drivers/acpi/acpica/utlock.c

   1 /******************************************************************************
   2  *
   3  * Module Name: utlock - Reader/Writer lock interfaces
   4  *
   5  *****************************************************************************/
   6
   7 /*
   8  * Copyright (C) 2000 - 2009, Intel Corp.
   9  * All rights reserved.
  10  *
  11  * Redistribution and use in source and binary forms, with or without
  12  * modification, are permitted provided that the following conditions
  13  * are met:
  14  * 1. Redistributions of source code must retain the above copyright
  15  *    notice, this list of conditions, and the following disclaimer,
  16  *    without modification.
  17  * 2. Redistributions in binary form must reproduce at minimum a disclaimer
  18  *    substantially similar to the "NO WARRANTY" disclaimer below
  19  *    ("Disclaimer") and any redistribution must be conditioned upon
  20  *    including a substantially similar Disclaimer requirement for further
  21  *    binary redistribution.
  22  * 3. Neither the names of the above-listed copyright holders nor the names
  23  *    of any contributors may be used to endorse or promote products derived
  24  *    from this software without specific prior written permission.
  25  *
  26  * Alternatively, this software may be distributed under the terms of the
  27  * GNU General Public License ("GPL") version 2 as published by the Free
  28  * Software Foundation.
  29  *
  30  * NO WARRANTY
  31  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  32  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  33  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
  34  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  35  * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  36  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  37  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  38  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  39  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  40  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  41  * POSSIBILITY OF SUCH DAMAGES.
  42  */
  43
  44 #include <acpi/acpi.h>
  45 #include "accommon.h"
  46
  47 #define _COMPONENT          ACPI_UTILITIES
  48 ACPI_MODULE_NAME("utlock")
  49
  50 /*******************************************************************************
  51  *
  52  * FUNCTION:    acpi_ut_create_rw_lock
  53  *              acpi_ut_delete_rw_lock
  54  *
  55  * PARAMETERS:  Lock                - Pointer to a valid RW lock
  56  *
  57  * RETURN:      Status
  58  *
  59  * DESCRIPTION: Reader/writer lock creation and deletion interfaces.
  60  *
  61  ******************************************************************************/
  62 acpi_status acpi_ut_create_rw_lock(struct acpi_rw_lock *lock)
  63 {
  64         acpi_status status;
  65
  66         lock->num_readers = 0;
  67         status = acpi_os_create_mutex(&lock->reader_mutex);
  68         if (ACPI_FAILURE(status)) {
  69                 return status;
  70         }
  71
  72         status = acpi_os_create_mutex(&lock->writer_mutex);
  73         return status;
  74 }
  75
  76 void acpi_ut_delete_rw_lock(struct acpi_rw_lock *lock)
  77 {
  78
  79         acpi_os_delete_mutex(lock->reader_mutex);
  80         acpi_os_delete_mutex(lock->writer_mutex);
  81
  82         lock->num_readers = 0;
  83         lock->reader_mutex = NULL;
  84         lock->writer_mutex = NULL;
  85 }
  86
  87 /*******************************************************************************
  88  *
  89  * FUNCTION:    acpi_ut_acquire_read_lock
  90  *              acpi_ut_release_read_lock
  91  *
  92  * PARAMETERS:  Lock                - Pointer to a valid RW lock
  93  *
  94  * RETURN:      Status
  95  *
  96  * DESCRIPTION: Reader interfaces for reader/writer locks. On acquisition,
  97  *              only the first reader acquires the write mutex. On release,
  98  *              only the last reader releases the write mutex. Although this
  99  *              algorithm can in theory starve writers, this should not be a
 100  *              problem with ACPICA since the subsystem is infrequently used
 101  *              in comparison to (for example) an I/O system.
 102  *
 103  ******************************************************************************/
 104
 105 acpi_status acpi_ut_acquire_read_lock(struct acpi_rw_lock *lock)
 106 {
 107         acpi_status status;
 108
 109         status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
 110         if (ACPI_FAILURE(status)) {
 111                 return status;
 112         }
 113
 114         /* Acquire the write lock only for the first reader */
 115
 116         lock->num_readers++;
 117         if (lock->num_readers == 1) {
 118                 status =
 119                     acpi_os_acquire_mutex(lock->writer_mutex,
 120                                           ACPI_WAIT_FOREVER);
 121         }
 122
 123         acpi_os_release_mutex(lock->reader_mutex);
 124         return status;
 125 }
 126
 127 acpi_status acpi_ut_release_read_lock(struct acpi_rw_lock *lock)
 128 {
 129         acpi_status status;
 130
 131         status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
 132         if (ACPI_FAILURE(status)) {
 133                 return status;
 134         }
 135
 136         /* Release the write lock only for the very last reader */
 137
 138         lock->num_readers--;
 139         if (lock->num_readers == 0) {
 140                 acpi_os_release_mutex(lock->writer_mutex);
 141         }
 142
 143         acpi_os_release_mutex(lock->reader_mutex);
 144         return status;
 145 }
 146
 147 /*******************************************************************************
 148  *
 149  * FUNCTION:    acpi_ut_acquire_write_lock
 150  *              acpi_ut_release_write_lock
 151  *
 152  * PARAMETERS:  Lock                - Pointer to a valid RW lock
 153  *
 154  * RETURN:      Status
 155  *
 156  * DESCRIPTION: Writer interfaces for reader/writer locks. Simply acquire or
 157  *              release the writer mutex associated with the lock. Acquisition
 158  *              of the lock is fully exclusive and will block all readers and
 159  *              writers until it is released.
 160  *
 161  ******************************************************************************/
 162
 163 acpi_status acpi_ut_acquire_write_lock(struct acpi_rw_lock *lock)
 164 {
 165         acpi_status status;
 166
 167         status = acpi_os_acquire_mutex(lock->writer_mutex, ACPI_WAIT_FOREVER);
 168         return status;
 169 }
 170
 171 void acpi_ut_release_write_lock(struct acpi_rw_lock *lock)
 172 {
 173
 174         acpi_os_release_mutex(lock->writer_mutex);
 175 }