[PATCH] mutex subsystem, add include/asm-arm/mutex.h

/*

 * include/asm-arm/mutex.h

 *

 * ARM optimized mutex locking primitives

 *

 * Please look into asm-generic/mutex-xchg.h for a formal definition.

 */

#ifndef _ASM_MUTEX_H

#define _ASM_MUTEX_H

#if __LINUX_ARM_ARCH__ < 6

/* On pre-ARMv6 hardware the swp based implementation is the most efficient. */

# include <asm-generic/mutex-xchg.h>

#else

/*

 * Attempting to lock a mutex on ARMv6+ can be done with a bastardized

 * atomic decrement (it is not a reliable atomic decrement but it satisfies

 * the defined semantics for our purpose, while being smaller and faster

 * than a real atomic decrement or atomic swap.  The idea is to attempt

 * decrementing the lock value only once.  If once decremented it isn't zero,

 * or if its store-back fails due to a dispute on the exclusive store, we

 * simply bail out immediately through the slow path where the lock will be

 * reattempted until it succeeds.

 */

#define __mutex_fastpath_lock(count, fail_fn)				\

do {									\

	int __ex_flag, __res;						\

									\

	typecheck(atomic_t *, count);					\

	typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);		\

									\

	__asm__ (							\

		"ldrex	%0, [%2]	\n"				\

		"sub	%0, %0, #1	\n"				\

		"strex	%1, %0, [%2]	\n"				\

									\

		: "=&r" (__res), "=&r" (__ex_flag)			\

		: "r" (&(count)->counter)				\

		: "cc","memory" );					\

									\

	if (unlikely(__res || __ex_flag))				\

		fail_fn(count);						\

} while (0)

#define __mutex_fastpath_lock_retval(count, fail_fn)			\

({									\

	int __ex_flag, __res;						\

									\

	typecheck(atomic_t *, count);					\

	typecheck_fn(fastcall int (*)(atomic_t *), fail_fn);		\

									\

	__asm__ (							\

		"ldrex	%0, [%2]	\n"				\

		"sub	%0, %0, #1	\n"				\

		"strex	%1, %0, [%2]	\n"				\

									\

		: "=&r" (__res), "=&r" (__ex_flag)			\

		: "r" (&(count)->counter)				\

		: "cc","memory" );					\

									\

	__res |= __ex_flag;						\

	if (unlikely(__res != 0))					\

		__res = fail_fn(count);					\

	__res;								\

})

/*

 * Same trick is used for the unlock fast path. However the original value,

 * rather than the result, is used to test for success in order to have

 * better generated assembly.

 */

#define __mutex_fastpath_unlock(count, fail_fn)				\

do {									\

	int __ex_flag, __res, __orig;					\

									\

	typecheck(atomic_t *, count);					\

	typecheck_fn(fastcall void (*)(atomic_t *), fail_fn);		\

									\

	__asm__ (							\

		"ldrex	%0, [%3]	\n"				\

		"add	%1, %0, #1	\n"				\

		"strex	%2, %1, [%3]	\n"				\

									\

		: "=&r" (__orig), "=&r" (__res), "=&r" (__ex_flag)	\

		: "r" (&(count)->counter)				\

		: "cc","memory" );					\

									\

	if (unlikely(__orig || __ex_flag))				\

		fail_fn(count);						\

} while (0)

/*

 * If the unlock was done on a contended lock, or if the unlock simply fails

 * then the mutex remains locked.

 */

#define __mutex_slowpath_needs_to_unlock()	1

/*

 * For __mutex_fastpath_trylock we use another construct which could be

 * described as a "single value cmpxchg".

 *

 * This provides the needed trylock semantics like cmpxchg would, but it is

 * lighter and less generic than a true cmpxchg implementation.

 */

static inline int

__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))

{

	int __ex_flag, __res, __orig;

	__asm__ (

		"1: ldrex	%0, [%3]	\n"

		"subs		%1, %0, #1	\n"

		"strexeq	%2, %1, [%3]	\n"

		"movlt		%0, #0		\n"

		"cmpeq		%2, #0		\n"

		"bgt		1b		\n"

		: "=&r" (__orig), "=&r" (__res), "=&r" (__ex_flag)

		: "r" (&count->counter)

		: "cc", "memory" );

	return __orig;

}

#endif

#endif