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lock.h revision 1.8.16.1 
      1 /*	$NetBSD: lock.h,v 1.8.16.1 2002/03/19 05:15:35 thorpej Exp $ */
      2 
      3 /*-
      4  * Copyright (c) 1998, 1999, 2002 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 /*
     47  * The value for __SIMPLELOCK_LOCKED is what ldstub() naturally stores.
     48  */
     49 
     50 typedef	__volatile unsigned char __cpu_simple_lock_t;
     51 
     52 #define	__SIMPLELOCK_LOCKED	0xff
     53 #define	__SIMPLELOCK_UNLOCKED	0
     54 
     55 /* XXX So we can expose this to userland. */
     56 #ifdef __lint__
     57 #define __ldstub(__addr)	(__addr)
     58 #else /* !__lint__ */
     59 #define	__ldstub(__addr)						\
     60 ({									\
     61 	int __v;							\
     62 									\
     63 	__asm __volatile("ldstub [%1],%0"				\
     64 	    : "=r" (__v)						\
     65 	    : "r" (__addr)						\
     66 	    : "memory");						\
     67 									\
     68 	__v;								\
     69 })
     70 #endif /* __lint__ */
     71 
     72 static __inline void __cpu_simple_lock_init __P((__cpu_simple_lock_t *))
     73 	__attribute__((__unused__));
     74 static __inline void __cpu_simple_lock __P((__cpu_simple_lock_t *))
     75 	__attribute__((__unused__));
     76 static __inline int __cpu_simple_lock_try __P((__cpu_simple_lock_t *))
     77 	__attribute__((__unused__));
     78 static __inline void __cpu_simple_unlock __P((__cpu_simple_lock_t *))
     79 	__attribute__((__unused__));
     80 
     81 static __inline void
     82 __cpu_simple_lock_init(__cpu_simple_lock_t *alp)
     83 {
     84 
     85 	*alp = __SIMPLELOCK_UNLOCKED;
     86 }
     87 
     88 static __inline void
     89 __cpu_simple_lock(__cpu_simple_lock_t *alp)
     90 {
     91 
     92 	/*
     93 	 * If someone else holds the lock use simple reads until it
     94 	 * is released, then retry the atomic operation. This reduces
     95 	 * memory bus contention because the cache-coherency logic
     96 	 * does not have to broadcast invalidates on the lock while
     97 	 * we spin on it.
     98 	 */
     99 	while (__ldstub(alp) != __SIMPLELOCK_UNLOCKED) {
    100 		while (*alp != __SIMPLELOCK_UNLOCKED)
    101 			/* spin */ ;
    102 	}
    103 }
    104 
    105 static __inline int
    106 __cpu_simple_lock_try(__cpu_simple_lock_t *alp)
    107 {
    108 
    109 	return (__ldstub(alp) == __SIMPLELOCK_UNLOCKED);
    110 }
    111 
    112 static __inline void
    113 __cpu_simple_unlock(__cpu_simple_lock_t *alp)
    114 {
    115 
    116 	*alp = __SIMPLELOCK_UNLOCKED;
    117 }
    118 
    119 #endif /* _MACHINE_LOCK_H */
    120