drivers/clocksource/scx200_hrt.c

   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
  23 static int mhz27;
  24 module_param(mhz27, int, 0);    /* load time only */
  25 MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
  26
  27 static int ppm;
  28 module_param(ppm, int, 0);      /* load time only */
  29 MODULE_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
  42 static u64 read_hrt(struct clocksource *cs)
  43 {
  44         /* Read the timer value */
  45         return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET);
  46 }
  47
  48 static 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
  57 static 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
  85 module_init(init_hrt_clocksource);
  86
  87 MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
  88 MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
  89 MODULE_LICENSE("GPL");