atomics: Allow architectures to define their own __atomic_op_* helpers

Some architectures may have their special barriers for acquire, release
and fence semantics, so that general memory barriers(smp_mb__*_atomic())
in the default __atomic_op_*() may be too strong, so allow architectures
to define their own helpers which can overwrite the default helpers.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index 301de78d65f75c194720cc5168359dbce6eab59f..5f3ee5a60a81a6fbb232b3cf0145cc26a34181da 100644 (file)
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -34,20 +34,29 @@
  * The idea here is to build acquire/release variants by adding explicit
  * barriers on top of the relaxed variant. In the case where the relaxed
  * variant is already fully ordered, no additional barriers are needed.
+ *
+ * Besides, if an arch has a special barrier for acquire/release, it could
+ * implement its own __atomic_op_* and use the same framework for building
+ * variants
  */
+#ifndef __atomic_op_acquire
 #define __atomic_op_acquire(op, args...)                               \
 ({                                                                     \
        typeof(op##_relaxed(args)) __ret  = op##_relaxed(args);         \
        smp_mb__after_atomic();                                         \
        __ret;                                                          \
 })
+#endif
 
+#ifndef __atomic_op_release
 #define __atomic_op_release(op, args...)                               \
 ({                                                                     \
        smp_mb__before_atomic();                                        \
        op##_relaxed(args);                                             \
 })
+#endif
 
+#ifndef __atomic_op_fence
 #define __atomic_op_fence(op, args...)                                 \
 ({                                                                     \
        typeof(op##_relaxed(args)) __ret;                               \
@@ -56,6 +65,7 @@
        smp_mb__after_atomic();                                         \
        __ret;                                                          \
 })
+#endif
 
 /* atomic_add_return_relaxed */
 #ifndef atomic_add_return_relaxed