1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
|
/*
* 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;
u64 jifs;
spin_lock_irqsave(&i8253_lock, flags);
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;
}
spin_unlock_irqrestore(&i8253_lock, flags);
jifs = jiffies_64;
jifs -= INITIAL_JIFFIES;
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(64),
.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);
|
