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
read_hrt(struct clocksource * cs)46 static u64 read_hrt(struct clocksource *cs)
47 {
48 /* Read the timer value */
49 return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET);
50 }
51
52 static struct clocksource cs_hrt = {
53 .name = "scx200_hrt",
54 .rating = 250,
55 .read = read_hrt,
56 .mask = CLOCKSOURCE_MASK(32),
57 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
58 /* mult, shift are set based on mhz27 flag */
59 };
60
init_hrt_clocksource(void)61 static int __init init_hrt_clocksource(void)
62 {
63 u32 freq;
64 /* Make sure scx200 has initialized the configuration block */
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")) {
72 pr_warn("unable to lock timer region\n");
73 return -ENODEV;
74 }
75
76 /* write timer config */
77 outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0),
78 scx200_cb_base + SCx200_TMCNFG_OFFSET);
79
80 freq = (HRT_FREQ + ppm);
81 if (mhz27)
82 freq *= 27;
83
84 pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm);
85
86 return clocksource_register_hz(&cs_hrt, freq);
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");
94
