mutex.h revision 1.28 
1/*	$NetBSD: mutex.h,v 1.28 2023/07/11 10:41:58 riastradh 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 *
19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29 * POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#ifndef _ARM_MUTEX_H_
33#define	_ARM_MUTEX_H_
34
35#ifdef _KERNEL
36#include <machine/intr.h>
37#include <machine/lock.h>
38#endif
39
40/*
41 * The ARM mutex implementation is troublesome, because pre-v6 ARM lacks a
42 * compare-and-swap operation.  However, there aren't any MP pre-v6 ARM
43 * systems to speak of.
44 *
45 * ARMv6 and later, however, does have ldrex/strex, and can thus implement an
46 * MP-safe compare-and-swap.
47 *
48 * So, what we have done is implement simple mutexes using a compare-and-swap.
49 * We support pre-ARMv6 by implementing CAS as a restartable atomic sequence
50 * that is checked by the IRQ vector.
51 *
52 */
53
54struct kmutex {
55	union {
56		/* Adaptive mutex */
57		volatile uintptr_t	mtxa_owner;	/* 0-3 */
58
59#ifdef _KERNEL
60		/* Spin mutex */
61		struct {
62			/*
63			 * Since the low bit of mtxa_owner is used to flag this
64			 * mutex as a spin mutex, we can't use the first byte
65			 * or the last byte to store the ipl or lock values.
66			 */
67			volatile uint8_t	mtxs_dummy;
68			ipl_cookie_t		mtxs_ipl;
69			__cpu_simple_lock_t	mtxs_lock;
70			volatile uint8_t	mtxs_unused;
71		} s;
72#endif
73	} u;
74};
75
76#ifdef __MUTEX_PRIVATE
77
78#define	mtx_owner		u.mtxa_owner
79#define	mtx_ipl			u.s.mtxs_ipl
80#define	mtx_lock		u.s.mtxs_lock
81
82#if 0
83#define	__HAVE_MUTEX_STUBS		1
84#define	__HAVE_SPIN_MUTEX_STUBS		1
85#endif
86#define	__HAVE_SIMPLE_MUTEXES		1
87
88#endif	/* __MUTEX_PRIVATE */
89
90__CTASSERT(sizeof(struct kmutex) == sizeof(uintptr_t));
91
92#endif /* _ARM_MUTEX_H_ */
93