scx200_hrt.c
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/*
* Copyright (C) 2006 Jim Cromie
*
* This is a clocksource driver for the Geode SCx200's 1 or 27 MHz
* high-resolution timer. The Geode SC-1100 (at least) has a buggy
* time stamp counter (TSC), which loses time unless 'idle=poll' is
* given as a boot-arg. In its absence, the Generic Timekeeping code
* will detect and de-rate the bad TSC, allowing this timer to take
* over timekeeping duties.
*
* Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*/
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/ioport.h>
#include <linux/scx200.h>
#define NAME "scx200_hrt"
static int mhz27;
module_param(mhz27, int, 0); /* load time only */
MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
static int ppm;
module_param(ppm, int, 0); /* load time only */
MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)");
/* HiRes Timer configuration register address */
#define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5)
/* and config settings */
#define HR_TMEN (1 << 0) /* timer interrupt enable */
#define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */
#define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */
/* The base timer frequency, * 27 if selected */
#define HRT_FREQ 1000000
static cycle_t read_hrt(struct clocksource *cs)
{
/* Read the timer value */
return (cycle_t) inl(scx200_cb_base + SCx200_TIMER_OFFSET);
}
static struct clocksource cs_hrt = {
.name = "scx200_hrt",
.rating = 250,
.read = read_hrt,
.mask = CLOCKSOURCE_MASK(32),
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
/* mult, shift are set based on mhz27 flag */
};
static int __init init_hrt_clocksource(void)
{
u32 freq;
/* Make sure scx200 has initialized the configuration block */
if (!scx200_cb_present())
return -ENODEV;
/* Reserve the timer's ISA io-region for ourselves */
if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET,
SCx200_TIMER_SIZE,
"NatSemi SCx200 High-Resolution Timer")) {
pr_warn("unable to lock timer region\n");
return -ENODEV;
}
/* write timer config */
outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0),
scx200_cb_base + SCx200_TMCNFG_OFFSET);
freq = (HRT_FREQ + ppm);
if (mhz27)
freq *= 27;
pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm);
return clocksource_register_hz(&cs_hrt, freq);
}
module_init(init_hrt_clocksource);
MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
MODULE_LICENSE("GPL");