Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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/sched.h> |
| 8 | #include <linux/delay.h> |
| 9 | #include <linux/init.h> |
| 10 | |
Venkatesh Pallipadi | 8a9e1b0 | 2005-06-23 00:08:13 -0700 | [diff] [blame^] | 11 | #include <asm/timex.h> |
| 12 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | |
Venkatesh Pallipadi | 8a9e1b0 | 2005-06-23 00:08:13 -0700 | [diff] [blame^] | 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 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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); |
Venkatesh Pallipadi | 8a9e1b0 | 2005-06-23 00:08:13 -0700 | [diff] [blame^] | 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); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | } |