mutex.h revision 1.24 
1/*	$NetBSD: mutex.h,v 1.24 2020/12/01 14:52:36 skrll 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/*
36 * The ARM mutex implementation is troublesome, because pre-v6 ARM lacks a
37 * compare-and-swap operation.  However, there aren't any MP pre-v6 ARM
38 * systems to speak of.
39 *
40 * ARMv6 and later, however, does have ldrex/strex, and can thus implement an
41 * MP-safe compare-and-swap.
42 *
43 * So, what we have done is implement simple mutexes using a compare-and-swap.
44 * We support pre-ARMv6 by implementing CAS as a restartable atomic sequence
45 * that is checked by the IRQ vector.
46 *
47 */
48
49struct kmutex {
50	union {
51		/* Adaptive mutex */
52		volatile uintptr_t	mtxa_owner;	/* 0-3 */
53
54#ifdef _KERNEL
55		/* Spin mutex */
56		struct {
57			/*
58			 * Since the low bit of mtxa_owner is used to flag this
59			 * mutex as a spin mutex, we can't use the first byte
60			 * or the last byte to store the ipl or lock values.
61			 */
62			volatile uint8_t	mtxs_dummy;
63			ipl_cookie_t		mtxs_ipl;
64			__cpu_simple_lock_t	mtxs_lock;
65			volatile uint8_t	mtxs_unused;
66		} s;
67#endif
68	} u;
69};
70
71#ifdef __MUTEX_PRIVATE
72
73#define	mtx_owner		u.mtxa_owner
74#define	mtx_ipl			u.s.mtxs_ipl
75#define	mtx_lock		u.s.mtxs_lock
76
77#if 0
78#define	__HAVE_MUTEX_STUBS		1
79#define	__HAVE_SPIN_MUTEX_STUBS		1
80#endif
81#define	__HAVE_SIMPLE_MUTEXES		1
82
83#define	MUTEX_CAS(p, o, n)		\
84    (atomic_cas_ulong((volatile unsigned long *)(p), (o), (n)) == (o))
85#ifdef MULTIPROCESSOR
86#define	MUTEX_SMT_PAUSE()		__asm __volatile("wfe")
87#define	MUTEX_SMT_WAKE()		__asm __volatile("sev")
88#endif
89
90#endif	/* __MUTEX_PRIVATE */
91
92#endif /* _ARM_MUTEX_H_ */
93