drivers/clocksource/scx200_hrt.c

   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
  27 static int mhz27;
  28 module_param(mhz27, int, 0);    /* load time only */
  29 MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
  30
  31 static int ppm;
  32 module_param(ppm, int, 0);      /* load time only */
  33 MODULE_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
  46 static 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
  52 static 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
  61 static 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
  89 module_init(init_hrt_clocksource);
  90
  91 MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
  92 MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
  93 MODULE_LICENSE("GPL");