ARM: 7687/1: atomics: don't use exclusives for atomic64 read/set with LPAE

To ease page table updates with 64-bit descriptors, CPUs implementing
LPAE are required to implement ldrd/strd as atomic operations.

This patch uses these accessors instead of the exclusive variants when
performing atomic64_{read,set} on LPAE systems.
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/atomic.h

@@ -243,6 +243,29 @@ typedef struct {
 
 #define ATOMIC64_INIT(i) { (i) }
 
+#ifdef CONFIG_ARM_LPAE
+static inline u64 atomic64_read(const atomic64_t *v)
+{
+	u64 result;
+
+	__asm__ __volatile__("@ atomic64_read\n"
+"	ldrd	%0, %H0, [%1]"
+	: "=&r" (result)
+	: "r" (&v->counter), "Qo" (v->counter)
+	);
+
+	return result;
+}
+
+static inline void atomic64_set(atomic64_t *v, u64 i)
+{
+	__asm__ __volatile__("@ atomic64_set\n"
+"	strd	%2, %H2, [%1]"
+	: "=Qo" (v->counter)
+	: "r" (&v->counter), "r" (i)
+	);
+}
+#else
 static inline u64 atomic64_read(const atomic64_t *v)
 {
 	u64 result;
@@ -269,6 +292,7 @@ static inline void atomic64_set(atomic64_t *v, u64 i)
 	: "r" (&v->counter), "r" (i)
 	: "cc");
 }
+#endif
 
 static inline void atomic64_add(u64 i, atomic64_t *v)
 {