FRV: Don't make smp_{r, w, }mb() interpolate MEMBAR when CONFIG_SMP=n [try #2]

Don't make smp_{r,w,}mb() interpolate a MEMBAR instruction when CONFIG_SMP=n as
SMP memory barries on UP systems should interpolate a compiler barrier only.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-frv/system.h

@@ -179,14 +179,23 @@ do {							\
 #define mb()			asm volatile ("membar" : : :"memory")
 #define rmb()			asm volatile ("membar" : : :"memory")
 #define wmb()			asm volatile ("membar" : : :"memory")
-#define set_mb(var, value)	do { var = value; mb(); } while (0)
+#define read_barrier_depends()	barrier()
 
+#ifdef CONFIG_SMP
 #define smp_mb()			mb()
 #define smp_rmb()			rmb()
 #define smp_wmb()			wmb()
-
-#define read_barrier_depends()		do {} while(0)
 #define smp_read_barrier_depends()	read_barrier_depends()
+#define set_mb(var, value) \
+	do { xchg(&var, (value)); } while (0)
+#else
+#define smp_mb()			barrier()
+#define smp_rmb()			barrier()
+#define smp_wmb()			barrier()
+#define smp_read_barrier_depends()	do {} while(0)
+#define set_mb(var, value) \
+	do { var = (value); barrier(); } while (0)
+#endif
 
 #define HARD_RESET_NOW()			\
 do {						\