/* calibrate.c: default delay calibration * * Excised from init/main.c *  Copyright (C) 1991, 1992  Linus Torvalds */ #include <linux/jiffies.h>#include <linux/delay.h>#include <linux/init.h> #include <asm/timex.h> static unsigned long preset_lpj;static int __init lpj_setup(char *str){	preset_lpj = simple_strtoul(str,NULL,0);	return 1;} __setup("lpj=", lpj_setup); #ifdef ARCH_HAS_READ_CURRENT_TIMER /* This routine uses the read_current_timer() routine and gets the * loops per jiffy directly, instead of guessing it using delay(). * Also, this code tries to handle non-maskable asynchronous events * (like SMIs) */#define DELAY_CALIBRATION_TICKS			((HZ < 100) ? 1 : (HZ/100))#define MAX_DIRECT_CALIBRATION_RETRIES		5 static unsigned long __devinit calibrate_delay_direct(void){	unsigned long pre_start, start, post_start;	unsigned long pre_end, end, post_end;	unsigned long start_jiffies;	unsigned long tsc_rate_min, tsc_rate_max;	unsigned long good_tsc_sum = 0;	unsigned long good_tsc_count = 0;	int i; 	if (read_current_timer(&pre_start) < 0 )		return 0; 	/*	 * A simple loop like	 *	while ( jiffies < start_jiffies+1)	 *		start = read_current_timer();	 * will not do. As we don't really know whether jiffy switch	 * happened first or timer_value was read first. And some asynchronous	 * event can happen between these two events introducing errors in lpj.	 *	 * So, we do	 * 1. pre_start <- When we are sure that jiffy switch hasn't happened	 * 2. check jiffy switch	 * 3. start <- timer value before or after jiffy switch	 * 4. post_start <- When we are sure that jiffy switch has happened	 *	 * Note, we don't know anything about order of 2 and 3.	 * Now, by looking at post_start and pre_start difference, we can	 * check whether any asynchronous event happened or not	 */ 	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {		pre_start = 0;		read_current_timer(&start);		start_jiffies = jiffies;		while (jiffies <= (start_jiffies + 1)) {			pre_start = start;			read_current_timer(&start);		}		read_current_timer(&post_start); 		pre_end = 0;		end = post_start;		while (jiffies <=		       (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {			pre_end = end;			read_current_timer(&end);		}		read_current_timer(&post_end); 		tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;		tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS; 		/*	 	 * If the upper limit and lower limit of the tsc_rate is		 * >= 12.5% apart, redo calibration.		 */		if (pre_start != 0 && pre_end != 0 &&		    (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {			good_tsc_count++;			good_tsc_sum += tsc_rate_max;		}	} 	if (good_tsc_count)		return (good_tsc_sum/good_tsc_count); 	printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "	       "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");	return 0;}#elsestatic unsigned long __devinit calibrate_delay_direct(void) {return 0;}#endif /* * This is the number of bits of precision for the loops_per_jiffy.  Each * bit takes on average 1.5/HZ seconds.  This (like the original) is a little * better than 1% */#define LPS_PREC 8 void __devinit calibrate_delay(void){	unsigned long ticks, loopbit;	int lps_precision = LPS_PREC; 	if (preset_lpj) {		loops_per_jiffy = preset_lpj;		printk("Calibrating delay loop (skipped)... "			"%lu.%02lu BogoMIPS preset\n",			loops_per_jiffy/(500000/HZ),			(loops_per_jiffy/(5000/HZ)) % 100);	} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {		printk("Calibrating delay using timer specific routine.. ");		printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",			loops_per_jiffy/(500000/HZ),			(loops_per_jiffy/(5000/HZ)) % 100,			loops_per_jiffy);	} else {		loops_per_jiffy = (1<<12); 		printk(KERN_DEBUG "Calibrating delay loop... ");		while ((loops_per_jiffy <<= 1) != 0) {			/* wait for "start of" clock tick */			ticks = jiffies;			while (ticks == jiffies)				/* nothing */;			/* Go .. */			ticks = jiffies;			__delay(loops_per_jiffy);			ticks = jiffies - ticks;			if (ticks)				break;		} 		/*		 * Do a binary approximation to get loops_per_jiffy set to		 * equal one clock (up to lps_precision bits)		 */		loops_per_jiffy >>= 1;		loopbit = loops_per_jiffy;		while (lps_precision-- && (loopbit >>= 1)) {			loops_per_jiffy |= loopbit;			ticks = jiffies;			while (ticks == jiffies)				/* nothing */;			ticks = jiffies;			__delay(loops_per_jiffy);			if (jiffies != ticks)	/* longer than 1 tick */				loops_per_jiffy &= ~loopbit;		} 		/* Round the value and print it */		printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",			loops_per_jiffy/(500000/HZ),			(loops_per_jiffy/(5000/HZ)) % 100,			loops_per_jiffy);	} }