/*-
* Copyright (c) 1998, 1999, 2006 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Paul Kranenburg and Andrew Doran.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef _MACHINE_LOCK_H
#define _MACHINE_LOCK_H
/*
* Machine dependent spin lock operations.
*/
#if __SIMPLELOCK_UNLOCKED != 0
#error __SIMPLELOCK_UNLOCKED must be 0 for this implementation
#endif
/* XXX So we can expose this to userland. */
#ifdef __lint__
#define __ldstub(__addr) (__addr)
#else /* !__lint__ */
static __inline int __ldstub(__cpu_simple_lock_t *addr);
static __inline int __ldstub(__cpu_simple_lock_t *addr)
{
int v;
/*
* If someone else holds the lock use simple reads until it
* is released, then retry the atomic operation. This reduces
* memory bus contention because the cache-coherency logic
* does not have to broadcast invalidates on the lock while
* we spin on it.
*/
while (__ldstub(alp) != __SIMPLELOCK_UNLOCKED) {
while (*alp != __SIMPLELOCK_UNLOCKED)
/* spin */ ;
}
/*
* No memory barrier needed here to make this a load-acquire
* operation because LDSTUB already implies that. See SPARCv8
* Reference Manual, Appendix J.4 `Spin Locks', p. 271.
*/
}
#endif /* __CPU_SIMPLE_LOCK_NOINLINE */
static __inline int
__cpu_simple_lock_try(__cpu_simple_lock_t *alp)
{
/*
* No memory barrier needed for LDSTUB to be a load-acquire --
* see __cpu_simple_lock.
*/
return (__ldstub(alp) == __SIMPLELOCK_UNLOCKED);
}
/*
* Insert compiler barrier to prevent instruction re-ordering
* around the lock release.
*
* No memory barrier needed because we run the kernel in TSO.
* If we ran the kernel in PSO, this would require STBAR.
*/
__insn_barrier();
*alp = __SIMPLELOCK_UNLOCKED;
}
