[PATCH 15/24] make atomic_read() behave consistently on powerpc

[PATCH 15/24] make atomic_read() behave consistently on powerpc

[Chris Snook]

From: Chris Snook <csnook@redhat.com>

Purify volatile use for atomic[64]_t on powerpc.

Signed-off-by: Chris Snook <csnook@redhat.com>

--- linux-2.6.23-rc2-orig/include/asm-powerpc/atomic.h	2007-07-08 19:32:17.000000000 -0400
+++ linux-2.6.23-rc2/include/asm-powerpc/atomic.h	2007-08-09 07:15:21.000000000 -0400
@@ -5,7 +5,7 @@
  * PowerPC atomic operations
  */
 
-typedef struct { volatile int counter; } atomic_t;
+typedef struct { int counter; } atomic_t;
 
 #ifdef __KERNEL__
 #include <linux/compiler.h>
@@ -15,7 +15,11 @@ typedef struct { volatile int counter; }
 
 #define ATOMIC_INIT(i)		{ (i) }
 
-#define atomic_read(v)		((v)->counter)
+/*
+ * Casting to volatile here minimizes the need for barriers,
+ * without having to declare the type itself as volatile.
+ */
+#define atomic_read(v)		(*(volatile int *)&(v)->counter)
 #define atomic_set(v,i)		(((v)->counter) = (i))
 
 static __inline__ void atomic_add(int a, atomic_t *v)
@@ -240,11 +244,11 @@ static __inline__ int atomic_dec_if_posi
 
 #ifdef __powerpc64__
 
-typedef struct { volatile long counter; } atomic64_t;
+typedef struct { long counter; } atomic64_t;
 
 #define ATOMIC64_INIT(i)	{ (i) }
 
-#define atomic64_read(v)	((v)->counter)
+#define atomic64_read(v)	(*(volatile long *)&(v)->counter)
 #define atomic64_set(v,i)	(((v)->counter) = (i))
 
 static __inline__ void atomic64_add(long a, atomic64_t *v)