linux/drivers/clocksource/scx200_hrt.c
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   1/*
   2 * Copyright (C) 2006 Jim Cromie
   3 *
   4 * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz
   5 * high-resolution timer.  The Geode SC-1100 (at least) has a buggy
   6 * time stamp counter (TSC), which loses time unless 'idle=poll' is
   7 * given as a boot-arg. In its absence, the Generic Timekeeping code
   8 * will detect and de-rate the bad TSC, allowing this timer to take
   9 * over timekeeping duties.
  10 *
  11 * Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch)
  12 *
  13 * This program is free software; you can redistribute it and/or
  14 * modify it under the terms of the GNU General Public License as
  15 * published by the Free Software Foundation; either version 2 of the
  16 * License, or (at your option) any later version.
  17 */
  18
  19#include <linux/clocksource.h>
  20#include <linux/init.h>
  21#include <linux/module.h>
  22#include <linux/ioport.h>
  23#include <linux/scx200.h>
  24
  25#define NAME "scx200_hrt"
  26
  27static int mhz27;
  28module_param(mhz27, int, 0);    /* load time only */
  29MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
  30
  31static int ppm;
  32module_param(ppm, int, 0);      /* load time only */
  33MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)");
  34
  35/* HiRes Timer configuration register address */
  36#define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5)
  37
  38/* and config settings */
  39#define HR_TMEN (1 << 0)        /* timer interrupt enable */
  40#define HR_TMCLKSEL (1 << 1)    /* 1|0 counts at 27|1 MHz */
  41#define HR_TM27MPD (1 << 2)     /* 1 turns off input clock (power-down) */
  42
  43/* The base timer frequency, * 27 if selected */
  44#define HRT_FREQ   1000000
  45
  46static cycle_t read_hrt(struct clocksource *cs)
  47{
  48        /* Read the timer value */
  49        return (cycle_t) inl(scx200_cb_base + SCx200_TIMER_OFFSET);
  50}
  51
  52static struct clocksource cs_hrt = {
  53        .name           = "scx200_hrt",
  54        .rating         = 250,
  55        .read           = read_hrt,
  56        .mask           = CLOCKSOURCE_MASK(32),
  57        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
  58        /* mult, shift are set based on mhz27 flag */
  59};
  60
  61static int __init init_hrt_clocksource(void)
  62{
  63        u32 freq;
  64        /* Make sure scx200 has initialized the configuration block */
  65        if (!scx200_cb_present())
  66                return -ENODEV;
  67
  68        /* Reserve the timer's ISA io-region for ourselves */
  69        if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET,
  70                            SCx200_TIMER_SIZE,
  71                            "NatSemi SCx200 High-Resolution Timer")) {
  72                pr_warn("unable to lock timer region\n");
  73                return -ENODEV;
  74        }
  75
  76        /* write timer config */
  77        outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0),
  78             scx200_cb_base + SCx200_TMCNFG_OFFSET);
  79
  80        freq = (HRT_FREQ + ppm);
  81        if (mhz27)
  82                freq *= 27;
  83
  84        pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm);
  85
  86        return clocksource_register_hz(&cs_hrt, freq);
  87}
  88
  89module_init(init_hrt_clocksource);
  90
  91MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
  92MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
  93MODULE_LICENSE("GPL");
  94
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