/***********************************************************************
  * linux/kernel/time/jiffies.c
  *
  * This file contains the jiffies based clocksource.
  *
  * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  *
  ************************************************************************/
  #include <linux/clocksource.h>
  #include <linux/jiffies.h>

  #include <linux/module.h>

  #include <linux/init.h>

  #include "tick-internal.h"

  /* The Jiffies based clocksource is the lowest common
   * denominator clock source which should function on
   * all systems. It has the same coarse resolution as
   * the timer interrupt frequency HZ and it suffers
   * inaccuracies caused by missed or lost timer
   * interrupts and the inability for the timer
   * interrupt hardware to accuratly tick at the

   * requested HZ value. It is also not recommended

   * for "tick-less" systems.
   */
  #define NSEC_PER_JIFFY	((u32)((((u64)NSEC_PER_SEC)<<8)/ACTHZ))
  
  /* Since jiffies uses a simple NSEC_PER_JIFFY multiplier
   * conversion, the .shift value could be zero. However
   * this would make NTP adjustments impossible as they are
   * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
   * shift both the nominator and denominator the same
   * amount, and give ntp adjustments in units of 1/2^8
   *
   * The value 8 is somewhat carefully chosen, as anything
   * larger can result in overflows. NSEC_PER_JIFFY grows as

   * HZ shrinks, so values greater than 8 overflow 32bits when

   * HZ=100.
   */
  #define JIFFIES_SHIFT	8

  static cycle_t jiffies_read(struct clocksource *cs)

  {
  	return (cycle_t) jiffies;
  }
  
  struct clocksource clocksource_jiffies = {
  	.name		= "jiffies",

  	.rating		= 1, /* lowest valid rating*/

  	.read		= jiffies_read,
  	.mask		= 0xffffffff, /*32bits*/
  	.mult		= NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
  	.shift		= JIFFIES_SHIFT,

  };

  #if (BITS_PER_LONG < 64)
  u64 get_jiffies_64(void)
  {
  	unsigned long seq;
  	u64 ret;
  
  	do {
  		seq = read_seqbegin(&xtime_lock);
  		ret = jiffies_64;
  	} while (read_seqretry(&xtime_lock, seq));
  	return ret;
  }
  EXPORT_SYMBOL(get_jiffies_64);
  #endif
  
  EXPORT_SYMBOL(jiffies);

  static int __init init_jiffies_clocksource(void)
  {

  	return clocksource_register(&clocksource_jiffies);

  }

  core_initcall(init_jiffies_clocksource);

  
  struct clocksource * __init __weak clocksource_default_clock(void)
  {
  	return &clocksource_jiffies;
  }