rust: io: register: reimplement as proc macro

The existing `register!` macro is implemented as a declarative macro.
Reimplement it as proc macro instead, with no functional changes intended.

The old implementation produces unhelpful diagnostics when things go wrong.
For example, for code like

    register! {
        pub(crate) TESTREG(u32) {
            31:0    data;
        }
    }

which misses out the "@ offset" part of the specification, and the
following error is produced:

error: no rules expected `{`
   --> test.rs:42:5
    |
 42 | /     register! {
 43 | |         pub(crate) TESTREG(u32) {
 44 | |             31:0    data;
...   |
100 | |     }
    | |_____^ no rules expected this token in macro call

which isn't very helpful. With the proc macro implementation, the following
error is produced:

error: expected `@` or `=>`
  --> tests.rs:43:33
   |
43 |         pub(crate) TESTREG(u32) {
   |                                 ^

which is much more helpful. Apart from diagnostics, proc macro also has a
benefit of not having follow-set restrictions, which makes syntax like

    register!(name: ty @ offset);

possible; declarative macro will reject this as `@` is not in the
follow-set of "ty" metavariable kind.

Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260901-typed_register-v4-1-5552b1d59525@garyguo.net
[ Fix typo in module-level doc comment and fix ArrayDef syntax
  description to match the actual macro syntax. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

1 files changed, 2 insertions, 222 deletions

diff --git a/rust/kernel/io/register.rs b/rust/kernel/io/register.rs
index 03dfd2ff48c7..6a19552ffb95 100644
--- a/rust/kernel/io/register.rs
+++ b/rust/kernel/io/register.rs
@@ -801,227 +801,7 @@ where
 /// ```
 #[macro_export]
 macro_rules! register {
-    // Entry point for the macro, allowing multiple registers to be defined in one call.
-    // It matches all possible register declaration patterns to dispatch them to corresponding
-    // `@reg` rule that defines a single register.
-    //
-    // TODO: change `alias:ident` to `alias:path` once relative registers are replaced by I/O
-    // projections.
-    (
-        $(
-            $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty)
-                $([ $size:expr $(, stride = $stride:expr)? ])?
-                $(@ $($base:ident +)? $offset:literal)?
-                $(=> $alias:ident $(+ $alias_offset:ident)? $([$alias_idx:expr])? )?
-            { $($fields:tt)* }
-        )*
-    ) => {
-        $(
-        $crate::register!(
-            @reg $(#[$attr])* $vis $name ($storage) $([$size $(, stride = $stride)?])?
-                $(@ $($base +)? $offset)?
-                $(=> $alias $(+ $alias_offset)? $([$alias_idx])? )?
-            { $($fields)* }
-        );
-        )*
-    };
-
-    // All the rules below are private helpers.
-
-    // Creates a register at a fixed offset of the MMIO space.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty) @ $offset:literal
-            { $($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);
-    };
-
-    // Creates an alias register of fixed offset register `alias` with its own fields.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty) => $alias:path
-            { $($fields:tt)* }
-    ) => {
-        $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(
-            @io_base $name($storage) @
-            <$alias as $crate::io::register::Register>::OFFSET
-        );
-        $crate::register!(@io_fixed $(#[$attr])* $vis $name);
-    };
-
-    // Creates a register at a relative offset from a base address provider.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty) @ $base:ident + $offset:literal
-            { $($fields:tt)* }
-    ) => {
-        $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(@io_base $name($storage) @ $offset);
-        $crate::register!(@io_relative $name @ $base);
-    };
-
-    // Creates an alias register of relative offset register `alias` with its own fields.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty) => $base:ident + $alias:ident
-            { $($fields:tt)* }
-    ) => {
-        $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(
-            @io_base $name($storage) @ <$alias as $crate::io::register::Register>::OFFSET
-        );
-        $crate::register!(@io_relative $name @ $base);
-    };
-
-    // Creates an array of registers at a fixed offset of the MMIO space.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty)
-            [ $size:expr, stride = $stride:expr ] @ $offset:literal { $($fields:tt)* }
-    ) => {
-        $crate::build_assert::static_assert!(::core::mem::size_of::<$storage>() <= $stride);
-
-        $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(@io_base $name($storage) @ $offset);
-        $crate::register!(@io_array $name [ $size, stride = $stride ]);
-    };
-
-    // Shortcut for contiguous array of registers (stride == size of element).
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty) [ $size:expr ] @ $offset:literal
-            { $($fields:tt)* }
-    ) => {
-        $crate::register!(
-            @reg $(#[$attr])* $vis $name($storage)
-                [ $size, stride = ::core::mem::size_of::<$storage>() ]
-                @ $offset { $($fields)* }
-        );
-    };
-
-    // Creates an alias of register `idx` of array of registers `alias` with its own fields.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty) => $alias:path [ $idx:expr ]
-            { $($fields:tt)* }
-    ) => {
-        $crate::build_assert::static_assert!(
-            $idx < <$alias as $crate::io::register::RegisterArray>::SIZE
-        );
-
-        $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(
-            @io_base $name($storage) @
-            <$alias as $crate::io::register::Register>::OFFSET
-                + $idx * <$alias as $crate::io::register::RegisterArray>::STRIDE
-        );
-        $crate::register!(@io_fixed $(#[$attr])* $vis $name);
-    };
-
-    // Creates an array of registers at a relative offset from a base address provider.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty)
-            [ $size:expr, stride = $stride:expr ]
-            @ $base:ident + $offset:literal { $($fields:tt)* }
-    ) => {
-        $crate::build_assert::static_assert!(::core::mem::size_of::<$storage>() <= $stride);
-
-        $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(@io_base $name($storage) @ $offset);
-        $crate::register!(@io_relative_array $name [ $size, stride = $stride ] @ $base);
-    };
-
-    // Shortcut for contiguous array of relative registers (stride == size of element).
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty) [ $size:expr ]
-            @ $base:ident + $offset:literal { $($fields:tt)* }
-    ) => {
-        $crate::register!(
-            @reg $(#[$attr])* $vis $name($storage)
-                [ $size, stride = ::core::mem::size_of::<$storage>() ]
-                @ $base + $offset { $($fields)* }
-        );
-    };
-
-    // Creates an alias of register `idx` of relative array of registers `alias` with its own
-    // fields.
-    (
-        @reg $(#[$attr:meta])* $vis:vis $name:ident ($storage:ty)
-            => $base:ident + $alias:ident [ $idx:expr ] { $($fields:tt)* }
-    ) => {
-        $crate::build_assert::static_assert!(
-            $idx < <$alias as $crate::io::register::RegisterArray>::SIZE
-        );
-
-        $crate::register!(@bitfield $(#[$attr])* $vis struct $name($storage) { $($fields)* });
-        $crate::register!(
-            @io_base $name($storage) @
-                <$alias as $crate::io::register::Register>::OFFSET +
-                $idx * <$alias as $crate::io::register::RegisterArray>::STRIDE
-        );
-        $crate::register!(@io_relative $name @ $base);
-    };
-
-    // Generates the bitfield for the register.
-    //
-    // `#[allow(non_camel_case_types)]` is added since register names typically use
-    // `SCREAMING_CASE`.
-    (
-        @bitfield $(#[$attr:meta])* $vis:vis struct $name:ident($storage:ty) { $($fields:tt)* }
-    ) => {
-        $crate::bitfield!(
-            #[allow(non_camel_case_types)]
-            $(#[$attr])* $vis struct $name($storage) { $($fields)* }
-        );
-    };
-
-    // Implementations shared by all registers types.
-    (@io_base $name:ident($storage:ty) @ $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) => {
-        impl $crate::io::register::FixedRegister for $name {}
-
-        $(#[$attr])*
-        $vis const $name: $crate::io::register::FixedRegisterLoc<$name> =
-            $crate::io::register::FixedRegisterLoc::<$name>::new();
-    };
-
-    // Implementations of relative registers.
-    (@io_relative $name:ident @ $base:ident) => {
-        impl $crate::io::register::WithBase for $name {
-            type BaseFamily = $base;
-        }
-
-        impl $crate::io::register::RelativeRegister for $name {}
-    };
-
-    // Implementations of register arrays.
-    (@io_array $name:ident [ $size:expr, stride = $stride:expr ]) => {
-        impl $crate::io::register::Array for $name {}
-
-        impl $crate::io::register::RegisterArray for $name {
-            const SIZE: usize = $size;
-            const STRIDE: usize = $stride;
-        }
-    };
-
-    // Implementations of relative array registers.
-    (
-        @io_relative_array $name:ident [ $size:expr, stride = $stride:expr ] @ $base:ident
-    ) => {
-        impl $crate::io::register::WithBase for $name {
-            type BaseFamily = $base;
-        }
-
-        impl $crate::io::register::RegisterArray for $name {
-            const SIZE: usize = $size;
-            const STRIDE: usize = $stride;
-        }
-
-        impl $crate::io::register::RelativeRegisterArray for $name {}
+    ($($tt:tt)*) => {
+        $crate::macros::register!($($tt)*);
     };
 }