1 files changed, 13 insertions, 11 deletions

diff --git a/arch/powerpc/include/asm/system.h b/arch/powerpc/include/asm/system.h
index d6648c14332..2a4be19a92c 100644
--- a/arch/powerpc/include/asm/system.h
+++ b/arch/powerpc/include/asm/system.h
@@ -23,15 +23,17 @@
  * read_barrier_depends() prevents data-dependent loads being reordered
  *      across this point (nop on PPC).
  *
- * We have to use the sync instructions for mb(), since lwsync doesn't
- * order loads with respect to previous stores.  Lwsync is fine for
- * rmb(), though. Note that rmb() actually uses a sync on 32-bit
- * architectures.
+ * *mb() variants without smp_ prefix must order all types of memory
+ * operations with one another. sync is the only instruction sufficient
+ * to do this.
  *
- * For wmb(), we use sync since wmb is used in drivers to order
- * stores to system memory with respect to writes to the device.
- * However, smp_wmb() can be a lighter-weight lwsync or eieio barrier
- * on SMP since it is only used to order updates to system memory.
+ * For the smp_ barriers, ordering is for cacheable memory operations
+ * only. We have to use the sync instruction for smp_mb(), since lwsync
+ * doesn't order loads with respect to previous stores.  Lwsync can be
+ * used for smp_rmb() and smp_wmb().
+ *
+ * However, on CPUs that don't support lwsync, lwsync actually maps to a
+ * heavy-weight sync, so smp_wmb() can be a lighter-weight eieio.
  */
 #define mb()   __asm__ __volatile__ ("sync" : : : "memory")
 #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
@@ -45,14 +47,14 @@
 #ifdef CONFIG_SMP
 
 #ifdef __SUBARCH_HAS_LWSYNC
-#    define SMPWMB      lwsync
+#    define SMPWMB      LWSYNC
 #else
 #    define SMPWMB      eieio
 #endif
 
 #define smp_mb()        mb()
-#define smp_rmb()       rmb()
-#define smp_wmb()       __asm__ __volatile__ (__stringify(SMPWMB) : : :"memory")
+#define smp_rmb()       __asm__ __volatile__ (stringify_in_c(LWSYNC) : : :"memory")
+#define smp_wmb()       __asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
 #define smp_read_barrier_depends()      read_barrier_depends()
 #else
 #define smp_mb()        barrier()