rust: helpers: Add i8/i16 atomic_read_acquire/atomic_set_release helpers

Add helper functions to expose smp_load_acquire() and
smp_store_release() for i8 and i16 types.

The smp_load_acquire() and smp_store_release() macros require type
information (sizeof) to generate appropriate architecture-specific
memory ordering instructions. Therefore, separate helper functions are
needed for each type size.

These helpers expose different symbol names than their C counterparts
so they are split into atomic_ext.c instead of atomic.c. The symbol
names; atomic_[i8|i16]_read_acquire and atomic_[i8|i16]_set_release
makes the interface Rust/C clear, consistent with i32/i64.

These helpers will be used by the upcoming Atomic<i8> and Atomic<i16>
implementation to provide proper Acquire/Release semantics across all
architectures.

[boqun: Rename the functions from {load,store} to {read,set} to avoid
future adjustment]

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://patch.msgid.link/20251211113826.1299077-2-fujita.tomonori@gmail.com

rust/helpers/atomic_ext.c

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <asm/barrier.h>
+
+__rust_helper s8 rust_helper_atomic_i8_read_acquire(s8 *ptr)
+{
+	return smp_load_acquire(ptr);
+}
+
+__rust_helper s16 rust_helper_atomic_i16_read_acquire(s16 *ptr)
+{
+	return smp_load_acquire(ptr);
+}
+
+__rust_helper void rust_helper_atomic_i8_set_release(s8 *ptr, s8 val)
+{
+	smp_store_release(ptr, val);
+}
+
+__rust_helper void rust_helper_atomic_i16_set_release(s16 *ptr, s16 val)
+{
+	smp_store_release(ptr, val);
+}

rust/helpers/helpers.c

@@ -8,6 +8,7 @@
  */
 
 #include "atomic.c"
+#include "atomic_ext.c"
 #include "auxiliary.c"
 #include "barrier.c"
 #include "binder.c"