sys/arch/arm/include/mutex.h

   1 /*      $NetBSD: mutex.h,v 1.13 2012/09/25 05:24:00 matt 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.  We are mostly concerned with atomicity with respect
  39  * to interrupts.
  40  *
  41  * ARMv6, however, does have ldrex/strex, and can thus implement an MP-safe
  42  * compare-and-swap.
  43  *
  44  * So, what we have done is impement simple mutexes using a compare-and-swap.
  45  * We support pre-ARMv6 by implementing CAS as a restartable atomic sequence
  46  * that is checked by the IRQ vector.  MP-safe ARMv6 support will be added later.
  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 mtax_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_RECEIVE: no memory barrier required; we're synchronizing against
  89  * interrupts, not multiple processors.
  90  */
  91 #define MUTEX_RECEIVE(mtx)              /* nothing */
  92
  93 /*
  94  * MUTEX_GIVE: no memory barrier required; same reason.
  95  */
  96 #define MUTEX_GIVE(mtx)                 /* nothing */
  97
  98 #define MUTEX_CAS(p, o, n)              \
  99     (atomic_cas_ulong((volatile unsigned long *)(p), (o), (n)) == (o))
 100 #ifdef MULTIPROCESSOR
 101 #define MUTEX_SMT_PAUSE()               __asm __volatile("wfe")
 102 #define MUTEX_SMT_WAKE()                __asm __volatile("sev")
 103 #endif
 104
 105 #endif  /* __MUTEX_PRIVATE */
 106
 107 #endif /* _ARM_MUTEX_H_ */