/******************************************************************************
   *
   * Module Name: utlock - Reader/Writer lock interfaces
   *
   *****************************************************************************/
  
  /*
   * Copyright (C) 2000 - 2013, Intel Corp.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions, and the following disclaimer,
   *    without modification.
   * 2. Redistributions in binary form must reproduce at minimum a disclaimer
   *    substantially similar to the "NO WARRANTY" disclaimer below
   *    ("Disclaimer") and any redistribution must be conditioned upon
   *    including a substantially similar Disclaimer requirement for further
   *    binary redistribution.
   * 3. Neither the names of the above-listed copyright holders nor the names
   *    of any contributors may be used to endorse or promote products derived
   *    from this software without specific prior written permission.
   *
   * Alternatively, this software may be distributed under the terms of the
   * GNU General Public License ("GPL") version 2 as published by the Free
   * Software Foundation.
   *
   * NO WARRANTY
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
   * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGES.
   */
  
  #include <acpi/acpi.h>
  #include "accommon.h"
  
  #define _COMPONENT          ACPI_UTILITIES
  ACPI_MODULE_NAME("utlock")
  
  /*******************************************************************************
   *
   * FUNCTION:    acpi_ut_create_rw_lock
   *              acpi_ut_delete_rw_lock
   *
   * PARAMETERS:  lock                - Pointer to a valid RW lock
   *
   * RETURN:      Status
   *
   * DESCRIPTION: Reader/writer lock creation and deletion interfaces.
   *
   ******************************************************************************/
  acpi_status acpi_ut_create_rw_lock(struct acpi_rw_lock *lock)
  {
  	acpi_status status;
  
  	lock->num_readers = 0;
  	status = acpi_os_create_mutex(&lock->reader_mutex);
  	if (ACPI_FAILURE(status)) {
  		return (status);
  	}
  
  	status = acpi_os_create_mutex(&lock->writer_mutex);
  	return (status);
  }
  
  void acpi_ut_delete_rw_lock(struct acpi_rw_lock *lock)
  {
  
  	acpi_os_delete_mutex(lock->reader_mutex);
  	acpi_os_delete_mutex(lock->writer_mutex);
  
  	lock->num_readers = 0;
  	lock->reader_mutex = NULL;
  	lock->writer_mutex = NULL;
  }
  
  /*******************************************************************************
   *
   * FUNCTION:    acpi_ut_acquire_read_lock
   *              acpi_ut_release_read_lock
   *
   * PARAMETERS:  lock                - Pointer to a valid RW lock
   *
   * RETURN:      Status
   *
   * DESCRIPTION: Reader interfaces for reader/writer locks. On acquisition,
   *              only the first reader acquires the write mutex. On release,
   *              only the last reader releases the write mutex. Although this
   *              algorithm can in theory starve writers, this should not be a
   *              problem with ACPICA since the subsystem is infrequently used
   *              in comparison to (for example) an I/O system.
   *
   ******************************************************************************/
  
  acpi_status acpi_ut_acquire_read_lock(struct acpi_rw_lock *lock)
  {
  	acpi_status status;
  
  	status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
  	if (ACPI_FAILURE(status)) {
  		return (status);
  	}
  
  	/* Acquire the write lock only for the first reader */
  
  	lock->num_readers++;
  	if (lock->num_readers == 1) {
  		status =
  		    acpi_os_acquire_mutex(lock->writer_mutex,
  					  ACPI_WAIT_FOREVER);
  	}
  
  	acpi_os_release_mutex(lock->reader_mutex);
  	return (status);
  }
  
  acpi_status acpi_ut_release_read_lock(struct acpi_rw_lock *lock)
  {
  	acpi_status status;
  
  	status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
  	if (ACPI_FAILURE(status)) {
  		return (status);
  	}
  
  	/* Release the write lock only for the very last reader */
  
  	lock->num_readers--;
  	if (lock->num_readers == 0) {
  		acpi_os_release_mutex(lock->writer_mutex);
  	}
  
  	acpi_os_release_mutex(lock->reader_mutex);
  	return (status);
  }
  
  /*******************************************************************************
   *
   * FUNCTION:    acpi_ut_acquire_write_lock
   *              acpi_ut_release_write_lock
   *
   * PARAMETERS:  lock                - Pointer to a valid RW lock
   *
   * RETURN:      Status
   *
   * DESCRIPTION: Writer interfaces for reader/writer locks. Simply acquire or
   *              release the writer mutex associated with the lock. Acquisition
   *              of the lock is fully exclusive and will block all readers and
   *              writers until it is released.
   *
   ******************************************************************************/
  
  acpi_status acpi_ut_acquire_write_lock(struct acpi_rw_lock *lock)
  {
  	acpi_status status;
  
  	status = acpi_os_acquire_mutex(lock->writer_mutex, ACPI_WAIT_FOREVER);
  	return (status);
  }
  
  void acpi_ut_release_write_lock(struct acpi_rw_lock *lock)
  {
  
  	acpi_os_release_mutex(lock->writer_mutex);
  }