scx200_hrt.c 2.8 KB

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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. #include <linux/clocksource.h>
  19. #include <linux/init.h>
  20. #include <linux/module.h>
  21. #include <linux/ioport.h>
  22. #include <linux/scx200.h>
  23. #define NAME "scx200_hrt"
  24. static int mhz27;
  25. module_param(mhz27, int, 0); /* load time only */
  26. MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
  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. /* HiRes Timer configuration register address */
  31. #define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5)
  32. /* and config settings */
  33. #define HR_TMEN (1 << 0) /* timer interrupt enable */
  34. #define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */
  35. #define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */
  36. /* The base timer frequency, * 27 if selected */
  37. #define HRT_FREQ 1000000
  38. static cycle_t read_hrt(struct clocksource *cs)
  39. {
  40. /* Read the timer value */
  41. return (cycle_t) inl(scx200_cb_base + SCx200_TIMER_OFFSET);
  42. }
  43. static struct clocksource cs_hrt = {
  44. .name = "scx200_hrt",
  45. .rating = 250,
  46. .read = read_hrt,
  47. .mask = CLOCKSOURCE_MASK(32),
  48. .flags = CLOCK_SOURCE_IS_CONTINUOUS,
  49. /* mult, shift are set based on mhz27 flag */
  50. };
  51. static int __init init_hrt_clocksource(void)
  52. {
  53. u32 freq;
  54. /* Make sure scx200 has initialized the configuration block */
  55. if (!scx200_cb_present())
  56. return -ENODEV;
  57. /* Reserve the timer's ISA io-region for ourselves */
  58. if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET,
  59. SCx200_TIMER_SIZE,
  60. "NatSemi SCx200 High-Resolution Timer")) {
  61. pr_warn("unable to lock timer region\n");
  62. return -ENODEV;
  63. }
  64. /* write timer config */
  65. outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0),
  66. scx200_cb_base + SCx200_TMCNFG_OFFSET);
  67. freq = (HRT_FREQ + ppm);
  68. if (mhz27)
  69. freq *= 27;
  70. pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm);
  71. return clocksource_register_hz(&cs_hrt, freq);
  72. }
  73. module_init(init_hrt_clocksource);
  74. MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>");
  75. MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
  76. MODULE_LICENSE("GPL");