LXR linux/drivers/clocksource/scx200

   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