tools/virtio: remove smp_read_barrier_depends()

This gets rid of the last references to smp_read_barrier_depends()
 which for the kernel side was removed in v5.9. The serialization
required for Alpha is done inside READ_ONCE() instead of having
users deal with it. Simply use a full barrier, the architecture
does not have rmb in the first place.
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Message-Id: <20221128034347.990-3-dave@stgolabs.net>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

tools/virtio/ringtest/main.h

@@ -140,12 +140,6 @@ static inline void busy_wait(void)
 #define smp_wmb() smp_release()
 #endif
 
-#ifdef __alpha__
-#define smp_read_barrier_depends() smp_acquire()
-#else
-#define smp_read_barrier_depends() do {} while(0)
-#endif
-
 static __always_inline
 void __read_once_size(const volatile void *p, void *res, int size)
 {
@@ -175,13 +169,22 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 	}
 }
 
+#ifdef __alpha__
 #define READ_ONCE(x) \
 ({									\
 	union { typeof(x) __val; char __c[1]; } __u;			\
 	__read_once_size(&(x), __u.__c, sizeof(x));		\
-	smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
+	smp_mb(); /* Enforce dependency ordering from x */		\
 	__u.__val;							\
 })
+#else
+#define READ_ONCE(x)							\
+({									\
+	union { typeof(x) __val; char __c[1]; } __u;			\
+	__read_once_size(&(x), __u.__c, sizeof(x));			\
+	__u.__val;							\
+})
+#endif
 
 #define WRITE_ONCE(x, val) \
 ({							\