[PATCH] atomic: cmpxchg

Introduce an atomic_cmpxchg operation.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/asm-sh/atomic.h b/include/asm-sh/atomic.h
index 3c4f805da1ac..a148c762d366 100644
--- a/include/asm-sh/atomic.h
+++ b/include/asm-sh/atomic.h
@@ -87,6 +87,20 @@ static __inline__ int atomic_sub_return(int i, atomic_t * v)
 #define atomic_inc(v) atomic_add(1,(v))
 #define atomic_dec(v) atomic_sub(1,(v))
 
+static inline int atomic_cmpxchg(atomic_t *v, int old, int new)
+{
+        int ret;
+        unsigned long flags;
+
+        local_irq_save(flags);
+        ret = v->counter;
+        if (likely(ret == old))
+                v->counter = new;
+        local_irq_restore(flags);
+
+        return ret;
+}
+
 static __inline__ void atomic_clear_mask(unsigned int mask, atomic_t *v)
 {
         unsigned long flags;