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6ae7440e JC |
1 | /* |
2 | * Copyright (C) 2006 Jim Cromie | |
3 | * | |
4 | * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz | |
5 | * high-resolution timer. The Geode SC-1100 (at least) has a buggy | |
6 | * time stamp counter (TSC), which loses time unless 'idle=poll' is | |
7 | * given as a boot-arg. In its absence, the Generic Timekeeping code | |
8 | * will detect and de-rate the bad TSC, allowing this timer to take | |
9 | * over timekeeping duties. | |
10 | * | |
11 | * Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch) | |
12 | * | |
13 | * This program is free software; you can redistribute it and/or | |
14 | * modify it under the terms of the GNU General Public License as | |
15 | * published by the Free Software Foundation; either version 2 of the | |
16 | * License, or (at your option) any later version. | |
17 | */ | |
18 | ||
19 | #include <linux/clocksource.h> | |
20 | #include <linux/init.h> | |
21 | #include <linux/module.h> | |
22 | #include <linux/ioport.h> | |
23 | #include <linux/scx200.h> | |
24 | ||
25 | #define NAME "scx200_hrt" | |
26 | ||
27 | static int mhz27; | |
28 | module_param(mhz27, int, 0); /* load time only */ | |
29 | MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)"); | |
30 | ||
31 | static int ppm; | |
32 | module_param(ppm, int, 0); /* load time only */ | |
33 | MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)"); | |
34 | ||
35 | /* HiRes Timer configuration register address */ | |
36 | #define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5) | |
37 | ||
38 | /* and config settings */ | |
39 | #define HR_TMEN (1 << 0) /* timer interrupt enable */ | |
40 | #define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */ | |
41 | #define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */ | |
42 | ||
43 | /* The base timer frequency, * 27 if selected */ | |
44 | #define HRT_FREQ 1000000 | |
45 | ||
8e19608e | 46 | static cycle_t read_hrt(struct clocksource *cs) |
6ae7440e JC |
47 | { |
48 | /* Read the timer value */ | |
49 | return (cycle_t) inl(scx200_cb_base + SCx200_TIMER_OFFSET); | |
50 | } | |
51 | ||
6ae7440e JC |
52 | static struct clocksource cs_hrt = { |
53 | .name = "scx200_hrt", | |
54 | .rating = 250, | |
55 | .read = read_hrt, | |
56 | .mask = CLOCKSOURCE_MASK(32), | |
73b08d2a | 57 | .flags = CLOCK_SOURCE_IS_CONTINUOUS, |
6ae7440e JC |
58 | /* mult, shift are set based on mhz27 flag */ |
59 | }; | |
60 | ||
61 | static int __init init_hrt_clocksource(void) | |
62 | { | |
12d6d412 | 63 | u32 freq; |
856fe98f | 64 | /* Make sure scx200 has initialized the configuration block */ |
6ae7440e JC |
65 | if (!scx200_cb_present()) |
66 | return -ENODEV; | |
67 | ||
68 | /* Reserve the timer's ISA io-region for ourselves */ | |
69 | if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET, | |
70 | SCx200_TIMER_SIZE, | |
71 | "NatSemi SCx200 High-Resolution Timer")) { | |
d976f762 | 72 | pr_warn("unable to lock timer region\n"); |
6ae7440e JC |
73 | return -ENODEV; |
74 | } | |
75 | ||
76 | /* write timer config */ | |
856fe98f | 77 | outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0), |
6ae7440e JC |
78 | scx200_cb_base + SCx200_TMCNFG_OFFSET); |
79 | ||
12d6d412 JS |
80 | freq = (HRT_FREQ + ppm); |
81 | if (mhz27) | |
82 | freq *= 27; | |
83 | ||
10ea9d6f | 84 | pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm); |
6ae7440e | 85 | |
12d6d412 | 86 | return clocksource_register_hz(&cs_hrt, freq); |
6ae7440e JC |
87 | } |
88 | ||
89 | module_init(init_hrt_clocksource); | |
90 | ||
91 | MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>"); | |
92 | MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); | |
93 | MODULE_LICENSE("GPL"); |