1 /* calibrate.c: default delay calibration 2 * 3 * Excised from init/main.c 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 */ 6 7 #include <linux/jiffies.h> 8 #include <linux/delay.h> 9 #include <linux/init.h> 10 11 #include <asm/timex.h> 12 13 static unsigned long preset_lpj; 14 static int __init lpj_setup(char *str) 15 { 16 preset_lpj = simple_strtoul(str,NULL,0); 17 return 1; 18 } 19 20 __setup("lpj=", lpj_setup); 21 22 #ifdef ARCH_HAS_READ_CURRENT_TIMER 23 24 /* This routine uses the read_current_timer() routine and gets the 25 * loops per jiffy directly, instead of guessing it using delay(). 26 * Also, this code tries to handle non-maskable asynchronous events 27 * (like SMIs) 28 */ 29 #define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100)) 30 #define MAX_DIRECT_CALIBRATION_RETRIES 5 31 32 static unsigned long __devinit calibrate_delay_direct(void) 33 { 34 unsigned long pre_start, start, post_start; 35 unsigned long pre_end, end, post_end; 36 unsigned long start_jiffies; 37 unsigned long tsc_rate_min, tsc_rate_max; 38 unsigned long good_tsc_sum = 0; 39 unsigned long good_tsc_count = 0; 40 int i; 41 42 if (read_current_timer(&pre_start) < 0 ) 43 return 0; 44 45 /* 46 * A simple loop like 47 * while ( jiffies < start_jiffies+1) 48 * start = read_current_timer(); 49 * will not do. As we don't really know whether jiffy switch 50 * happened first or timer_value was read first. And some asynchronous 51 * event can happen between these two events introducing errors in lpj. 52 * 53 * So, we do 54 * 1. pre_start <- When we are sure that jiffy switch hasn't happened 55 * 2. check jiffy switch 56 * 3. start <- timer value before or after jiffy switch 57 * 4. post_start <- When we are sure that jiffy switch has happened 58 * 59 * Note, we don't know anything about order of 2 and 3. 60 * Now, by looking at post_start and pre_start difference, we can 61 * check whether any asynchronous event happened or not 62 */ 63 64 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) { 65 pre_start = 0; 66 read_current_timer(&start); 67 start_jiffies = jiffies; 68 while (jiffies <= (start_jiffies + 1)) { 69 pre_start = start; 70 read_current_timer(&start); 71 } 72 read_current_timer(&post_start); 73 74 pre_end = 0; 75 end = post_start; 76 while (jiffies <= 77 (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) { 78 pre_end = end; 79 read_current_timer(&end); 80 } 81 read_current_timer(&post_end); 82 83 tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS; 84 tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS; 85 86 /* 87 * If the upper limit and lower limit of the tsc_rate is 88 * >= 12.5% apart, redo calibration. 89 */ 90 if (pre_start != 0 && pre_end != 0 && 91 (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) { 92 good_tsc_count++; 93 good_tsc_sum += tsc_rate_max; 94 } 95 } 96 97 if (good_tsc_count) 98 return (good_tsc_sum/good_tsc_count); 99 100 printk(KERN_WARNING "calibrate_delay_direct() failed to get a good " 101 "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n"); 102 return 0; 103 } 104 #else 105 static unsigned long __devinit calibrate_delay_direct(void) {return 0;} 106 #endif 107 108 /* 109 * This is the number of bits of precision for the loops_per_jiffy. Each 110 * bit takes on average 1.5/HZ seconds. This (like the original) is a little 111 * better than 1% 112 */ 113 #define LPS_PREC 8 114 115 void __devinit calibrate_delay(void) 116 { 117 unsigned long ticks, loopbit; 118 int lps_precision = LPS_PREC; 119 120 if (preset_lpj) { 121 loops_per_jiffy = preset_lpj; 122 printk("Calibrating delay loop (skipped)... " 123 "%lu.%02lu BogoMIPS preset\n", 124 loops_per_jiffy/(500000/HZ), 125 (loops_per_jiffy/(5000/HZ)) % 100); 126 } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) { 127 printk("Calibrating delay using timer specific routine.. "); 128 printk("%lu.%02lu BogoMIPS (lpj=%lu)\n", 129 loops_per_jiffy/(500000/HZ), 130 (loops_per_jiffy/(5000/HZ)) % 100, 131 loops_per_jiffy); 132 } else { 133 loops_per_jiffy = (1<<12); 134 135 printk(KERN_DEBUG "Calibrating delay loop... "); 136 while ((loops_per_jiffy <<= 1) != 0) { 137 /* wait for "start of" clock tick */ 138 ticks = jiffies; 139 while (ticks == jiffies) 140 /* nothing */; 141 /* Go .. */ 142 ticks = jiffies; 143 __delay(loops_per_jiffy); 144 ticks = jiffies - ticks; 145 if (ticks) 146 break; 147 } 148 149 /* 150 * Do a binary approximation to get loops_per_jiffy set to 151 * equal one clock (up to lps_precision bits) 152 */ 153 loops_per_jiffy >>= 1; 154 loopbit = loops_per_jiffy; 155 while (lps_precision-- && (loopbit >>= 1)) { 156 loops_per_jiffy |= loopbit; 157 ticks = jiffies; 158 while (ticks == jiffies) 159 /* nothing */; 160 ticks = jiffies; 161 __delay(loops_per_jiffy); 162 if (jiffies != ticks) /* longer than 1 tick */ 163 loops_per_jiffy &= ~loopbit; 164 } 165 166 /* Round the value and print it */ 167 printk("%lu.%02lu BogoMIPS (lpj=%lu)\n", 168 loops_per_jiffy/(500000/HZ), 169 (loops_per_jiffy/(5000/HZ)) % 100, 170 loops_per_jiffy); 171 } 172 173 } 174