use dmb barrier instruction for atomics on arm v7

aside from potentially offering better performance, this change is
needed since the old coprocessor-based approach to barriers is
deprecated in arm v7, and some compilers/assemblers issue errors when
using the deprecated instruction for v7 targets.

diff --git a/arch/arm/atomic.h b/arch/arm/atomic.h
index 50ad947..d8f6484 100644 (file)
--- a/arch/arm/atomic.h
+++ b/arch/arm/atomic.h
@@ -25,17 +25,24 @@ static inline int a_ctz_64(uint64_t x)
 #if __ARM_ARCH_6__ || __ARM_ARCH_6K__ || __ARM_ARCH_6ZK__ \
  || __ARM_ARCH_7A__ || __ARM_ARCH_7R__ \
  || __ARM_ARCH >= 7
+
+#if __ARM_ARCH_7A__ || __ARM_ARCH_7R__ ||  __ARM_ARCH >= 7
+#define MEM_BARRIER "dmb ish"
+#else
+#define MEM_BARRIER "mcr p15,0,r0,c7,c10,5"
+#endif
+
 static inline int __k_cas(int t, int s, volatile int *p)
 {
        int ret;
        __asm__(
-               "       mcr p15,0,r0,c7,c10,5\n"
+               "       " MEM_BARRIER "\n"
                "1:     ldrex %0,%3\n"
                "       subs %0,%0,%1\n"
                "       strexeq %0,%2,%3\n"
                "       teqeq %0,#1\n"
                "       beq 1b\n"
-               "       mcr p15,0,r0,c7,c10,5\n"
+               "       " MEM_BARRIER "\n"
                : "=&r"(ret)
                : "r"(t), "r"(s), "Q"(*p)
                : "memory", "cc" );