locking/atomic: openrisc: avoid asm-generic/atomic.h

OpenRISC is the only architecture which uses asm-generic/atomic.h and
also provides its own implementation of some functions, requiring
ifdeferry in the asm-generic header. As OpenRISC provides the vast
majority of functions itself, it would be simpler overall if it also
provided the few functions it cribs from asm-generic.

This patch decouples OpenRISC from asm-generic/atomic.h. Subsequent
patches will simplify the asm-generic implementation and remove the now
unnecessary ifdeferry.

There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Stafford Horne <shorne@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210525140232.53872-6-mark.rutland@arm.com

arch/openrisc/include/asm/atomic.h

@@ -121,6 +121,12 @@ static inline int atomic_fetch_add_unless(atomic_t *v, int a, int u)
 }
 #define atomic_fetch_add_unless	atomic_fetch_add_unless
 
-#include <asm-generic/atomic.h>
+#define atomic_read(v)			READ_ONCE((v)->counter)
+#define atomic_set(v,i)			WRITE_ONCE((v)->counter, (i))
+
+#include <asm/cmpxchg.h>
+
+#define atomic_xchg(ptr, v)		(xchg(&(ptr)->counter, (v)))
+#define atomic_cmpxchg(v, old, new)	(cmpxchg(&((v)->counter), (old), (new)))
 
 #endif /* __ASM_OPENRISC_ATOMIC_H */