drivers/acpi/acpica/utlock.c

   1 // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
   2 /******************************************************************************
   3  *
   4  * Module Name: utlock - Reader/Writer lock interfaces
   5  *
   6  * Copyright (C) 2000 - 2019, Intel Corp.
   7  *
   8  *****************************************************************************/
   9
  10 #include <acpi/acpi.h>
  11 #include "accommon.h"
  12
  13 #define _COMPONENT          ACPI_UTILITIES
  14 ACPI_MODULE_NAME("utlock")
  15
  16 /*******************************************************************************
  17  *
  18  * FUNCTION:    acpi_ut_create_rw_lock
  19  *              acpi_ut_delete_rw_lock
  20  *
  21  * PARAMETERS:  lock                - Pointer to a valid RW lock
  22  *
  23  * RETURN:      Status
  24  *
  25  * DESCRIPTION: Reader/writer lock creation and deletion interfaces.
  26  *
  27  ******************************************************************************/
  28 acpi_status acpi_ut_create_rw_lock(struct acpi_rw_lock *lock)
  29 {
  30         acpi_status status;
  31
  32         lock->num_readers = 0;
  33         status = acpi_os_create_mutex(&lock->reader_mutex);
  34         if (ACPI_FAILURE(status)) {
  35                 return (status);
  36         }
  37
  38         status = acpi_os_create_mutex(&lock->writer_mutex);
  39         return (status);
  40 }
  41
  42 void acpi_ut_delete_rw_lock(struct acpi_rw_lock *lock)
  43 {
  44
  45         acpi_os_delete_mutex(lock->reader_mutex);
  46         acpi_os_delete_mutex(lock->writer_mutex);
  47
  48         lock->num_readers = 0;
  49         lock->reader_mutex = NULL;
  50         lock->writer_mutex = NULL;
  51 }
  52
  53 /*******************************************************************************
  54  *
  55  * FUNCTION:    acpi_ut_acquire_read_lock
  56  *              acpi_ut_release_read_lock
  57  *
  58  * PARAMETERS:  lock                - Pointer to a valid RW lock
  59  *
  60  * RETURN:      Status
  61  *
  62  * DESCRIPTION: Reader interfaces for reader/writer locks. On acquisition,
  63  *              only the first reader acquires the write mutex. On release,
  64  *              only the last reader releases the write mutex. Although this
  65  *              algorithm can in theory starve writers, this should not be a
  66  *              problem with ACPICA since the subsystem is infrequently used
  67  *              in comparison to (for example) an I/O system.
  68  *
  69  ******************************************************************************/
  70
  71 acpi_status acpi_ut_acquire_read_lock(struct acpi_rw_lock *lock)
  72 {
  73         acpi_status status;
  74
  75         status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
  76         if (ACPI_FAILURE(status)) {
  77                 return (status);
  78         }
  79
  80         /* Acquire the write lock only for the first reader */
  81
  82         lock->num_readers++;
  83         if (lock->num_readers == 1) {
  84                 status =
  85                     acpi_os_acquire_mutex(lock->writer_mutex,
  86                                           ACPI_WAIT_FOREVER);
  87         }
  88
  89         acpi_os_release_mutex(lock->reader_mutex);
  90         return (status);
  91 }
  92
  93 acpi_status acpi_ut_release_read_lock(struct acpi_rw_lock *lock)
  94 {
  95         acpi_status status;
  96
  97         status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
  98         if (ACPI_FAILURE(status)) {
  99                 return (status);
 100         }
 101
 102         /* Release the write lock only for the very last reader */
 103
 104         lock->num_readers--;
 105         if (lock->num_readers == 0) {
 106                 acpi_os_release_mutex(lock->writer_mutex);
 107         }
 108
 109         acpi_os_release_mutex(lock->reader_mutex);
 110         return (status);
 111 }
 112
 113 /*******************************************************************************
 114  *
 115  * FUNCTION:    acpi_ut_acquire_write_lock
 116  *              acpi_ut_release_write_lock
 117  *
 118  * PARAMETERS:  lock                - Pointer to a valid RW lock
 119  *
 120  * RETURN:      Status
 121  *
 122  * DESCRIPTION: Writer interfaces for reader/writer locks. Simply acquire or
 123  *              release the writer mutex associated with the lock. Acquisition
 124  *              of the lock is fully exclusive and will block all readers and
 125  *              writers until it is released.
 126  *
 127  ******************************************************************************/
 128
 129 acpi_status acpi_ut_acquire_write_lock(struct acpi_rw_lock *lock)
 130 {
 131         acpi_status status;
 132
 133         status = acpi_os_acquire_mutex(lock->writer_mutex, ACPI_WAIT_FOREVER);
 134         return (status);
 135 }
 136
 137 void acpi_ut_release_write_lock(struct acpi_rw_lock *lock)
 138 {
 139
 140         acpi_os_release_mutex(lock->writer_mutex);
 141 }