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/* $OpenBSD: _atomic_lock.c,v 1.2 2006/01/05 22:33:24 marc Exp $ */
/*
* Atomic lock for mips
*/
#include <spinlock.h>
int
_atomic_lock(volatile _spinlock_lock_t *lock)
{
_spinlock_lock_t old;
_spinlock_lock_t temp;
do {
/*
* On a mips2 machine and above, we can use ll/sc.
* Read the lock and tag the cache line with a 'load linked'
* instruction. (Register 17 (LLAddr) will hold the
* physical address of lock for diagnostic purposes);
* (Under pathologically heavy swapping, the physaddr may
* change! XXX)
*/
__asm__("ll %0, %1" : "=r"(old) : "m"(*lock));
if (old != _SPINLOCK_UNLOCKED)
break; /* already locked */
/*
* Try and store a 1 at the tagged lock address. If
* anyone else has since written it, the tag on the cache
* line will have been wiped, and temp will be set to zero
* by the 'store conditional' instruction.
*/
temp = _SPINLOCK_LOCKED;
__asm__("sc %0, %1" : "=r"(temp), "=m"(*lock)
: "0"(temp));
} while (temp == _SPINLOCK_UNLOCKED);
return (old != _SPINLOCK_UNLOCKED);
}
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