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5d0cf410 JS |
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 | ||
7f9f303a | 9 | #define HPET_MASK CLOCKSOURCE_MASK(32) |
5d0cf410 JS |
10 | #define HPET_SHIFT 22 |
11 | ||
12 | /* FSEC = 10^-15 NSEC = 10^-9 */ | |
13 | #define FSEC_PER_NSEC 1000000 | |
14 | ||
5b71bddb | 15 | static void __iomem *hpet_ptr; |
5d0cf410 JS |
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, | |
7f9f303a | 26 | .mask = HPET_MASK, |
5d0cf410 JS |
27 | .mult = 0, /* set below */ |
28 | .shift = HPET_SHIFT, | |
73b08d2a | 29 | .flags = CLOCK_SOURCE_IS_CONTINUOUS, |
5d0cf410 JS |
30 | }; |
31 | ||
32 | static int __init init_hpet_clocksource(void) | |
33 | { | |
34 | unsigned long hpet_period; | |
35 | void __iomem* hpet_base; | |
36 | u64 tmp; | |
fa5cecd1 | 37 | int err; |
5d0cf410 | 38 | |
30f3174d | 39 | if (!is_hpet_enabled()) |
5d0cf410 JS |
40 | return -ENODEV; |
41 | ||
42 | /* calculate the hpet address: */ | |
5b71bddb | 43 | hpet_base = ioremap_nocache(hpet_address, HPET_MMAP_SIZE); |
5d0cf410 JS |
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 | ||
fa5cecd1 AL |
64 | err = clocksource_register(&clocksource_hpet); |
65 | if (err) | |
66 | iounmap(hpet_base); | |
67 | ||
68 | return err; | |
5d0cf410 JS |
69 | } |
70 | ||
71 | module_init(init_hpet_clocksource); |