16>,
     {
         self.read(offset)
@@ -789,7 +874,7 @@ fn read16(self, offset: usize) -> u16
     #[inline(always)]
     fn read32(self, offset: usize) -> u32
     where
-        usize: IoLoc<Self::Target, u32, IoType = u32>,
+        usize: IoLoc<Self::Target, u32>,
         Self::Backend: IoCapable<u32>,
     {
         self.read(offset)
@@ -801,7 +886,7 @@ fn read32(self, offset: usize) -> u32
     #[inline(always)]
     fn read64(self, offset: usize) -> u64
     where
-        usize: IoLoc<Self::Target, u64, IoType = u64>,
+        usize: IoLoc<Self::Target, u64>,
         Self::Backend: IoCapable<u64>,
     {
         self.read(offset)
@@ -813,7 +898,7 @@ fn read64(self, offset: usize) -> u64
     #[inline(always)]
     fn write8(self, value: u8, offset: usize)
     where
-        usize: IoLoc<Self::Target, u8, IoType = u8>,
+        usize: IoLoc<Self::Target, u8>,
         Self::Backend: IoCapable<u8>,
     {
         self.write(offset, value)
@@ -825,7 +910,7 @@ fn write8(self, value: u8, offset: usize)
     #[inline(always)]
     fn write16(self, value: u16, offset: usize)
     where
-        usize: IoLoc<Self::Target, u16, IoType = u16>,
+        usize: IoLoc<Self::Target, u16>,
         Self::Backend: IoCapable<u16>,
     {
         self.write(offset, value)
@@ -837,7 +922,7 @@ fn write16(self, value: u16, offset: usize)
     #[inline(always)]
     fn write32(self, value: u32, offset: usize)
     where
-        usize: IoLoc<Self::Target, u32, IoType = u32>,
+        usize: IoLoc<Self::Target, u32>,
         Self::Backend: IoCapable<u32>,
     {
         self.write(offset, value)
@@ -849,7 +934,7 @@ fn write32(self, value: u32, offset: usize)
     #[inline(always)]
     fn write64(self, value: u64, offset: usize)
     where
-        usize: IoLoc<Self::Target, u64, IoType = u64>,
+        usize: IoLoc<Self::Target, u64>,
         Self::Backend: IoCapable<u64>,
     {
         self.write(offset, value)
@@ -881,11 +966,12 @@ fn write64(self, value: u64, offset: usize)
     #[inline(always)]
     fn try_read<T, L>(self, location: L) -> Result<T>
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
     {
-        let view = io_view::<Self, L::IoType>(self, location.offset())?;
-        Ok(Self::Backend::io_read(view).into())
+        let view = io_view::<Self, T>(self, location.offset())?;
+        Ok(view.read_val())
     }
 
     /// Generic fallible write with runtime bounds check.
@@ -914,12 +1000,12 @@ fn try_read<T, L>(self, location: L) -> Result<T>
     #[inline(always)]
     fn try_write<T, L>(self, location: L, value: T) -> Result
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
     {
-        let view = io_view::<Self, L::IoType>(self, location.offset())?;
-        let io_value = value.into();
-        Self::Backend::io_write(view, io_value);
+        let view = io_view::<Self, T>(self, location.offset())?;
+        view.write_val(value);
         Ok(())
     }
 
@@ -958,9 +1044,10 @@ fn try_write<T, L>(self, location: L, value: T) -> Result
     #[inline(always)]
     fn try_write_reg<T, L, V>(self, value: V) -> Result
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
         V: LocatedRegister<Self::Target, Location = L, Value = T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
     {
         let (location, value) = value.into_io_op();
 
@@ -992,16 +1079,13 @@ fn try_write_reg<T, L, V>(self, value: V) -> Result
     #[inline(always)]
     fn try_update<T, L, F>(self, location: L, f: F) -> Result
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
         F: FnOnce(T) -> T,
     {
-        let view = io_view::<Self, L::IoType>(self, location.offset())?;
-
-        let value: T = Self::Backend::io_read(view).into();
-        let io_value = f(value).into();
-        Self::Backend::io_write(view, io_value);
-
+        let view = io_view::<Self, T>(self, location.offset())?;
+        view.write_val(f(view.read_val()));
         Ok(())
     }
 
@@ -1029,11 +1113,12 @@ fn try_update<T, L, F>(self, location: L, f: F) -> Result
     #[inline(always)]
     fn read<T, L>(self, location: L) -> T
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
     {
-        let view = io_view_assert::<Self, L::IoType>(self, location.offset());
-        Self::Backend::io_read(view).into()
+        let view = io_view_assert::<Self, T>(self, location.offset());
+        view.read_val()
     }
 
     /// Generic infallible write with compile-time bounds check.
@@ -1060,12 +1145,12 @@ fn read<T, L>(self, location: L) -> T
     #[inline(always)]
     fn write<T, L>(self, location: L, value: T)
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
     {
-        let view = io_view_assert::<Self, L::IoType>(self, location.offset());
-        let io_value = value.into();
-        Self::Backend::io_write(view, io_value);
+        let view = io_view_assert::<Self, T>(self, location.offset());
+        view.write_val(value)
     }
 
     /// Generic infallible write of a fully-located register value.
@@ -1102,9 +1187,10 @@ fn write<T, L>(self, location: L, value: T)
     #[inline(always)]
     fn write_reg<T, L, V>(self, value: V)
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
         V: LocatedRegister<Self::Target, Location = L, Value = T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
     {
         let (location, value) = value.into_io_op();
 
@@ -1136,14 +1222,13 @@ fn write_reg<T, L, V>(self, value: V)
     #[inline(always)]
     fn update<T, L, F>(self, location: L, f: F)
     where
+        T: IoRepr,
         L: IoLoc<Self::Target, T>,
-        Self::Backend: IoCapable<L::IoType>,
+        Self::Backend: IoCapable<<T as IoRepr>::Repr>,
         F: FnOnce(T) -> T,
     {
-        let view = io_view_assert::<Self, L::IoType>(self, location.offset());
-        let value: T = Self::Backend::io_read(view).into();
-        let io_value = f(value).into();
-        Self::Backend::io_write(view, io_value);
+        let view = io_view_assert::<Self, T>(self, location.offset());
+        view.write_val(f(view.read_val()));
     }
 }
 
diff --git a/rust/kernel/io/register.rs b/rust/kernel/io/register.rs
index 6cb07fc92cc3..d898b2b46d52 100644
--- a/rust/kernel/io/register.rs
+++ b/rust/kernel/io/register.rs
@@ -117,9 +117,6 @@
 
 /// Trait implemented by all registers.
 pub trait Register: Sized {
-    /// Backing primitive type of the register.
-    type Storage: Into<Self> + From<Self>;
-
     /// Start offset of the register.
     ///
     /// The interpretation of this offset depends on the type of the register.
@@ -135,8 +132,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for ()
 where
     T: FixedRegister,
 {
-    type IoType = T::Storage;
-
     #[inline(always)]
     fn offset(self) -> usize {
         T::OFFSET
@@ -149,8 +144,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for T
 where
     T: FixedRegister,
 {
-    type IoType = T::Storage;
-
     #[inline(always)]
     fn offset(self) -> usize {
         T::OFFSET
@@ -174,8 +167,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for FixedRegisterLoc<T>
 where
     T: FixedRegister,
 {
-    type IoType = T::Storage;
-
     #[inline(always)]
     fn offset(self) -> usize {
         T::OFFSET
@@ -246,8 +237,6 @@ impl<const SIZE: usize, T, B> IoLoc<Region<SIZE>, T> for RelativeRegisterLoc<T,
     T: RelativeRegister,
     B: RegisterBase<T::BaseFamily> + ?Sized,
 {
-    type IoType = T::Storage;
-
     #[inline(always)]
     fn offset(self) -> usize {
         RelativeRegisterLoc::offset(self)
@@ -289,8 +278,6 @@ impl<const SIZE: usize, T> IoLoc<Region<SIZE>, T> for RegisterArrayLoc<T>
 where
     T: RegisterArray,
 {
-    type IoType = T::Storage;
-
     #[inline(always)]
     fn offset(self) -> usize {
         T::OFFSET + self.0 * T::STRIDE
@@ -377,8 +364,6 @@ impl<const SIZE: usize, T, B> IoLoc<Region<SIZE>, T> for RelativeRegisterArrayLo
     T: RelativeRegisterArray,
     B: RegisterBase<T::BaseFamily> + ?Sized,
 {
-    type IoType = T::Storage;
-
     #[inline(always)]
     fn offset(self) -> usize {
         self.0.offset() + self.1 * T::STRIDE
@@ -831,8 +816,8 @@ macro_rules! register {
             { $($fields:tt)* }
     ) => {
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(@io_base $name($storage) @ $offset);
-        $crate::register!(@io_fixed $(#[$attr])* $vis $name($storage));
+        $crate::register!(@io_base $name @ $offset);
+        $crate::register!(@io_fixed $(#[$attr])* $vis $name);
     };
 
     // Creates an alias register of fixed offset register `alias` with its own fields.
@@ -842,10 +827,10 @@ macro_rules! register {
     ) => {
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
         $crate::register!(
-            @io_base $name($storage) @
+            @io_base $name @
             <$alias as $crate::io::register::Register>::OFFSET
         );
-        $crate::register!(@io_fixed $(#[$attr])* $vis $name($storage));
+        $crate::register!(@io_fixed $(#[$attr])* $vis $name);
     };
 
     // Creates a register at a relative offset from a base address provider.
@@ -854,8 +839,8 @@ macro_rules! register {
             { $($fields:tt)* }
     ) => {
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(@io_base $name($storage) @ $offset);
-        $crate::register!(@io_relative $vis $name($storage) @ $base);
+        $crate::register!(@io_base $name @ $offset);
+        $crate::register!(@io_relative $vis $name @ $base);
     };
 
     // Creates an alias register of relative offset register `alias` with its own fields.
@@ -865,9 +850,9 @@ macro_rules! register {
     ) => {
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
         $crate::register!(
-            @io_base $name($storage) @ <$alias as $crate::io::register::Register>::OFFSET
+            @io_base $name @ <$alias as $crate::io::register::Register>::OFFSET
         );
-        $crate::register!(@io_relative $vis $name($storage) @ $base);
+        $crate::register!(@io_relative $vis $name @ $base);
     };
 
     // Creates an array of registers at a fixed offset of the MMIO space.
@@ -878,8 +863,8 @@ macro_rules! register {
         $crate::build_assert::static_assert!(::core::mem::size_of::<$storage>() <= $stride);
 
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(@io_base $name($storage) @ $offset);
-        $crate::register!(@io_array $vis $name($storage) [ $size, stride = $stride ]);
+        $crate::register!(@io_base $name @ $offset);
+        $crate::register!(@io_array $vis $name [ $size, stride = $stride ]);
     };
 
     // Shortcut for contiguous array of registers (stride == size of element).
@@ -904,11 +889,11 @@ macro_rules! register {
 
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
         $crate::register!(
-            @io_base $name($storage) @
+            @io_base $name @
             <$alias as $crate::io::register::Register>::OFFSET
                 + $idx * <$alias as $crate::io::register::RegisterArray>::STRIDE
         );
-        $crate::register!(@io_fixed $(#[$attr])* $vis $name($storage));
+        $crate::register!(@io_fixed $(#[$attr])* $vis $name);
     };
 
     // Creates an array of registers at a relative offset from a base address provider.
@@ -920,9 +905,9 @@ macro_rules! register {
         $crate::build_assert::static_assert!(::core::mem::size_of::<$storage>() <= $stride);
 
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(@io_base $name($storage) @ $offset);
+        $crate::register!(@io_base $name @ $offset);
         $crate::register!(
-            @io_relative_array $vis $name($storage) [ $size, stride = $stride ] @ $base + $offset
+            @io_relative_array $vis $name [ $size, stride = $stride ] @ $base + $offset
         );
     };
 
@@ -949,11 +934,11 @@ macro_rules! register {
 
         $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
         $crate::register!(
-            @io_base $name($storage) @
+            @io_base $name @
                 <$alias as $crate::io::register::Register>::OFFSET +
                 $idx * <$alias as $crate::io::register::RegisterArray>::STRIDE
         );
-        $crate::register!(@io_relative $vis $name($storage) @ $base);
+        $crate::register!(@io_relative $vis $name @ $base);
     };
 
     // Generates the bitfield for the register.
@@ -970,16 +955,14 @@ macro_rules! register {
     };
 
     // Implementations shared by all registers types.
-    (@io_base $name:ident($storage:ty) @ $offset:expr) => {
+    (@io_base $name:ident @ $offset:expr) => {
         impl $crate::io::register::Register for $name {
-            type Storage = $storage;
-
             const OFFSET: usize = $offset;
         }
     };
 
     // Implementations of fixed registers.
-    (@io_fixed $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty)) => {
+    (@io_fixed $(#[$attr:meta])* $vis:vis $name:ident) => {
         impl $crate::io::register::FixedRegister for $name {}
 
         $(#[$attr])*
@@ -988,7 +971,7 @@ impl $crate::io::register::FixedRegister for $name {}
     };
 
     // Implementations of relative registers.
-    (@io_relative $vis:vis $name:ident ($storage:ty) @ $base:ident) => {
+    (@io_relative $vis:vis $name:ident @ $base:ident) => {
         impl $crate::io::register::WithBase for $name {
             type BaseFamily = $base;
         }
@@ -997,7 +980,7 @@ impl $crate::io::register::RelativeRegister for $name {}
     };
 
     // Implementations of register arrays.
-    (@io_array $vis:vis $name:ident ($storage:ty) [ $size:expr, stride = $stride:expr ]) => {
+    (@io_array $vis:vis $name:ident [ $size:expr, stride = $stride:expr ]) => {
         impl $crate::io::register::Array for $name {}
 
         impl $crate::io::register::RegisterArray for $name {
@@ -1008,7 +991,7 @@ impl $crate::io::register::RegisterArray for $name {
 
     // Implementations of relative array registers.
     (
-        @io_relative_array $vis:vis $name:ident ($storage:ty) [ $size:expr, stride = $stride:expr ]
+        @io_relative_array $vis:vis $name:ident [ $size:expr, stride = $stride:expr ]
             @ $base:ident + $offset:literal
     ) => {
         impl $crate::io::register::WithBase for $name {

-- 
2.54.0