[WIP 2/3] rust: atomic: Add ARM64 fetch_add_relaxed()

[Boqun Feng <boqun.feng@xxxxxxxxx>]

Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
 rust/kernel/sync/atomic/arch.rs       |  6 ++++++
 rust/kernel/sync/atomic/arch/arm64.rs | 26 ++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 rust/kernel/sync/atomic/arch/arm64.rs

diff --git a/rust/kernel/sync/atomic/arch.rs b/rust/kernel/sync/atomic/arch.rs
index 3eb5a103a69a..fc280f229237 100644
--- a/rust/kernel/sync/atomic/arch.rs
+++ b/rust/kernel/sync/atomic/arch.rs
@@ -5,5 +5,11 @@
 #[cfg(CONFIG_X86)]
 pub(crate) use x86::*;
 
+#[cfg(CONFIG_ARM64)]
+pub(crate) use arm64::*;
+
 #[cfg(CONFIG_X86)]
 pub(crate) mod x86;
+
+#[cfg(CONFIG_ARM64)]
+pub(crate) mod arm64;
diff --git a/rust/kernel/sync/atomic/arch/arm64.rs b/rust/kernel/sync/atomic/arch/arm64.rs
new file mode 100644
index 000000000000..438f37cf7df6
--- /dev/null
+++ b/rust/kernel/sync/atomic/arch/arm64.rs
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! ARM64 implementation for atomic and barrier primitives.
+
+use core::arch::asm;
+use core::cell::UnsafeCell;
+
+pub(crate) fn i32_fetch_add_relaxed(v: &UnsafeCell<i32>, i: i32) -> i32 {
+    let mut result;
+    unsafe {
+        asm!(
+            "prfm    pstl1strm, [{v}]",
+            "1: ldxr {result:w}, [{v}]",
+            "add {val:w}, {result:w}, {i:w}",
+            "stxr {tmp:w}, {val:w}, [{v}]",
+            "cbnz {tmp:w}, 1b",
+            result = out(reg) result,
+            tmp = out(reg) _,
+            val = out(reg) _,
+            v = in(reg) v.get(),
+            i = in(reg) i,
+        )
+    }
+
+    result
+}
-- 
2.44.0