sys/arch/arm/include/mutex.h

   1 /*      $NetBSD: mutex.h,v 1.20 2015/02/25 13:52:42 joerg 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
  49 #ifndef __MUTEX_PRIVATE
  50
  51 struct kmutex {
  52         uintptr_t       mtx_pad1;
  53 };
  54
  55 #else   /* __MUTEX_PRIVATE */
  56
  57 struct kmutex {
  58         union {
  59                 /* Adaptive mutex */
  60                 volatile uintptr_t      mtxa_owner;     /* 0-3 */
  61
  62                 /* Spin mutex */
  63                 struct {
  64                         /*
  65                          * Since the low bit of mtxa_owner is used to flag this
  66                          * mutex as a spin mutex, we can't use the first byte
  67                          * or the last byte to store the ipl or lock values.
  68                          */
  69                         volatile uint8_t        mtxs_dummy;
  70                         ipl_cookie_t            mtxs_ipl;
  71                         __cpu_simple_lock_t     mtxs_lock;
  72                         volatile uint8_t        mtxs_unused;
  73                 } s;
  74         } u;
  75 };
  76
  77 #define mtx_owner               u.mtxa_owner
  78 #define mtx_ipl                 u.s.mtxs_ipl
  79 #define mtx_lock                u.s.mtxs_lock
  80
  81 #if 0
  82 #define __HAVE_MUTEX_STUBS              1
  83 #define __HAVE_SPIN_MUTEX_STUBS         1
  84 #endif
  85 #define __HAVE_SIMPLE_MUTEXES           1
  86
  87 /*
  88  * MUTEX_{GIVE,RECEIVE}: no memory barrier is required in the UP case;
  89  * we're synchronizing against interrupts, not multiple processors.
  90  */
  91 #ifdef MULTIPROCESSOR
  92 #ifdef _ARM_ARCH_7
  93 #define MUTEX_RECEIVE(mtx)              __asm __volatile("dmb" ::: "memory")
  94 #else
  95 #define MUTEX_RECEIVE(mtx)              membar_consumer()
  96 #endif
  97 #else
  98 #define MUTEX_RECEIVE(mtx)              /* nothing */
  99 #endif
 100
 101 #ifdef MULTIPROCESSOR
 102 #ifdef _ARM_ARCH_7
 103 #define MUTEX_GIVE(mtx)                 __asm __volatile("dsb" ::: "memory")
 104 #else
 105 #define MUTEX_GIVE(mtx)                 membar_producer()
 106 #endif
 107 #else
 108 #define MUTEX_GIVE(mtx)                 /* nothing */
 109 #endif
 110
 111 #define MUTEX_CAS(p, o, n)              \
 112     (atomic_cas_ulong((volatile unsigned long *)(p), (o), (n)) == (o))
 113 #ifdef MULTIPROCESSOR
 114 #define MUTEX_SMT_PAUSE()               __asm __volatile("wfe")
 115 #define MUTEX_SMT_WAKE()                __asm __volatile("sev")
 116 #endif
 117
 118 #endif  /* __MUTEX_PRIVATE */
 119
 120 #endif /* _ARM_MUTEX_H_ */