Add cmpxchg64 and cmpxchg64_local to mips

Make sure that at least cmpxchg64_local is available on all architectures to use
for unsigned long long values.

Signed-off-by: Mathieu Desnoyers <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/asm-mips/cmpxchg.h

···
 #define cmpxchg(ptr, old, new)		__cmpxchg(ptr, old, new, smp_llsc_mb())
 #define cmpxchg_local(ptr, old, new)	__cmpxchg(ptr, old, new, )
 
+#define cmpxchg64(ptr, o, n)						\
+  ({									\
+	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
+	cmpxchg((ptr), (o), (n));					\
+  })
+
+#ifdef CONFIG_64BIT
+#define cmpxchg64_local(ptr, o, n)					\
+  ({									\
+	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
+	cmpxchg_local((ptr), (o), (n));					\
+  })
+#else
+#include <asm-generic/cmpxchg-local.h>
+#define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
+#endif
+
 #endif /* __ASM_CMPXCHG_H */