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80 lines
1.8 KiB
80 lines
1.8 KiB
20 years ago
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/* calibrate.c: default delay calibration
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*
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* Excised from init/main.c
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* Copyright (C) 1991, 1992 Linus Torvalds
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*/
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#include <linux/sched.h>
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#include <linux/delay.h>
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#include <linux/init.h>
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static unsigned long preset_lpj;
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static int __init lpj_setup(char *str)
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{
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preset_lpj = simple_strtoul(str,NULL,0);
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return 1;
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}
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__setup("lpj=", lpj_setup);
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/*
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* This is the number of bits of precision for the loops_per_jiffy. Each
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* bit takes on average 1.5/HZ seconds. This (like the original) is a little
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* better than 1%
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*/
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#define LPS_PREC 8
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void __devinit calibrate_delay(void)
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{
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unsigned long ticks, loopbit;
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int lps_precision = LPS_PREC;
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if (preset_lpj) {
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loops_per_jiffy = preset_lpj;
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printk("Calibrating delay loop (skipped)... "
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"%lu.%02lu BogoMIPS preset\n",
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loops_per_jiffy/(500000/HZ),
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(loops_per_jiffy/(5000/HZ)) % 100);
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} else {
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loops_per_jiffy = (1<<12);
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printk(KERN_DEBUG "Calibrating delay loop... ");
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while ((loops_per_jiffy <<= 1) != 0) {
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/* wait for "start of" clock tick */
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ticks = jiffies;
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while (ticks == jiffies)
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/* nothing */;
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/* Go .. */
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ticks = jiffies;
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__delay(loops_per_jiffy);
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ticks = jiffies - ticks;
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if (ticks)
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break;
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}
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/*
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* Do a binary approximation to get loops_per_jiffy set to
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* equal one clock (up to lps_precision bits)
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*/
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loops_per_jiffy >>= 1;
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loopbit = loops_per_jiffy;
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while (lps_precision-- && (loopbit >>= 1)) {
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loops_per_jiffy |= loopbit;
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ticks = jiffies;
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while (ticks == jiffies)
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/* nothing */;
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ticks = jiffies;
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__delay(loops_per_jiffy);
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if (jiffies != ticks) /* longer than 1 tick */
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loops_per_jiffy &= ~loopbit;
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}
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/* Round the value and print it */
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printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
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loops_per_jiffy/(500000/HZ),
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(loops_per_jiffy/(5000/HZ)) % 100,
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loops_per_jiffy);
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}
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}
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