delay.c 2.4 KB

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  1. // SPDX-License-Identifier: GPL-2.0-only
  2. /*
  3. * Delay loops based on the OpenRISC implementation.
  4. *
  5. * Copyright (C) 2012 ARM Limited
  6. *
  7. * Author: Will Deacon <will.deacon@arm.com>
  8. */
  9. #include <linux/clocksource.h>
  10. #include <linux/delay.h>
  11. #include <linux/init.h>
  12. #include <linux/kernel.h>
  13. #include <linux/module.h>
  14. #include <linux/timex.h>
  15. /*
  16. * Default to the loop-based delay implementation.
  17. */
  18. struct arm_delay_ops arm_delay_ops __ro_after_init = {
  19. .delay = __loop_delay,
  20. .const_udelay = __loop_const_udelay,
  21. .udelay = __loop_udelay,
  22. };
  23. static const struct delay_timer *delay_timer;
  24. static bool delay_calibrated;
  25. static u64 delay_res;
  26. int read_current_timer(unsigned long *timer_val)
  27. {
  28. if (!delay_timer)
  29. return -ENXIO;
  30. *timer_val = delay_timer->read_current_timer();
  31. return 0;
  32. }
  33. EXPORT_SYMBOL_GPL(read_current_timer);
  34. static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
  35. {
  36. return (cyc * mult) >> shift;
  37. }
  38. static void __timer_delay(unsigned long cycles)
  39. {
  40. cycles_t start = get_cycles();
  41. while ((get_cycles() - start) < cycles)
  42. cpu_relax();
  43. }
  44. static void __timer_const_udelay(unsigned long xloops)
  45. {
  46. unsigned long long loops = xloops;
  47. loops *= arm_delay_ops.ticks_per_jiffy;
  48. __timer_delay(loops >> UDELAY_SHIFT);
  49. }
  50. static void __timer_udelay(unsigned long usecs)
  51. {
  52. __timer_const_udelay(usecs * UDELAY_MULT);
  53. }
  54. void __init register_current_timer_delay(const struct delay_timer *timer)
  55. {
  56. u32 new_mult, new_shift;
  57. u64 res;
  58. clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
  59. NSEC_PER_SEC, 3600);
  60. res = cyc_to_ns(1ULL, new_mult, new_shift);
  61. if (res > 1000) {
  62. pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
  63. timer, res);
  64. return;
  65. }
  66. if (!delay_calibrated && (!delay_res || (res < delay_res))) {
  67. pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
  68. delay_timer = timer;
  69. lpj_fine = timer->freq / HZ;
  70. delay_res = res;
  71. /* cpufreq may scale loops_per_jiffy, so keep a private copy */
  72. arm_delay_ops.ticks_per_jiffy = lpj_fine;
  73. arm_delay_ops.delay = __timer_delay;
  74. arm_delay_ops.const_udelay = __timer_const_udelay;
  75. arm_delay_ops.udelay = __timer_udelay;
  76. } else {
  77. pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
  78. }
  79. }
  80. unsigned long calibrate_delay_is_known(void)
  81. {
  82. delay_calibrated = true;
  83. return lpj_fine;
  84. }
  85. void calibration_delay_done(void)
  86. {
  87. delay_calibrated = true;
  88. }