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1 | /* |
2 | * i8253.c 8253/PIT functions |
3 | * |
4 | */ |
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5 | #include <linux/clocksource.h> |
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6 | #include <linux/spinlock.h> |
7 | #include <linux/jiffies.h> |
8 | #include <linux/sysdev.h> |
9 | #include <linux/module.h> |
10 | #include <linux/init.h> |
11 | |
12 | #include <asm/smp.h> |
13 | #include <asm/delay.h> |
14 | #include <asm/i8253.h> |
15 | #include <asm/io.h> |
16 | |
17 | #include "io_ports.h" |
18 | |
19 | DEFINE_SPINLOCK(i8253_lock); |
20 | EXPORT_SYMBOL(i8253_lock); |
21 | |
22 | void setup_pit_timer(void) |
23 | { |
24 | unsigned long flags; |
25 | |
26 | spin_lock_irqsave(&i8253_lock, flags); |
27 | outb_p(0x34,PIT_MODE); /* binary, mode 2, LSB/MSB, ch 0 */ |
28 | udelay(10); |
29 | outb_p(LATCH & 0xff , PIT_CH0); /* LSB */ |
30 | udelay(10); |
31 | outb(LATCH >> 8 , PIT_CH0); /* MSB */ |
32 | spin_unlock_irqrestore(&i8253_lock, flags); |
33 | } |
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34 | |
35 | /* |
36 | * Since the PIT overflows every tick, its not very useful |
37 | * to just read by itself. So use jiffies to emulate a free |
38 | * running counter: |
39 | */ |
40 | static cycle_t pit_read(void) |
41 | { |
42 | unsigned long flags; |
43 | int count; |
44 | u64 jifs; |
45 | |
46 | spin_lock_irqsave(&i8253_lock, flags); |
47 | outb_p(0x00, PIT_MODE); /* latch the count ASAP */ |
48 | count = inb_p(PIT_CH0); /* read the latched count */ |
49 | count |= inb_p(PIT_CH0) << 8; |
50 | |
51 | /* VIA686a test code... reset the latch if count > max + 1 */ |
52 | if (count > LATCH) { |
53 | outb_p(0x34, PIT_MODE); |
54 | outb_p(LATCH & 0xff, PIT_CH0); |
55 | outb(LATCH >> 8, PIT_CH0); |
56 | count = LATCH - 1; |
57 | } |
58 | spin_unlock_irqrestore(&i8253_lock, flags); |
59 | |
60 | jifs = jiffies_64; |
61 | |
62 | jifs -= INITIAL_JIFFIES; |
63 | count = (LATCH-1) - count; |
64 | |
65 | return (cycle_t)(jifs * LATCH) + count; |
66 | } |
67 | |
68 | static struct clocksource clocksource_pit = { |
69 | .name = "pit", |
70 | .rating = 110, |
71 | .read = pit_read, |
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72 | .mask = CLOCKSOURCE_MASK(64), |
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73 | .mult = 0, |
74 | .shift = 20, |
75 | }; |
76 | |
77 | static int __init init_pit_clocksource(void) |
78 | { |
79 | if (num_possible_cpus() > 4) /* PIT does not scale! */ |
80 | return 0; |
81 | |
82 | clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20); |
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83 | return clocksource_register(&clocksource_pit); |
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84 | } |
85 | module_init(init_pit_clocksource); |