/arch/ppc64/lib/dec_and_lock.c

 1/*
 2 * ppc64 version of atomic_dec_and_lock() using cmpxchg
 3 *
 4 * This program is free software; you can redistribute it and/or
 5 * modify it under the terms of the GNU General Public License
 6 * as published by the Free Software Foundation; either version
 7 * 2 of the License, or (at your option) any later version.
 8 */
 9
10#include <linux/module.h>
11#include <linux/spinlock.h>
12#include <asm/atomic.h>
13#include <asm/system.h>
14
15/*
16 * This is an implementation of the notion of "decrement a
17 * reference count, and return locked if it decremented to zero".
18 *
19 * This implementation can be used on any architecture that
20 * has a cmpxchg, and where atomic->value is an int holding
21 * the value of the atomic (i.e. the high bits aren't used
22 * for a lock or anything like that).
23 *
24 * N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h
25 * if spinlocks are empty and thus atomic_dec_and_lock is defined
26 * to be atomic_dec_and_test - in that case we don't need it
27 * defined here as well.
28 */
29
30#ifndef ATOMIC_DEC_AND_LOCK
31int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
32{
33	int counter;
34	int newcount;
35
36	for (;;) {
37		counter = atomic_read(atomic);
38		newcount = counter - 1;
39		if (!newcount)
40			break;		/* do it the slow way */
41
42		newcount = cmpxchg(&atomic->counter, counter, newcount);
43		if (newcount == counter)
44			return 0;
45	}
46
47	spin_lock(lock);
48	if (atomic_dec_and_test(atomic))
49		return 1;
50	spin_unlock(lock);
51	return 0;
52}
53
54EXPORT_SYMBOL(_atomic_dec_and_lock);
55#endif /* ATOMIC_DEC_AND_LOCK */