+++ /dev/null
-/*
- * Utility code which helps transforming between two different time
- * bases, called "source" and "target" time in this code.
- *
- * Source time has to be provided via the timecounter API while target
- * time is accessed via a function callback whose prototype
- * intentionally matches ktime_get() and ktime_get_real(). These
- * interfaces where chosen like this so that the code serves its
- * initial purpose without additional glue code.
- *
- * This purpose is synchronizing a hardware clock in a NIC with system
- * time, in order to implement the Precision Time Protocol (PTP,
- * IEEE1588) with more accurate hardware assisted time stamping. In
- * that context only synchronization against system time (=
- * ktime_get_real()) is currently needed. But this utility code might
- * become useful in other situations, which is why it was written as
- * general purpose utility code.
- *
- * The source timecounter is assumed to return monotonically
- * increasing time (but this code does its best to compensate if that
- * is not the case) whereas target time may jump.
- *
- * The target time corresponding to a source time is determined by
- * reading target time, reading source time, reading target time
- * again, then assuming that average target time corresponds to source
- * time. In other words, the assumption is that reading the source
- * time is slow and involves equal time for sending the request and
- * receiving the reply, whereas reading target time is assumed to be
- * fast.
- *
- * 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 and conditions of the GNU General Public License,
- * version 2, as published by the Free Software Foundation.
- *
- * This program is distributed in the hope 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.,
- * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
- */
-#ifndef _LINUX_TIMECOMPARE_H
-#define _LINUX_TIMECOMPARE_H
-
-#include <linux/clocksource.h>
-#include <linux/ktime.h>
-
-/**
- * struct timecompare - stores state and configuration for the two clocks
- *
- * Initialize to zero, then set source/target/num_samples.
- *
- * Transformation between source time and target time is done with:
- * target_time = source_time + offset +
- * (source_time - last_update) * skew /
- * TIMECOMPARE_SKEW_RESOLUTION
- *
- * @source: used to get source time stamps via timecounter_read()
- * @target: function returning target time (for example, ktime_get
- * for monotonic time, or ktime_get_real for wall clock)
- * @num_samples: number of times that source time and target time are to
- * be compared when determining their offset
- * @offset: (target time - source time) at the time of the last update
- * @skew: average (target time - source time) / delta source time *
- * TIMECOMPARE_SKEW_RESOLUTION
- * @last_update: last source time stamp when time offset was measured
- */
-struct timecompare {
- struct timecounter *source;
- ktime_t (*target)(void);
- int num_samples;
-
- s64 offset;
- s64 skew;
- u64 last_update;
-};
-
-/**
- * timecompare_transform - transform source time stamp into target time base
- * @sync: context for time sync
- * @source_tstamp: the result of timecounter_read() or
- * timecounter_cyc2time()
- */
-extern ktime_t timecompare_transform(struct timecompare *sync,
- u64 source_tstamp);
-
-/**
- * timecompare_offset - measure current (target time - source time) offset
- * @sync: context for time sync
- * @offset: average offset during sample period returned here
- * @source_tstamp: average source time during sample period returned here
- *
- * Returns number of samples used. Might be zero (= no result) in the
- * unlikely case that target time was monotonically decreasing for all
- * samples (= broken).
- */
-extern int timecompare_offset(struct timecompare *sync,
- s64 *offset,
- u64 *source_tstamp);
-
-extern void __timecompare_update(struct timecompare *sync,
- u64 source_tstamp);
-
-/**
- * timecompare_update - update offset and skew by measuring current offset
- * @sync: context for time sync
- * @source_tstamp: the result of timecounter_read() or
- * timecounter_cyc2time(), pass zero to force update
- *
- * Updates are only done at most once per second.
- */
-static inline void timecompare_update(struct timecompare *sync,
- u64 source_tstamp)
-{
- if (!source_tstamp ||
- (s64)(source_tstamp - sync->last_update) >= NSEC_PER_SEC)
- __timecompare_update(sync, source_tstamp);
-}
-
-#endif /* _LINUX_TIMECOMPARE_H */
+++ /dev/null
-/*
- * 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);
projects / cascardo / linux.git / commitdiff