diff --git a/include/asm-sh/system.h b/include/asm-sh/system.h
index eb4902e..1630a54 100644
--- a/include/asm-sh/system.h
+++ b/include/asm-sh/system.h
@@ -67,8 +67,17 @@
 {
 }
 
-#define nop() __asm__ __volatile__ ("nop")
-
+#ifdef CONFIG_CPU_SH4A
+#define __icbi()			\
+{					\
+	unsigned long __addr;		\
+	__addr = 0xa8000000;		\
+	__asm__ __volatile__(		\
+		"icbi   %0\n\t"		\
+		: /* no output */	\
+		: "m" (__m(__addr)));	\
+}
+#endif
 
 #define xchg(ptr,x) ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
 
@@ -84,15 +93,31 @@
 
 extern void __xchg_called_with_bad_pointer(void);
 
+/*
+ * A brief note on ctrl_barrier(), the control register write barrier.
+ *
+ * Legacy SH cores typically require a sequence of 8 nops after
+ * modification of a control register in order for the changes to take
+ * effect. On newer cores (like the sh4a and sh5) this is accomplished
+ * with icbi.
+ *
+ * Also note that on sh4a in the icbi case we can forego a synco for the
+ * write barrier, as it's not necessary for control registers.
+ *
+ * Historically we have only done this type of barrier for the MMUCR, but
+ * it's also necessary for the CCR, so we make it generic here instead.
+ */
 #ifdef CONFIG_CPU_SH4A
-#define mb()	__asm__ __volatile__ ("synco": : :"memory")
-#define rmb()	mb()
-#define wmb()	__asm__ __volatile__ ("synco": : :"memory")
+#define mb()		__asm__ __volatile__ ("synco": : :"memory")
+#define rmb()		mb()
+#define wmb()		__asm__ __volatile__ ("synco": : :"memory")
+#define ctrl_barrier()	__icbi()
 #define read_barrier_depends()	do { } while(0)
 #else
-#define mb()	__asm__ __volatile__ ("": : :"memory")
-#define rmb()	mb()
-#define wmb()	__asm__ __volatile__ ("": : :"memory")
+#define mb()		__asm__ __volatile__ ("": : :"memory")
+#define rmb()		mb()
+#define wmb()		__asm__ __volatile__ ("": : :"memory")
+#define ctrl_barrier()	__asm__ __volatile__ ("nop;nop;nop;nop;nop;nop;nop;nop")
 #define read_barrier_depends()	do { } while(0)
 #endif
 
@@ -218,8 +243,8 @@
 #define back_to_P1()					\
 do {							\
 	unsigned long __dummy;				\
+	ctrl_barrier();					\
 	__asm__ __volatile__(				\
-		"nop;nop;nop;nop;nop;nop;nop\n\t"	\
 		"mov.l	1f, %0\n\t"			\
 		"jmp	@%0\n\t"			\
 		" nop\n\t"				\