1/* $NetBSD: mutex.h,v 1.29 2023/07/12 12:50:12 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#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_ */