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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");
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