locking/atomic, arch/avr32: Implement atomic_fetch_{add,sub,and,or,xor}()

Implement FETCH-OP atomic primitives, these are very similar to the
existing OP-RETURN primitives we already have, except they return the
value of the atomic variable _before_ modification.

This is especially useful for irreversible operations -- such as
bitops (because it becomes impossible to reconstruct the state prior
to modification).

Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Acked-by: Hans-Christian Noren Egtvedt <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Haavard Skinnemoen <[e-mail]>
Cc: Hans-Christian Egtvedt <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Paul E. McKenney <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/avr32/include/asm/atomic.h

···
 	return result;							\
 }
 
+#define ATOMIC_FETCH_OP(op, asm_op, asm_con)				\
+static inline int __atomic_fetch_##op(int i, atomic_t *v)		\
+{									\
+	int result, val;						\
+									\
+	asm volatile(							\
+		"/* atomic_fetch_" #op " */\n"				\
+		"1:	ssrf	5\n"					\
+		"	ld.w	%0, %3\n"				\
+		"	mov	%1, %0\n"				\
+		"	" #asm_op "	%1, %4\n"			\
+		"	stcond	%2, %1\n"				\
+		"	brne	1b"					\
+		: "=&r" (result), "=&r" (val), "=o" (v->counter)	\
+		: "m" (v->counter), #asm_con (i)			\
+		: "cc");						\
+									\
+	return result;							\
+}
+
 ATOMIC_OP_RETURN(sub, sub, rKs21)
 ATOMIC_OP_RETURN(add, add, r)
+ATOMIC_FETCH_OP (sub, sub, rKs21)
+ATOMIC_FETCH_OP (add, add, r)
 
-#define ATOMIC_OP(op, asm_op)						\
+#define atomic_fetch_or atomic_fetch_or
+
+#define ATOMIC_OPS(op, asm_op)						\
 ATOMIC_OP_RETURN(op, asm_op, r)						\
 static inline void atomic_##op(int i, atomic_t *v)			\
 {									\
 	(void)__atomic_##op##_return(i, v);				\
+}									\
+ATOMIC_FETCH_OP(op, asm_op, r)						\
+static inline int atomic_fetch_##op(int i, atomic_t *v)		\
+{									\
+	return __atomic_fetch_##op(i, v);				\
 }
 
-ATOMIC_OP(and, and)
-ATOMIC_OP(or, or)
-ATOMIC_OP(xor, eor)
+ATOMIC_OPS(and, and)
+ATOMIC_OPS(or, or)
+ATOMIC_OPS(xor, eor)
 
-#undef ATOMIC_OP
+#undef ATOMIC_OPS
+#undef ATOMIC_FETCH_OP
 #undef ATOMIC_OP_RETURN
 
 /*
···
 	return __atomic_add_return(i, v);
 }
 
+static inline int atomic_fetch_add(int i, atomic_t *v)
+{
+	if (IS_21BIT_CONST(i))
+		return __atomic_fetch_sub(-i, v);
+
+	return __atomic_fetch_add(i, v);
+}
+
 /*
  * atomic_sub_return - subtract the atomic variable
  * @i: integer value to subtract
···
 		return __atomic_sub_return(i, v);
 
 	return __atomic_add_return(-i, v);
+}
+
+static inline int atomic_fetch_sub(int i, atomic_t *v)
+{
+	if (IS_21BIT_CONST(i))
+		return __atomic_fetch_sub(i, v);
+
+	return __atomic_fetch_add(-i, v);
 }
 
 /*