make atomic_read() behave consistently on avr32

@@ -16,10 +16,14 @@
 
 #include <asm/system.h>
 
-typedef struct { volatile int counter; } atomic_t;
+typedef struct { int counter; } atomic_t;
 #define ATOMIC_INIT(i)  { (i) }
 
-#define atomic_read(v)		((v)->counter)
+/*
+ * Casting to volatile here minimizes the need for barriers,
+ * without having to declare the type itself as volatile.
+ */
+#define atomic_read(v)		(*(volatile int *)&(v)->counter)
 #define atomic_set(v, i)	(((v)->counter) = i)
 
 /*