/* * Copyright (C) 2009 Intel Corporation. * Author: Patrick Ohly <patrick.ohly@intel.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ #include <linux/timecompare.h>#include <linux/module.h>#include <linux/slab.h>#include <linux/math64.h>#include <linux/kernel.h> /* * fixed point arithmetic scale factor for skew * * Usually one would measure skew in ppb (parts per billion, 1e9), but * using a factor of 2 simplifies the math. */#define TIMECOMPARE_SKEW_RESOLUTION (((s64)1)<<30) ktime_t timecompare_transform(struct timecompare *sync,			      u64 source_tstamp){	u64 nsec; 	nsec = source_tstamp + sync->offset;	nsec += (s64)(source_tstamp - sync->last_update) * sync->skew /		TIMECOMPARE_SKEW_RESOLUTION; 	return ns_to_ktime(nsec);}EXPORT_SYMBOL_GPL(timecompare_transform); int timecompare_offset(struct timecompare *sync,		       s64 *offset,		       u64 *source_tstamp){	u64 start_source = 0, end_source = 0;	struct {		s64 offset;		s64 duration_target;	} buffer[10], sample, *samples;	int counter = 0, i;	int used;	int index;	int num_samples = sync->num_samples; 	if (num_samples > ARRAY_SIZE(buffer)) {		samples = kmalloc(sizeof(*samples) * num_samples, GFP_ATOMIC);		if (!samples) {			samples = buffer;			num_samples = ARRAY_SIZE(buffer);		}	} else {		samples = buffer;	} 	/* run until we have enough valid samples, but do not try forever */	i = 0;	counter = 0;	while (1) {		u64 ts;		ktime_t start, end; 		start = sync->target();		ts = timecounter_read(sync->source);		end = sync->target(); 		if (!i)			start_source = ts; 		/* ignore negative durations */		sample.duration_target = ktime_to_ns(ktime_sub(end, start));		if (sample.duration_target >= 0) {			/*			 * assume symetric delay to and from source:			 * average target time corresponds to measured			 * source time			 */			sample.offset =				(ktime_to_ns(end) + ktime_to_ns(start)) / 2 -				ts; 			/* simple insertion sort based on duration */			index = counter - 1;			while (index >= 0) {				if (samples[index].duration_target <				    sample.duration_target)					break;				samples[index + 1] = samples[index];				index--;			}			samples[index + 1] = sample;			counter++;		} 		i++;		if (counter >= num_samples || i >= 100000) {			end_source = ts;			break;		}	} 	*source_tstamp = (end_source + start_source) / 2; 	/* remove outliers by only using 75% of the samples */	used = counter * 3 / 4;	if (!used)		used = counter;	if (used) {		/* calculate average */		s64 off = 0;		for (index = 0; index < used; index++)			off += samples[index].offset;		*offset = div_s64(off, used);	} 	if (samples && samples != buffer)		kfree(samples); 	return used;}EXPORT_SYMBOL_GPL(timecompare_offset); void __timecompare_update(struct timecompare *sync,			  u64 source_tstamp){	s64 offset;	u64 average_time; 	if (!timecompare_offset(sync, &offset, &average_time))		return; 	if (!sync->last_update) {		sync->last_update = average_time;		sync->offset = offset;		sync->skew = 0;	} else {		s64 delta_nsec = average_time - sync->last_update; 		/* avoid division by negative or small deltas */		if (delta_nsec >= 10000) {			s64 delta_offset_nsec = offset - sync->offset;			s64 skew; /* delta_offset_nsec *				     TIMECOMPARE_SKEW_RESOLUTION /				     delta_nsec */			u64 divisor; 			/* div_s64() is limited to 32 bit divisor */			skew = delta_offset_nsec * TIMECOMPARE_SKEW_RESOLUTION;			divisor = delta_nsec;			while (unlikely(divisor >= ((s64)1) << 32)) {				/* divide both by 2; beware, right shift				   of negative value has undefined				   behavior and can only be used for				   the positive divisor */				skew = div_s64(skew, 2);				divisor >>= 1;			}			skew = div_s64(skew, divisor); 			/*			 * Calculate new overall skew as 4/16 the			 * old value and 12/16 the new one. This is			 * a rather arbitrary tradeoff between			 * only using the latest measurement (0/16 and			 * 16/16) and even more weight on past measurements.			 */#define TIMECOMPARE_NEW_SKEW_PER_16 12			sync->skew =				div_s64((16 - TIMECOMPARE_NEW_SKEW_PER_16) *					sync->skew +					TIMECOMPARE_NEW_SKEW_PER_16 * skew,					16);			sync->last_update = average_time;			sync->offset = offset;		}	}}EXPORT_SYMBOL_GPL(__timecompare_update);