mutex.h revision 1.7 
1/*	$NetBSD: mutex.h,v 1.7 2007/03/09 19:21:58 thorpej Exp $	*/
2
3/*-
4 * Copyright (c) 2002, 2007 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Jason R. Thorpe and Andrew Doran.
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 _ARM_MUTEX_H_
40#define	_ARM_MUTEX_H_
41
42/*
43 * The ARM mutex implementation is troublesome, because pre-v6 ARM lacks a
44 * compare-and-swap operation.  However, there aren't any MP pre-v6 ARM
45 * systems to speak of.  We are mostly concerned with atomicity with respect
46 * to interrupts.
47 *
48 * ARMv6, however, does have ldrex/strex, and can thus implement an MP-safe
49 * compare-and-swap.
50 *
51 * So, what we have done is impement simple mutexes using a compare-and-swap.
52 * We support pre-ARMv6 by implementing _lock_cas() as a restartable atomic
53 * sequence that is checked by the IRQ vector.  MP-safe ARMv6 support will
54 * be added later.
55 */
56
57#ifndef __MUTEX_PRIVATE
58
59struct kmutex {
60	uintptr_t	mtx_pad1;
61	uint32_t	mtx_pad2;
62};
63
64#else	/* __MUTEX_PRIVATE */
65
66struct kmutex {
67	union {
68		/* Adaptive mutex */
69		volatile uintptr_t	mtxa_owner;	/* 0-3 */
70
71		/* Spin mutex */
72		struct {
73			volatile uint8_t	mtxs_dummy;
74			ipl_cookie_t		mtxs_ipl;
75			__cpu_simple_lock_t	mtxs_lock;
76			volatile uint8_t	mtxs_unused;
77		} s;
78	} u;
79	volatile uint32_t	mtx_id;			/* 4-7 */
80};
81
82#define	mtx_owner		u.mtxa_owner
83#define	mtx_ipl			u.s.mtxs_ipl
84#define	mtx_lock		u.s.mtxs_lock
85
86#if 0
87#define	__HAVE_MUTEX_STUBS		1
88#define	__HAVE_SPIN_MUTEX_STUBS		1
89#endif
90#define	__HAVE_SIMPLE_MUTEXES		1
91
92/*
93 * MUTEX_RECEIVE: no memory barrier required; we're synchronizing against
94 * interrupts, not multiple processors.
95 */
96#define	MUTEX_RECEIVE(mtx)		/* nothing */
97
98/*
99 * MUTEX_GIVE: no memory barrier required; same reason.
100 */
101#define	MUTEX_GIVE(mtx)			/* nothing */
102
103bool	_lock_cas(volatile uintptr_t *, uintptr_t, uintptr_t);
104
105#define	MUTEX_CAS(p, o, n)		_lock_cas((p), (o), (n))
106
107#endif	/* __MUTEX_PRIVATE */
108
109#endif /* _ARM_MUTEX_H_ */
110