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(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	     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_hrt, 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