[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, 31 insertions, 0 deletions

diff --git a/include/asm-arm/atomic.h b/include/asm-arm/atomic.h
index 2885972b0855..8ab1689ef56a 100644
--- a/include/asm-arm/atomic.h
+++ b/include/asm-arm/atomic.h
@@ -80,6 +80,23 @@ static inline int atomic_sub_return(int i, atomic_t *v)
         return result;
 }
 
+static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
+{
+        u32 oldval, res;
+
+        do {
+                __asm__ __volatile__("@ atomic_cmpxchg\n"
+                "ldrex  %1, [%2]\n"
+                "teq    %1, %3\n"
+                "strexeq %0, %4, [%2]\n"
+                    : "=&r" (res), "=&r" (oldval)
+                    : "r" (&ptr->counter), "Ir" (old), "r" (new)
+                    : "cc");
+        } while (res);
+
+        return oldval;
+}
+
 static inline void atomic_clear_mask(unsigned long mask, unsigned long *addr)
 {
         unsigned long tmp, tmp2;
@@ -131,6 +148,20 @@ static inline int atomic_sub_return(int i, atomic_t *v)
         return val;
 }
 
+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 long mask, unsigned long *addr)
 {
         unsigned long flags;