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 
23 static int mhz27;
24 module_param(mhz27, int, 0);	/* load time only */
25 MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
26 
27 static int ppm;
28 module_param(ppm, int, 0);	/* load time only */
29 MODULE_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 
42 static u64 read_hrt(struct clocksource *cs)
43 {
44 	/* Read the timer value */
45 	return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET);
46 }
47 
48 static 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 
57 static 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 
85 module_init(init_hrt_clocksource);
86 
87 MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
88 MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
89 MODULE_LICENSE("GPL");
90