ck_pr: Use the "dmb st" instruction on arm when available.

include/gcc/arm/ck_pr.h

@@ -54,17 +54,27 @@ ck_pr_stall(void)
 	return;
 }
 
-/* 
- * isb, dsb and dmb instructions only appeared with armv7, so use the old
- * notation
- */
+#if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__)
+#define __CK_ISB __asm __volatile("isb" : : "r" (0) : "memory")
+#define _CK_DMB __asm __volatile("dmb" : : "r" (0) : "memory")
+#define _CK_DSB __asm __volatile("dsb" : : "r" (0) : "memory")
+/* FreeBSD's toolchain doesn't accept dmb st, so use the opcode instead */
+#ifdef __FreeBSD__
+#define _CK_DMB_ST __asm __volatile(".word 0xf57ff05e" : : "r" (0) : "memory")
+#else
+#define _CK_DMB_ST __asm __volatile("dmb st" : : "r" (0) : "memory")
+#endif
 
-#define _ISB \
+#else
+/* armv6 doesn't have dsb/dmb/isb, and no way to wait only for stores */
+#define _CK_ISB \
     __asm __volatile("mcr p15, 0, %0, c7, c5, 4" : : "r" (0) : "memory")
-#define _DSB \
+#define _CK_DSB \
     __asm __volatile("mcr p15, 0, %0, c7, c10, 4" : : "r" (0) : "memory")
-#define _DMB  \
+#define _CK_DMB  \
     __asm __volatile("mcr p15, 0, %0, c7, c10, 5" : : "r" (0) : "memory")
+#define _CK_DMB_ST _CK_DMB
+#endif
 
 #define CK_PR_FENCE(T, I)				\
 	CK_CC_INLINE static void			\
@@ -73,22 +83,23 @@ ck_pr_stall(void)
 		I;					\
 	}
 
-CK_PR_FENCE(atomic, _DMB)
-CK_PR_FENCE(atomic_store, _DMB)
-CK_PR_FENCE(atomic_load, _DMB)
-CK_PR_FENCE(store_atomic, _DMB)
-CK_PR_FENCE(load_atomic, _DMB)
-CK_PR_FENCE(store, _DMB)
-CK_PR_FENCE(store_load, _DMB)
-CK_PR_FENCE(load, _DMB)
-CK_PR_FENCE(load_store, _DMB)
-CK_PR_FENCE(memory, _DMB)
+CK_PR_FENCE(atomic, _CK_DMB_ST)
+CK_PR_FENCE(atomic_store, _CK_DMB_ST)
+CK_PR_FENCE(atomic_load, _CK_DMB_ST)
+CK_PR_FENCE(store_atomic, _CK_DMB_ST)
+CK_PR_FENCE(load_atomic, _CK_DMB)
+CK_PR_FENCE(store, _CK_DMB_ST)
+CK_PR_FENCE(store_load, _CK_DMB_ST)
+CK_PR_FENCE(load, _CK_DMB)
+CK_PR_FENCE(load_store, _CK_DMB)
+CK_PR_FENCE(memory, _CK_DMB)
 
 #undef CK_PR_FENCE
 
-#undef _ISB
-#undef _DSB
-#undef _DMB
+#undef _CK_ISB
+#undef _CK_DSB
+#undef _CK_DMB
+#undef _CK_DMB_ST
 
 #define CK_PR_LOAD(S, M, T, C, I)				\
 	CK_CC_INLINE static T					\