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lock.h revision 1.14 
      1 /*	$NetBSD: lock.h,v 1.14 2003/12/26 06:00:58 mrg Exp $ */
      2 
      3 /*-
      4  * Copyright (c) 1998, 1999 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Paul Kranenburg.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *        This product includes software developed by the NetBSD
     21  *        Foundation, Inc. and its contributors.
     22  * 4. Neither the name of The NetBSD Foundation nor the names of its
     23  *    contributors may be used to endorse or promote products derived
     24  *    from this software without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     27  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     28  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     29  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     30  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     31  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     32  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     33  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     34  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     35  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     36  * POSSIBILITY OF SUCH DAMAGE.
     37  */
     38 
     39 #ifndef _MACHINE_LOCK_H
     40 #define _MACHINE_LOCK_H
     41 
     42 /*
     43  * Machine dependent spin lock operations.
     44  */
     45 
     46 /* XXX So we can expose this to userland. */
     47 #ifdef __lint__
     48 #define __ldstub(__addr)	(__addr)
     49 #else /* !__lint__ */
     50 static __inline__ int __ldstub(__cpu_simple_lock_t *addr);
     51 static __inline__ int __ldstub(__cpu_simple_lock_t *addr)
     52 {
     53 	int v;
     54 
     55 	__asm __volatile("ldstub [%1],%0"
     56 	    : "=r" (v)
     57 	    : "r" (addr)
     58 	    : "memory");
     59 
     60 	return v;
     61 }
     62 #endif /* __lint__ */
     63 
     64 static __inline void __cpu_simple_lock_init __P((__cpu_simple_lock_t *))
     65 	__attribute__((__unused__));
     66 static __inline void __cpu_simple_lock __P((__cpu_simple_lock_t *))
     67 	__attribute__((__unused__));
     68 static __inline int __cpu_simple_lock_try __P((__cpu_simple_lock_t *))
     69 	__attribute__((__unused__));
     70 static __inline void __cpu_simple_unlock __P((__cpu_simple_lock_t *))
     71 	__attribute__((__unused__));
     72 
     73 #if __SIMPLELOCK_UNLOCKED != 0
     74 #error __SIMPLELOCK_UNLOCKED must be 0 for this implementation
     75 #endif
     76 
     77 static __inline void
     78 __cpu_simple_lock_init(__cpu_simple_lock_t *alp)
     79 {
     80 
     81 	*alp = __SIMPLELOCK_UNLOCKED;
     82 }
     83 
     84 static __inline void
     85 __cpu_simple_lock(__cpu_simple_lock_t *alp)
     86 {
     87 
     88 	/*
     89 	 * If someone else holds the lock use simple reads until it
     90 	 * is released, then retry the atomic operation. This reduces
     91 	 * memory bus contention because the cache-coherency logic
     92 	 * does not have to broadcast invalidates on the lock while
     93 	 * we spin on it.
     94 	 */
     95 	while (__ldstub(alp) != __SIMPLELOCK_UNLOCKED) {
     96 		while (*alp != __SIMPLELOCK_UNLOCKED)
     97 			/* spin */ ;
     98 	}
     99 }
    100 
    101 static __inline int
    102 __cpu_simple_lock_try(__cpu_simple_lock_t *alp)
    103 {
    104 
    105 	return (__ldstub(alp) == __SIMPLELOCK_UNLOCKED);
    106 }
    107 
    108 static __inline void
    109 __cpu_simple_unlock(__cpu_simple_lock_t *alp)
    110 {
    111 
    112 	/*
    113 	 * Insert compiler barrier to prevent instruction re-ordering
    114 	 * around the lock release.
    115 	 */
    116 	__insn_barrier();
    117 	*alp = __SIMPLELOCK_UNLOCKED;
    118 }
    119 
    120 #endif /* _MACHINE_LOCK_H */
    121