Index: sys/dev/ath/ah_osdep.c
===================================================================
--- sys/dev/ath/ah_osdep.c	(revision 256951)
+++ sys/dev/ath/ah_osdep.c	(working copy)
@@ -267,6 +267,7 @@
 	if (ah->ah_config.ah_serialise_reg_war)
 		mtx_lock_spin(&ah_regser_mtx);
 	bus_space_write_4(tag, h, reg, val);
+	OS_REG_WRITE_BARRIER(ah);
 	if (ah->ah_config.ah_serialise_reg_war)
 		mtx_unlock_spin(&ah_regser_mtx);
 }
@@ -333,6 +334,7 @@
 	if (ah->ah_config.ah_serialise_reg_war)
 		mtx_lock_spin(&ah_regser_mtx);
 	bus_space_write_4(tag, h, reg, val);
+	OS_REG_WRITE_BARRIER(ah);
 	if (ah->ah_config.ah_serialise_reg_war)
 		mtx_unlock_spin(&ah_regser_mtx);
 }
Index: sys/dev/ath/ah_osdep.h
===================================================================
--- sys/dev/ath/ah_osdep.h	(revision 256951)
+++ sys/dev/ath/ah_osdep.h	(working copy)
@@ -109,6 +109,21 @@
 #define	OS_REG_WRITE_BUFFER_FLUSH(_ah)		\
 	    do { } while (0)
 
+#define	OS_REG_READ_BARRIER(_ah)				\
+	bus_space_barrier((bus_space_tag_t)(_ah)->ah_st,	\
+		(bus_space_handle_t)(_ah)->ah_sh, 0, 0, 	\
+		BUS_SPACE_BARRIER_READ)
+
+#define	OS_REG_WRITE_BARRIER(_ah)				\
+	bus_space_barrier((bus_space_tag_t)(_ah)->ah_st,	\
+		(bus_space_handle_t)(_ah)->ah_sh, 0, 0, 	\
+		BUS_SPACE_BARRIER_WRITE)
+
+#define	OS_REG_RW_BARRIER(_ah)					\
+	bus_space_barrier((bus_space_tag_t)(_ah)->ah_st,	\
+		(bus_space_handle_t)(_ah)->ah_sh, 0, 0, 	\
+		BUS_SPACE_BARRIER_READ | BUS_SPACE_BARRIER_WRITE)
+
 /*
  * Register read/write operations are either handled through
  * platform-dependent routines (or when debugging is enabled
@@ -123,8 +138,12 @@
 extern	u_int32_t ath_hal_reg_read(struct ath_hal *ah, u_int reg);
 #else
 #define	OS_REG_WRITE(_ah, _reg, _val)					\
+	do {								\
 	bus_space_write_4((bus_space_tag_t)(_ah)->ah_st,		\
-	    (bus_space_handle_t)(_ah)->ah_sh, (_reg), (_val))
+	    (bus_space_handle_t)(_ah)->ah_sh, (_reg), (_val));		\
+	OS_REG_WRITE_BARRIER(_ah);					\
+	} while (0)
+
 #define	OS_REG_READ(_ah, _reg)						\
 	bus_space_read_4((bus_space_tag_t)(_ah)->ah_st,			\
 	    (bus_space_handle_t)(_ah)->ah_sh, (_reg))