linux-kernel - [RFC v2 2/7] atomics: Allow architectures to define their own __atomic_op

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Message-Id: <1442418575-12297-3-git-send-email-boqun.feng@gmail.com>
Date:	Wed, 16 Sep 2015 23:49:30 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@...com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [RFC v2 2/7] 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@...il.com>
---
 include/linux/atomic.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index 00a5763..590c023 100644
--- 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
-- 
2.5.1

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