linux/include/asm-powerpc/semaphore.h

#ifndef _ASM_POWERPC_SEMAPHORE_H
#define _ASM_POWERPC_SEMAPHORE_H

/*
 * Remove spinlock-based RW semaphores; RW semaphore definitions are
 * now in rwsem.h and we use the generic lib/rwsem.c implementation.
 * Rework semaphores to use atomic_dec_if_positive.
 * -- Paul Mackerras (paulus@samba.org)
 */

#ifdef __KERNEL__

#include <asm/atomic.h>
#include <asm/system.h>
#include <linux/wait.h>
#include <linux/rwsem.h>

struct semaphore {
	/*
	 * Note that any negative value of count is equivalent to 0,
	 * but additionally indicates that some process(es) might be
	 * sleeping on `wait'.
	 */
	atomic_t count;
	wait_queue_head_t wait;
};

#define __SEMAPHORE_INITIALIZER(name, n)				\
{									\
	.count		= ATOMIC_INIT(n),				\
	.wait		= __WAIT_QUEUE_HEAD_INITIALIZER((name).wait)	\
}

#define __DECLARE_SEMAPHORE_GENERIC(name, count) \
	struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)

#define DECLARE_MUTEX(name)		__DECLARE_SEMAPHORE_GENERIC(name, 1)
#define DECLARE_MUTEX_LOCKED(name)	__DECLARE_SEMAPHORE_GENERIC(name, 0)

static inline void sema_init (struct semaphore *sem, int val)
{
	atomic_set(&sem->count, val);
	init_waitqueue_head(&sem->wait);
}

static inline void init_MUTEX (struct semaphore *sem)
{
	sema_init(sem, 1);
}

static inline void init_MUTEX_LOCKED (struct semaphore *sem)
{
	sema_init(sem, 0);
}

extern void __down(struct semaphore * sem);
extern int  __down_interruptible(struct semaphore * sem);
extern void __up(struct semaphore * sem);

static inline void down(struct semaphore * sem)
{
	might_sleep();

	/*
	 * Try to get the semaphore, take the slow path if we fail.
	 */
	if (unlikely(atomic_dec_return(&sem->count) < 0))
		__down(sem);
}

static inline int down_interruptible(struct semaphore * sem)
{
	int ret = 0;

	might_sleep();

	if (unlikely(atomic_dec_return(&sem->count) < 0))
		ret = __down_interruptible(sem);
	return ret;
}

static inline int down_trylock(struct semaphore * sem)
{
	return atomic_dec_if_positive(&sem->count) < 0;
}

static inline void up(struct semaphore * sem)
{
	if (unlikely(atomic_inc_return(&sem->count) <= 0))
		__up(sem);
}

#endif /* __KERNEL__ */

#endif /* _ASM_POWERPC_SEMAPHORE_H */