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lock.h revision 1.20 
      1 /*	$NetBSD: lock.h,v 1.20 2005/12/24 20:07:32 perry 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 #if __SIMPLELOCK_UNLOCKED != 0
     47 #error __SIMPLELOCK_UNLOCKED must be 0 for this implementation
     48 #endif
     49 
     50 /* XXX So we can expose this to userland. */
     51 #ifdef __lint__
     52 #define __ldstub(__addr)	(__addr)
     53 #else /* !__lint__ */
     54 static __inline__ int __ldstub(__cpu_simple_lock_t *addr);
     55 static __inline__ int __ldstub(__cpu_simple_lock_t *addr)
     56 {
     57 	int v;
     58 
     59 	__asm volatile("ldstub [%1],%0"
     60 	    : "=&r" (v)
     61 	    : "r" (addr)
     62 	    : "memory");
     63 
     64 	return v;
     65 }
     66 #endif /* __lint__ */
     67 
     68 static inline void __cpu_simple_lock_init __P((__cpu_simple_lock_t *))
     69 	__attribute__((__unused__));
     70 static inline int __cpu_simple_lock_try __P((__cpu_simple_lock_t *))
     71 	__attribute__((__unused__));
     72 static inline void __cpu_simple_unlock __P((__cpu_simple_lock_t *))
     73 	__attribute__((__unused__));
     74 #ifndef __CPU_SIMPLE_LOCK_NOINLINE
     75 static inline void __cpu_simple_lock __P((__cpu_simple_lock_t *))
     76 	__attribute__((__unused__));
     77 #else
     78 extern void __cpu_simple_lock __P((__cpu_simple_lock_t *));
     79 #endif
     80 
     81 static inline void
     82 __cpu_simple_lock_init(__cpu_simple_lock_t *alp)
     83 {
     84 
     85 	*alp = __SIMPLELOCK_UNLOCKED;
     86 }
     87 
     88 #ifndef __CPU_SIMPLE_LOCK_NOINLINE
     89 static inline void
     90 __cpu_simple_lock(__cpu_simple_lock_t *alp)
     91 {
     92 
     93 	/*
     94 	 * If someone else holds the lock use simple reads until it
     95 	 * is released, then retry the atomic operation. This reduces
     96 	 * memory bus contention because the cache-coherency logic
     97 	 * does not have to broadcast invalidates on the lock while
     98 	 * we spin on it.
     99 	 */
    100 	while (__ldstub(alp) != __SIMPLELOCK_UNLOCKED) {
    101 		while (*alp != __SIMPLELOCK_UNLOCKED)
    102 			/* spin */ ;
    103 	}
    104 }
    105 #endif /* __CPU_SIMPLE_LOCK_NOINLINE */
    106 
    107 static inline int
    108 __cpu_simple_lock_try(__cpu_simple_lock_t *alp)
    109 {
    110 
    111 	return (__ldstub(alp) == __SIMPLELOCK_UNLOCKED);
    112 }
    113 
    114 static inline void
    115 __cpu_simple_unlock(__cpu_simple_lock_t *alp)
    116 {
    117 
    118 	/*
    119 	 * Insert compiler barrier to prevent instruction re-ordering
    120 	 * around the lock release.
    121 	 */
    122 	__insn_barrier();
    123 	*alp = __SIMPLELOCK_UNLOCKED;
    124 }
    125 
    126 #endif /* _MACHINE_LOCK_H */
    127