aboutsummaryrefslogtreecommitdiff
path: root/arch/ppc/lib/dec_and_lock.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/ppc/lib/dec_and_lock.c')
-rw-r--r--arch/ppc/lib/dec_and_lock.c46
1 files changed, 46 insertions, 0 deletions
diff --git a/arch/ppc/lib/dec_and_lock.c b/arch/ppc/lib/dec_and_lock.c
new file mode 100644
index 00000000000..4ee888070d9
--- /dev/null
+++ b/arch/ppc/lib/dec_and_lock.c
@@ -0,0 +1,46 @@
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <asm/atomic.h>
+#include <asm/system.h>
+
+/*
+ * This is an implementation of the notion of "decrement a
+ * reference count, and return locked if it decremented to zero".
+ *
+ * This implementation can be used on any architecture that
+ * has a cmpxchg, and where atomic->value is an int holding
+ * the value of the atomic (i.e. the high bits aren't used
+ * for a lock or anything like that).
+ *
+ * N.B. ATOMIC_DEC_AND_LOCK gets defined in include/linux/spinlock.h
+ * if spinlocks are empty and thus atomic_dec_and_lock is defined
+ * to be atomic_dec_and_test - in that case we don't need it
+ * defined here as well.
+ */
+
+#ifndef ATOMIC_DEC_AND_LOCK
+int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
+{
+ int counter;
+ int newcount;
+
+ for (;;) {
+ counter = atomic_read(atomic);
+ newcount = counter - 1;
+ if (!newcount)
+ break; /* do it the slow way */
+
+ newcount = cmpxchg(&atomic->counter, counter, newcount);
+ if (newcount == counter)
+ return 0;
+ }
+
+ spin_lock(lock);
+ if (atomic_dec_and_test(atomic))
+ return 1;
+ spin_unlock(lock);
+ return 0;
+}
+
+EXPORT_SYMBOL(_atomic_dec_and_lock);
+#endif /* ATOMIC_DEC_AND_LOCK */