calibrate.c 4.7 KB

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  1. /* calibrate.c: default delay calibration
  2. *
  3. * Excised from init/main.c
  4. * Copyright (C) 1991, 1992 Linus Torvalds
  5. */
  6. #include <linux/jiffies.h>
  7. #include <linux/delay.h>
  8. #include <linux/init.h>
  9. #include <asm/timex.h>
  10. static unsigned long preset_lpj;
  11. static int __init lpj_setup(char *str)
  12. {
  13. preset_lpj = simple_strtoul(str,NULL,0);
  14. return 1;
  15. }
  16. __setup("lpj=", lpj_setup);
  17. #ifdef ARCH_HAS_READ_CURRENT_TIMER
  18. /* This routine uses the read_current_timer() routine and gets the
  19. * loops per jiffy directly, instead of guessing it using delay().
  20. * Also, this code tries to handle non-maskable asynchronous events
  21. * (like SMIs)
  22. */
  23. #define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
  24. #define MAX_DIRECT_CALIBRATION_RETRIES 5
  25. static unsigned long __devinit calibrate_delay_direct(void)
  26. {
  27. unsigned long pre_start, start, post_start;
  28. unsigned long pre_end, end, post_end;
  29. unsigned long start_jiffies;
  30. unsigned long tsc_rate_min, tsc_rate_max;
  31. unsigned long good_tsc_sum = 0;
  32. unsigned long good_tsc_count = 0;
  33. int i;
  34. if (read_current_timer(&pre_start) < 0 )
  35. return 0;
  36. /*
  37. * A simple loop like
  38. * while ( jiffies < start_jiffies+1)
  39. * start = read_current_timer();
  40. * will not do. As we don't really know whether jiffy switch
  41. * happened first or timer_value was read first. And some asynchronous
  42. * event can happen between these two events introducing errors in lpj.
  43. *
  44. * So, we do
  45. * 1. pre_start <- When we are sure that jiffy switch hasn't happened
  46. * 2. check jiffy switch
  47. * 3. start <- timer value before or after jiffy switch
  48. * 4. post_start <- When we are sure that jiffy switch has happened
  49. *
  50. * Note, we don't know anything about order of 2 and 3.
  51. * Now, by looking at post_start and pre_start difference, we can
  52. * check whether any asynchronous event happened or not
  53. */
  54. for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
  55. pre_start = 0;
  56. read_current_timer(&start);
  57. start_jiffies = jiffies;
  58. while (jiffies <= (start_jiffies + 1)) {
  59. pre_start = start;
  60. read_current_timer(&start);
  61. }
  62. read_current_timer(&post_start);
  63. pre_end = 0;
  64. end = post_start;
  65. while (jiffies <=
  66. (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
  67. pre_end = end;
  68. read_current_timer(&end);
  69. }
  70. read_current_timer(&post_end);
  71. tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
  72. tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
  73. /*
  74. * If the upper limit and lower limit of the tsc_rate is
  75. * >= 12.5% apart, redo calibration.
  76. */
  77. if (pre_start != 0 && pre_end != 0 &&
  78. (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
  79. good_tsc_count++;
  80. good_tsc_sum += tsc_rate_max;
  81. }
  82. }
  83. if (good_tsc_count)
  84. return (good_tsc_sum/good_tsc_count);
  85. printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
  86. "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
  87. return 0;
  88. }
  89. #else
  90. static unsigned long __devinit calibrate_delay_direct(void) {return 0;}
  91. #endif
  92. /*
  93. * This is the number of bits of precision for the loops_per_jiffy. Each
  94. * bit takes on average 1.5/HZ seconds. This (like the original) is a little
  95. * better than 1%
  96. */
  97. #define LPS_PREC 8
  98. void __devinit calibrate_delay(void)
  99. {
  100. unsigned long ticks, loopbit;
  101. int lps_precision = LPS_PREC;
  102. if (preset_lpj) {
  103. loops_per_jiffy = preset_lpj;
  104. printk("Calibrating delay loop (skipped)... "
  105. "%lu.%02lu BogoMIPS preset\n",
  106. loops_per_jiffy/(500000/HZ),
  107. (loops_per_jiffy/(5000/HZ)) % 100);
  108. } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
  109. printk("Calibrating delay using timer specific routine.. ");
  110. printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
  111. loops_per_jiffy/(500000/HZ),
  112. (loops_per_jiffy/(5000/HZ)) % 100,
  113. loops_per_jiffy);
  114. } else {
  115. loops_per_jiffy = (1<<12);
  116. printk(KERN_DEBUG "Calibrating delay loop... ");
  117. while ((loops_per_jiffy <<= 1) != 0) {
  118. /* wait for "start of" clock tick */
  119. ticks = jiffies;
  120. while (ticks == jiffies)
  121. /* nothing */;
  122. /* Go .. */
  123. ticks = jiffies;
  124. __delay(loops_per_jiffy);
  125. ticks = jiffies - ticks;
  126. if (ticks)
  127. break;
  128. }
  129. /*
  130. * Do a binary approximation to get loops_per_jiffy set to
  131. * equal one clock (up to lps_precision bits)
  132. */
  133. loops_per_jiffy >>= 1;
  134. loopbit = loops_per_jiffy;
  135. while (lps_precision-- && (loopbit >>= 1)) {
  136. loops_per_jiffy |= loopbit;
  137. ticks = jiffies;
  138. while (ticks == jiffies)
  139. /* nothing */;
  140. ticks = jiffies;
  141. __delay(loops_per_jiffy);
  142. if (jiffies != ticks) /* longer than 1 tick */
  143. loops_per_jiffy &= ~loopbit;
  144. }
  145. /* Round the value and print it */
  146. printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
  147. loops_per_jiffy/(500000/HZ),
  148. (loops_per_jiffy/(5000/HZ)) % 100,
  149. loops_per_jiffy);
  150. }
  151. }