init/calibrate.c - kernel/msm-4.9 - Gitiles

 /* 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 <linux/timex.h>
 #include <linux/smp.h>
 #include <linux/percpu.h>

 unsigned long lpj_fine;
 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 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 (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 (time_before_eq(jiffies, start_jiffies + 1)) {
 			pre_start = start;
 			read_current_timer(&start);
 		}
 		read_current_timer(&post_start);

 		pre_end = 0;
 		end = post_start;
 		while (time_before_eq(jiffies, start_jiffies + 1 +
 					       DELAY_CALIBRATION_TICKS)) {
 			pre_end = end;
 			read_current_timer(&end);
 		}
 		read_current_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;
 }
 #else
 static 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;
 }

 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;
 }
	/* 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 <linux/timex.h>
	#include <linux/smp.h>
	#include <linux/percpu.h>

	unsigned long lpj_fine;
	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 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 (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 (time_before_eq(jiffies, start_jiffies + 1)) {
	pre_start = start;
	read_current_timer(&start);
	}
	read_current_timer(&post_start);

	pre_end = 0;
	end = post_start;
	while (time_before_eq(jiffies, start_jiffies + 1 +
	DELAY_CALIBRATION_TICKS)) {
	pre_end = end;
	read_current_timer(&end);
	}
	read_current_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;
	}
	#else
	static 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;
	}

	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;
	}