From: FUJITA Tomonori <fujita.tomonori@gmail.com>
Date: Thu, 21 Aug 2025 00:20:54 +0000 (+0900)
Subject: rust: Add cpu_relax() helper
X-Git-Tag: v6.18-rc1~172^2~28
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=842aedc3907deb154eedb88c7e4c3278c9b33701;p=thirdparty%2Fkernel%2Flinux.git

rust: Add cpu_relax() helper

Add cpu_relax() helper in preparation for supporting
read_poll_timeout().

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Link: https://lore.kernel.org/r/20250821002055.3654160-2-fujita.tomonori@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---

diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 44b2005d50140..a90a87cff38c7 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -35,6 +35,7 @@
 #include "pid_namespace.c"
 #include "platform.c"
 #include "poll.c"
+#include "processor.c"
 #include "property.c"
 #include "rbtree.c"
 #include "rcu.c"
diff --git a/rust/helpers/processor.c b/rust/helpers/processor.c
new file mode 100644
index 0000000000000..d41355e14d6eb
--- /dev/null
+++ b/rust/helpers/processor.c
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/processor.h>
+
+void rust_helper_cpu_relax(void)
+{
+	cpu_relax();
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index f8db761c5c95f..953a6cba501cb 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -111,6 +111,7 @@ pub mod pid_namespace;
 pub mod platform;
 pub mod prelude;
 pub mod print;
+pub mod processor;
 pub mod rbtree;
 pub mod regulator;
 pub mod revocable;
diff --git a/rust/kernel/processor.rs b/rust/kernel/processor.rs
new file mode 100644
index 0000000000000..85b49b3614dd2
--- /dev/null
+++ b/rust/kernel/processor.rs
@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Processor related primitives.
+//!
+//! C header: [`include/linux/processor.h`](srctree/include/linux/processor.h)
+
+/// Lower CPU power consumption or yield to a hyperthreaded twin processor.
+///
+/// It also happens to serve as a compiler barrier.
+#[inline]
+pub fn cpu_relax() {
+    // SAFETY: Always safe to call.
+    unsafe { bindings::cpu_relax() }
+}