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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 | ||
9 | #define HPET_MASK 0xFFFFFFFF | |
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, | |
26 | .mask = (cycle_t)HPET_MASK, | |
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 | ||
64 | return clocksource_register(&clocksource_hpet); | |
65 | } | |
66 | ||
67 | module_init(init_hpet_clocksource); |