1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (C) 2006 Jim Cromie
4 *
5 * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz
6 * high-resolution timer. The Geode SC-1100 (at least) has a buggy
7 * time stamp counter (TSC), which loses time unless 'idle=poll' is
8 * given as a boot-arg. In its absence, the Generic Timekeeping code
9 * will detect and de-rate the bad TSC, allowing this timer to take
10 * over timekeeping duties.
11 *
12 * Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch)
13 */
14
15#include <linux/clocksource.h>
16#include <linux/init.h>
17#include <linux/module.h>
18#include <linux/ioport.h>
19#include <linux/scx200.h>
20
21#define NAME "scx200_hrt"
22
23static int mhz27;
24module_param(mhz27, int, 0); /* load time only */
25MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
26
27static int ppm;
28module_param(ppm, int, 0); /* load time only */
29MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)");
30
31/* HiRes Timer configuration register address */
32#define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5)
33
34/* and config settings */
35#define HR_TMEN (1 << 0) /* timer interrupt enable */
36#define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */
37#define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */
38
39/* The base timer frequency, * 27 if selected */
40#define HRT_FREQ 1000000
41
42static u64 read_hrt(struct clocksource *cs)
43{
44 /* Read the timer value */
45 return (u64) inl(port: scx200_cb_base + SCx200_TIMER_OFFSET);
46}
47
48static struct clocksource cs_hrt = {
49 .name = "scx200_hrt",
50 .rating = 250,
51 .read = read_hrt,
52 .mask = CLOCKSOURCE_MASK(32),
53 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
54 /* mult, shift are set based on mhz27 flag */
55};
56
57static int __init init_hrt_clocksource(void)
58{
59 u32 freq;
60 /* Make sure scx200 has initialized the configuration block */
61 if (!scx200_cb_present())
62 return -ENODEV;
63
64 /* Reserve the timer's ISA io-region for ourselves */
65 if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET,
66 SCx200_TIMER_SIZE,
67 "NatSemi SCx200 High-Resolution Timer")) {
68 pr_warn("unable to lock timer region\n");
69 return -ENODEV;
70 }
71
72 /* write timer config */
73 outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0),
74 port: scx200_cb_base + SCx200_TMCNFG_OFFSET);
75
76 freq = (HRT_FREQ + ppm);
77 if (mhz27)
78 freq *= 27;
79
80 pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm);
81
82 return clocksource_register_hz(cs: &cs_hrt, hz: freq);
83}
84
85module_init(init_hrt_clocksource);
86
87MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
88MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
89MODULE_LICENSE("GPL");
90

source code of linux/drivers/clocksource/scx200_hrt.c