forked from Minki/linux
6415ce9a92
Here is the PIT fix against the TOD patches that Tim pointed out. Many thanks to Tim for hunting this down. Cc: Tim Mann <mann@vmware.com> Signed-off-by: John Stultz <johnstul@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
119 lines
3.1 KiB
C
119 lines
3.1 KiB
C
/*
|
|
* i8253.c 8253/PIT functions
|
|
*
|
|
*/
|
|
#include <linux/clocksource.h>
|
|
#include <linux/spinlock.h>
|
|
#include <linux/jiffies.h>
|
|
#include <linux/sysdev.h>
|
|
#include <linux/module.h>
|
|
#include <linux/init.h>
|
|
|
|
#include <asm/smp.h>
|
|
#include <asm/delay.h>
|
|
#include <asm/i8253.h>
|
|
#include <asm/io.h>
|
|
|
|
#include "io_ports.h"
|
|
|
|
DEFINE_SPINLOCK(i8253_lock);
|
|
EXPORT_SYMBOL(i8253_lock);
|
|
|
|
void setup_pit_timer(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
spin_lock_irqsave(&i8253_lock, flags);
|
|
outb_p(0x34,PIT_MODE); /* binary, mode 2, LSB/MSB, ch 0 */
|
|
udelay(10);
|
|
outb_p(LATCH & 0xff , PIT_CH0); /* LSB */
|
|
udelay(10);
|
|
outb(LATCH >> 8 , PIT_CH0); /* MSB */
|
|
spin_unlock_irqrestore(&i8253_lock, flags);
|
|
}
|
|
|
|
/*
|
|
* Since the PIT overflows every tick, its not very useful
|
|
* to just read by itself. So use jiffies to emulate a free
|
|
* running counter:
|
|
*/
|
|
static cycle_t pit_read(void)
|
|
{
|
|
unsigned long flags;
|
|
int count;
|
|
u32 jifs;
|
|
static int old_count;
|
|
static u32 old_jifs;
|
|
|
|
spin_lock_irqsave(&i8253_lock, flags);
|
|
/*
|
|
* Although our caller may have the read side of xtime_lock,
|
|
* this is now a seqlock, and we are cheating in this routine
|
|
* by having side effects on state that we cannot undo if
|
|
* there is a collision on the seqlock and our caller has to
|
|
* retry. (Namely, old_jifs and old_count.) So we must treat
|
|
* jiffies as volatile despite the lock. We read jiffies
|
|
* before latching the timer count to guarantee that although
|
|
* the jiffies value might be older than the count (that is,
|
|
* the counter may underflow between the last point where
|
|
* jiffies was incremented and the point where we latch the
|
|
* count), it cannot be newer.
|
|
*/
|
|
jifs = jiffies;
|
|
outb_p(0x00, PIT_MODE); /* latch the count ASAP */
|
|
count = inb_p(PIT_CH0); /* read the latched count */
|
|
count |= inb_p(PIT_CH0) << 8;
|
|
|
|
/* VIA686a test code... reset the latch if count > max + 1 */
|
|
if (count > LATCH) {
|
|
outb_p(0x34, PIT_MODE);
|
|
outb_p(LATCH & 0xff, PIT_CH0);
|
|
outb(LATCH >> 8, PIT_CH0);
|
|
count = LATCH - 1;
|
|
}
|
|
|
|
/*
|
|
* It's possible for count to appear to go the wrong way for a
|
|
* couple of reasons:
|
|
*
|
|
* 1. The timer counter underflows, but we haven't handled the
|
|
* resulting interrupt and incremented jiffies yet.
|
|
* 2. Hardware problem with the timer, not giving us continuous time,
|
|
* the counter does small "jumps" upwards on some Pentium systems,
|
|
* (see c't 95/10 page 335 for Neptun bug.)
|
|
*
|
|
* Previous attempts to handle these cases intelligently were
|
|
* buggy, so we just do the simple thing now.
|
|
*/
|
|
if (count > old_count && jifs == old_jifs) {
|
|
count = old_count;
|
|
}
|
|
old_count = count;
|
|
old_jifs = jifs;
|
|
|
|
spin_unlock_irqrestore(&i8253_lock, flags);
|
|
|
|
count = (LATCH - 1) - count;
|
|
|
|
return (cycle_t)(jifs * LATCH) + count;
|
|
}
|
|
|
|
static struct clocksource clocksource_pit = {
|
|
.name = "pit",
|
|
.rating = 110,
|
|
.read = pit_read,
|
|
.mask = CLOCKSOURCE_MASK(32),
|
|
.mult = 0,
|
|
.shift = 20,
|
|
};
|
|
|
|
static int __init init_pit_clocksource(void)
|
|
{
|
|
if (num_possible_cpus() > 4) /* PIT does not scale! */
|
|
return 0;
|
|
|
|
clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20);
|
|
return clocksource_register(&clocksource_pit);
|
|
}
|
|
module_init(init_pit_clocksource);
|