1/*	$NetBSD: mutex.h,v 1.27.4.1 2023/08/09 17:42:01 martin 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#include <sys/types.h>
36
37#ifdef _KERNEL
38#include <machine/intr.h>
39#endif
40
41/*
42 * The ARM mutex implementation is troublesome, because pre-v6 ARM lacks a
43 * compare-and-swap operation.  However, there aren't any MP pre-v6 ARM
44 * systems to speak of.
45 *
46 * ARMv6 and later, however, does have ldrex/strex, and can thus implement an
47 * MP-safe compare-and-swap.
48 *
49 * So, what we have done is implement simple mutexes using a compare-and-swap.
50 * We support pre-ARMv6 by implementing CAS as a restartable atomic sequence
51 * that is checked by the IRQ vector.
52 *
53 */
54
55struct kmutex {
56	union {
57		/* Adaptive mutex */
58		volatile uintptr_t	mtxa_owner;	/* 0-3 */
59
60#ifdef _KERNEL
61		/* Spin mutex */
62		struct {
63			/*
64			 * Since the low bit of mtxa_owner is used to flag this
65			 * mutex as a spin mutex, we can't use the first byte
66			 * or the last byte to store the ipl or lock values.
67			 */
68			volatile uint8_t	mtxs_dummy;
69			ipl_cookie_t		mtxs_ipl;
70			__cpu_simple_lock_t	mtxs_lock;
71			volatile uint8_t	mtxs_unused;
72		} s;
73#endif
74	} u;
75};
76
77#ifdef __MUTEX_PRIVATE
78
79#define	mtx_owner		u.mtxa_owner
80#define	mtx_ipl			u.s.mtxs_ipl
81#define	mtx_lock		u.s.mtxs_lock
82
83#if 0
84#define	__HAVE_MUTEX_STUBS		1
85#define	__HAVE_SPIN_MUTEX_STUBS		1
86#endif
87#define	__HAVE_SIMPLE_MUTEXES		1
88
89#endif	/* __MUTEX_PRIVATE */
90
91__CTASSERT(sizeof(struct kmutex) == sizeof(uintptr_t));
92
93#endif /* _ARM_MUTEX_H_ */