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 55 struct 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_ */ 94