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1 | #include <linux/clocksource.h> |
2 | #include <linux/errno.h> |
3 | #include <linux/hpet.h> |
4 | #include <linux/init.h> |
5 | |
6 | #include <asm/hpet.h> |
7 | #include <asm/io.h> |
8 | |
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9 | #define HPET_MASK CLOCKSOURCE_MASK(32) |
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10 | #define HPET_SHIFT 22 |
11 | |
12 | /* FSEC = 10^-15 NSEC = 10^-9 */ |
13 | #define FSEC_PER_NSEC 1000000 |
14 | |
15 | static void *hpet_ptr; |
16 | |
17 | static cycle_t read_hpet(void) |
18 | { |
19 | return (cycle_t)readl(hpet_ptr); |
20 | } |
21 | |
22 | static struct clocksource clocksource_hpet = { |
23 | .name = "hpet", |
24 | .rating = 250, |
25 | .read = read_hpet, |
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26 | .mask = HPET_MASK, |
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27 | .mult = 0, /* set below */ |
28 | .shift = HPET_SHIFT, |
29 | .is_continuous = 1, |
30 | }; |
31 | |
32 | static int __init init_hpet_clocksource(void) |
33 | { |
34 | unsigned long hpet_period; |
35 | void __iomem* hpet_base; |
36 | u64 tmp; |
37 | |
38 | if (!hpet_address) |
39 | return -ENODEV; |
40 | |
41 | /* calculate the hpet address: */ |
42 | hpet_base = |
43 | (void __iomem*)ioremap_nocache(hpet_address, HPET_MMAP_SIZE); |
44 | hpet_ptr = hpet_base + HPET_COUNTER; |
45 | |
46 | /* calculate the frequency: */ |
47 | hpet_period = readl(hpet_base + HPET_PERIOD); |
48 | |
49 | /* |
50 | * hpet period is in femto seconds per cycle |
51 | * so we need to convert this to ns/cyc units |
52 | * aproximated by mult/2^shift |
53 | * |
54 | * fsec/cyc * 1nsec/1000000fsec = nsec/cyc = mult/2^shift |
55 | * fsec/cyc * 1ns/1000000fsec * 2^shift = mult |
56 | * fsec/cyc * 2^shift * 1nsec/1000000fsec = mult |
57 | * (fsec/cyc << shift)/1000000 = mult |
58 | * (hpet_period << shift)/FSEC_PER_NSEC = mult |
59 | */ |
60 | tmp = (u64)hpet_period << HPET_SHIFT; |
61 | do_div(tmp, FSEC_PER_NSEC); |
62 | clocksource_hpet.mult = (u32)tmp; |
63 | |
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64 | return clocksource_register(&clocksource_hpet); |
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65 | } |
66 | |
67 | module_init(init_hpet_clocksource); |