[PATCH v4 15/16] rust: io: register: remove `Register` trait and cleanup macro

[Gary Guo <gary@garyguo.net>]

With the removal of relative registers, there are only two type of
registers left, fixed register and register arrays. There is not much
benefit in having a common super trait for them anymore, thus remove it,
and cleanup the macro rules associated with it.

Signed-off-by: Gary Guo <gary@garyguo.net>
---
 rust/kernel/io/register.rs | 22 +++++++++++++---------
 rust/macros/io/register.rs | 12 ++++++------
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/rust/kernel/io/register.rs b/rust/kernel/io/register.rs
index 187f28f16614..9df7572aee9d 100644
--- a/rust/kernel/io/register.rs
+++ b/rust/kernel/io/register.rs
@@ -121,8 +121,8 @@
     io::IoLoc, //
 };
 
-/// Trait implemented by all registers.
-pub trait Register: Sized {
+/// Trait implemented by registers with a fixed offset.
+pub trait FixedRegister: Sized {
     /// Base type for this register.
     type Base: ?Sized;
 
@@ -132,9 +132,6 @@ pub trait Register: Sized {
     const OFFSET: usize;
 }
 
-/// Trait implemented by registers with a fixed offset.
-pub trait FixedRegister: Register {}
-
 /// Allows `()` to be used as the `location` parameter of [`Io::write`](super::Io::write) when
 /// passing a [`FixedRegister`] value.
 impl<Base: ?Sized, T> IoLoc<Base, T> for ()
@@ -201,7 +198,14 @@ fn offset(self) -> usize {
 }
 
 /// Trait implemented by arrays of registers.
-pub trait RegisterArray: Register {
+pub trait RegisterArray: Sized {
+    /// Base type for this register.
+    type Base: ?Sized;
+
+    /// Start offset of the register.
+    ///
+    /// The interpretation of this offset depends on the type of the register.
+    const OFFSET: usize;
     /// Number of elements in the registers array.
     const SIZE: usize;
     /// Number of bytes between the start of elements in the registers array.
@@ -267,8 +271,8 @@ fn try_at(idx: usize) -> Option<RegisterArrayLoc<Self>>
 ///
 /// Implementors can be used with [`Io::write_reg`](super::Io::write_reg).
 pub trait LocatedRegister<Base: ?Sized> {
-    /// Register value to write.
-    type Value: Register;
+    /// Value to write.
+    type Value;
     /// Full location information at which to write the value.
     type Location: IoLoc<Base, Self::Value>;
 
@@ -295,7 +299,7 @@ fn into_io_op(self) -> (FixedRegisterLoc<T>, T) {
 /// This is used to enforce base matching.
 #[doc(hidden)]
 #[inline(always)] // for const eval only
-pub const fn alias_offset<Base: ?Sized, Alias: Register<Base = Base>>() -> usize {
+pub const fn alias_offset<Base: ?Sized, Alias: FixedRegister<Base = Base>>() -> usize {
     Alias::OFFSET
 }
 
diff --git a/rust/macros/io/register.rs b/rust/macros/io/register.rs
index 6da8ba760ab3..7d3160c4873a 100644
--- a/rust/macros/io/register.rs
+++ b/rust/macros/io/register.rs
@@ -225,11 +225,6 @@ pub(crate) fn register(def: RegDef) -> Result<TokenStream> {
                     #[allow(non_camel_case_types)]
                     #(#attrs)* #vis struct #name(#storage) #args
                 );
-
-                impl ::kernel::io::register::Register for #name {
-                    type Base = #base;
-                    const OFFSET: usize = #offset;
-                }
             ));
         }
 
@@ -245,7 +240,10 @@ impl ::kernel::io::register::Register for #name {
             ))?,
 
             None => outputs.extend(quote_spanned!(span =>
-                impl ::kernel::io::register::FixedRegister for #name {}
+                impl ::kernel::io::register::FixedRegister for #name {
+                    type Base = #base;
+                    const OFFSET: usize = #offset;
+                }
 
                 #(#attrs)* #vis const #name: ::kernel::io::register::FixedRegisterLoc<#name> =
                     ::kernel::io::register::FixedRegisterLoc::<#name>::new();
@@ -268,6 +266,8 @@ impl ::kernel::io::register::FixedRegister for #name {}
                     impl ::kernel::io::register::Array for #name {}
 
                     impl ::kernel::io::register::RegisterArray for #name {
+                        type Base = #base;
+                        const OFFSET: usize = #offset;
                         const SIZE: usize = #size;
                         const STRIDE: usize = #stride;
                     }

-- 
2.54.0