73b08d2aa4
Using a flag filed allows to encode more than one information into a variable. Preparatory patch for the generic clocksource verification. [mingo@elte.hu: convert vmitime.c to the new clocksource flag] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Cc: john stultz <johnstul@us.ibm.com> Cc: Roman Zippel <zippel@linux-m68k.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
73 lines
2.5 KiB
C
73 lines
2.5 KiB
C
/***********************************************************************
|
|
* 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/init.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 reccomended
|
|
* 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 then 8 overflow 32bits when
|
|
* HZ=100.
|
|
*/
|
|
#define JIFFIES_SHIFT 8
|
|
|
|
static cycle_t jiffies_read(void)
|
|
{
|
|
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,
|
|
};
|
|
|
|
static int __init init_jiffies_clocksource(void)
|
|
{
|
|
return clocksource_register(&clocksource_jiffies);
|
|
}
|
|
|
|
module_init(init_jiffies_clocksource);
|