[PATCH 19/24] make atomic_read() behave consistently on sparc64

[Chris Snook <csnook@redhat.com>]

From: Chris Snook <csnook@redhat.com>

Purify volatile use for atomic[64]_t on sparc64.

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

--- linux-2.6.23-rc2-orig/include/asm-sparc64/atomic.h	2007-07-08 19:32:17.000000000 -0400
+++ linux-2.6.23-rc2/include/asm-sparc64/atomic.h	2007-08-09 07:48:01.000000000 -0400
@@ -11,14 +11,18 @@
 #include <linux/types.h>
 #include <asm/system.h>
 
-typedef struct { volatile int counter; } atomic_t;
-typedef struct { volatile __s64 counter; } atomic64_t;
+typedef struct { int counter; } atomic_t;
+typedef struct { __s64 counter; } atomic64_t;
 
 #define ATOMIC_INIT(i)		{ (i) }
 #define ATOMIC64_INIT(i)	{ (i) }
 
-#define atomic_read(v)		((v)->counter)
-#define atomic64_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 atomic64_read(v)	(*(volatile __s64 *)&(v)->counter)
 
 #define atomic_set(v, i)	(((v)->counter) = i)
 #define atomic64_set(v, i)	(((v)->counter) = i)