LXR linux-old/arch/ppc64/lib/dec_and

   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
  54#endif /* ATOMIC_DEC_AND_LOCK */
  55