// SPDX-License-Identifier: GPL-2.0/* calibrate.c: default delay calibration * * Excised from init/main.c *  Copyright (C) 1991, 1992  Linus Torvalds */ #include <linux/delay.h>#include <linux/init.h>#include <linux/jiffies.h>#include <linux/kstrtox.h>#include <linux/percpu.h>#include <linux/printk.h>#include <linux/smp.h>#include <linux/stddef.h> unsigned long lpj_fine;unsigned long preset_lpj; static int __init lpj_setup(char *str){	return kstrtoul(str, 0, &preset_lpj) == 0;} __setup("lpj=", lpj_setup); #ifdef CONFIG_ARCH_HAS_DELAY_TIMER /* This routine uses the delay_read_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 calibrate_delay_direct(void){	unsigned long pre_start, start, post_start;	unsigned long pre_end, end, post_end;	unsigned long start_jiffies;	unsigned long timer_rate_min, timer_rate_max;	unsigned long good_timer_sum = 0;	unsigned long good_timer_count = 0;	unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];	int max = -1; /* index of measured_times with max/min values or not set */	int min = -1;	int i; 	if (!delay_read_timer(&pre_start))		return 0; 	/*	 * A simple loop like	 *	while ( jiffies < start_jiffies+1)	 *		start = delay_read_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;		delay_read_timer(&start);		start_jiffies = jiffies;		while (time_before_eq(jiffies, start_jiffies + 1)) {			pre_start = start;			delay_read_timer(&start);		}		delay_read_timer(&post_start); 		pre_end = 0;		end = post_start;		while (time_before_eq(jiffies, start_jiffies + 1 +					       DELAY_CALIBRATION_TICKS)) {			pre_end = end;			delay_read_timer(&end);		}		delay_read_timer(&post_end); 		timer_rate_max = (post_end - pre_start) /					DELAY_CALIBRATION_TICKS;		timer_rate_min = (pre_end - post_start) /					DELAY_CALIBRATION_TICKS; 		/*		 * If the upper limit and lower limit of the timer_rate is		 * >= 12.5% apart, redo calibration.		 */		if (start >= post_end)			printk(KERN_NOTICE "calibrate_delay_direct() ignoring "					"timer_rate as we had a TSC wrap around"					" start=%lu >=post_end=%lu\n",				start, post_end);		if (start < post_end && pre_start != 0 && pre_end != 0 &&		    (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {			good_timer_count++;			good_timer_sum += timer_rate_max;			measured_times[i] = timer_rate_max;			if (max < 0 || timer_rate_max > measured_times[max])				max = i;			if (min < 0 || timer_rate_max < measured_times[min])				min = i;		} else			measured_times[i] = 0; 	} 	/*	 * Find the maximum & minimum - if they differ too much throw out the	 * one with the largest difference from the mean and try again...	 */	while (good_timer_count > 1) {		unsigned long estimate;		unsigned long maxdiff; 		/* compute the estimate */		estimate = (good_timer_sum/good_timer_count);		maxdiff = estimate >> 3; 		/* if range is within 12% let's take it */		if ((measured_times[max] - measured_times[min]) < maxdiff)			return estimate; 		/* ok - drop the worse value and try again... */		good_timer_sum = 0;		good_timer_count = 0;		if ((measured_times[max] - estimate) <				(estimate - measured_times[min])) {			printk(KERN_NOTICE "calibrate_delay_direct() dropping "					"min bogoMips estimate %d = %lu\n",				min, measured_times[min]);			measured_times[min] = 0;			min = max;		} else {			printk(KERN_NOTICE "calibrate_delay_direct() dropping "					"max bogoMips estimate %d = %lu\n",				max, measured_times[max]);			measured_times[max] = 0;			max = min;		} 		for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {			if (measured_times[i] == 0)				continue;			good_timer_count++;			good_timer_sum += measured_times[i];			if (measured_times[i] < measured_times[min])				min = i;			if (measured_times[i] > measured_times[max])				max = i;		} 	} 	printk(KERN_NOTICE "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 calibrate_delay_direct(void){	return 0;}#endif /* * This is the number of bits of precision for the loops_per_jiffy.  Each * time we refine our estimate after the first takes 1.5/HZ seconds, so try * to start with a good estimate. * For the boot cpu we can skip the delay calibration and assign it a value * calculated based on the timer frequency. * For the rest of the CPUs we cannot assume that the timer frequency is same as * the cpu frequency, hence do the calibration for those. */#define LPS_PREC 8 static unsigned long calibrate_delay_converge(void){	/* First stage - slowly accelerate to find initial bounds */	unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;	int trials = 0, band = 0, trial_in_band = 0; 	lpj = (1<<12); 	/* wait for "start of" clock tick */	ticks = jiffies;	while (ticks == jiffies)		; /* nothing */	/* Go .. */	ticks = jiffies;	do {		if (++trial_in_band == (1<<band)) {			++band;			trial_in_band = 0;		}		__delay(lpj * band);		trials += band;	} while (ticks == jiffies);	/*	 * We overshot, so retreat to a clear underestimate. Then estimate	 * the largest likely undershoot. This defines our chop bounds.	 */	trials -= band;	loopadd_base = lpj * band;	lpj_base = lpj * trials; recalibrate:	lpj = lpj_base;	loopadd = loopadd_base; 	/*	 * Do a binary approximation to get lpj set to	 * equal one clock (up to LPS_PREC bits)	 */	chop_limit = lpj >> LPS_PREC;	while (loopadd > chop_limit) {		lpj += loopadd;		ticks = jiffies;		while (ticks == jiffies)			; /* nothing */		ticks = jiffies;		__delay(lpj);		if (jiffies != ticks)	/* longer than 1 tick */			lpj -= loopadd;		loopadd >>= 1;	}	/*	 * If we incremented every single time possible, presume we've	 * massively underestimated initially, and retry with a higher	 * start, and larger range. (Only seen on x86_64, due to SMIs)	 */	if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {		lpj_base = lpj;		loopadd_base <<= 2;		goto recalibrate;	} 	return lpj;} static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 }; /* * Check if cpu calibration delay is already known. For example, * some processors with multi-core sockets may have all cores * with the same calibration delay. * * Architectures should override this function if a faster calibration * method is available. */unsigned long __attribute__((weak)) calibrate_delay_is_known(void){	return 0;} /* * Indicate the cpu delay calibration is done. This can be used by * architectures to stop accepting delay timer registrations after this point. */ void __attribute__((weak)) calibration_delay_done(void){} void calibrate_delay(void){	unsigned long lpj;	static bool printed;	int this_cpu = smp_processor_id(); 	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {		lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);		if (!printed)			pr_info("Calibrating delay loop (skipped) "				"already calibrated this CPU");	} else if (preset_lpj) {		lpj = preset_lpj;		if (!printed)			pr_info("Calibrating delay loop (skipped) "				"preset value.. ");	} else if ((!printed) && lpj_fine) {		lpj = lpj_fine;		pr_info("Calibrating delay loop (skipped), "			"value calculated using timer frequency.. ");	} else if ((lpj = calibrate_delay_is_known())) {		;	} else if ((lpj = calibrate_delay_direct()) != 0) {		if (!printed)			pr_info("Calibrating delay using timer "				"specific routine.. ");	} else {		if (!printed)			pr_info("Calibrating delay loop... ");		lpj = calibrate_delay_converge();	}	per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;	if (!printed)		pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",			lpj/(500000/HZ),			(lpj/(5000/HZ)) % 100, lpj); 	loops_per_jiffy = lpj;	printed = true; 	calibration_delay_done();}