xref: /openbmc/linux/drivers/iio/common/inv_sensors/inv_sensors_timestamp.c (revision 6ee0c842)

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2020 Invensense, Inc.
 */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/math64.h>
#include <linux/module.h>

#include <linux/iio/common/inv_sensors_timestamp.h>

/* compute jitter, min and max following jitter in per mille */
#define INV_SENSORS_TIMESTAMP_JITTER(_val, _jitter)		\
	(div_s64((_val) * (_jitter), 1000))
#define INV_SENSORS_TIMESTAMP_MIN(_val, _jitter)		\
	(((_val) * (1000 - (_jitter))) / 1000)
#define INV_SENSORS_TIMESTAMP_MAX(_val, _jitter)		\
	(((_val) * (1000 + (_jitter))) / 1000)

/* Add a new value inside an accumulator and update the estimate value */
static void inv_update_acc(struct inv_sensors_timestamp_acc *acc, uint32_t val)
{
	uint64_t sum = 0;
	size_t i;

	acc->values[acc->idx++] = val;
	if (acc->idx >= ARRAY_SIZE(acc->values))
		acc->idx = 0;

	/* compute the mean of all stored values, use 0 as empty slot */
	for (i = 0; i < ARRAY_SIZE(acc->values); ++i) {
		if (acc->values[i] == 0)
			break;
		sum += acc->values[i];
	}

	acc->val = div_u64(sum, i);
}

void inv_sensors_timestamp_init(struct inv_sensors_timestamp *ts,
				const struct inv_sensors_timestamp_chip *chip)
{
	memset(ts, 0, sizeof(*ts));

	/* save chip parameters and compute min and max clock period */
	ts->chip = *chip;
	ts->min_period = INV_SENSORS_TIMESTAMP_MIN(chip->clock_period, chip->jitter);
	ts->max_period = INV_SENSORS_TIMESTAMP_MAX(chip->clock_period, chip->jitter);

	/* current multiplier and period values after reset */
	ts->mult = chip->init_period / chip->clock_period;
	ts->period = chip->init_period;

	/* use theoretical value for chip period */
	inv_update_acc(&ts->chip_period, chip->clock_period);
}
EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_init, IIO_INV_SENSORS_TIMESTAMP);

int inv_sensors_timestamp_update_odr(struct inv_sensors_timestamp *ts,
				     uint32_t period, bool fifo)
{
	uint32_t mult;

	/* when FIFO is on, prevent odr change if one is already pending */
	if (fifo && ts->new_mult != 0)
		return -EAGAIN;

	mult = period / ts->chip.clock_period;
	if (mult != ts->mult)
		ts->new_mult = mult;

	return 0;
}
EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_update_odr, IIO_INV_SENSORS_TIMESTAMP);

static bool inv_validate_period(struct inv_sensors_timestamp *ts, uint32_t period, uint32_t mult)
{
	uint32_t period_min, period_max;

	/* check that period is acceptable */
	period_min = ts->min_period * mult;
	period_max = ts->max_period * mult;
	if (period > period_min && period < period_max)
		return true;
	else
		return false;
}

static bool inv_update_chip_period(struct inv_sensors_timestamp *ts,
				    uint32_t mult, uint32_t period)
{
	uint32_t new_chip_period;

	if (!inv_validate_period(ts, period, mult))
		return false;

	/* update chip internal period estimation */
	new_chip_period = period / mult;
	inv_update_acc(&ts->chip_period, new_chip_period);
	ts->period = ts->mult * ts->chip_period.val;

	return true;
}

static void inv_align_timestamp_it(struct inv_sensors_timestamp *ts)
{
	const int64_t period_min = ts->min_period * ts->mult;
	const int64_t period_max = ts->max_period * ts->mult;
	int64_t add_max, sub_max;
	int64_t delta, jitter;
	int64_t adjust;

	/* delta time between last sample and last interrupt */
	delta = ts->it.lo - ts->timestamp;

	/* adjust timestamp while respecting jitter */
	add_max = period_max - (int64_t)ts->period;
	sub_max = period_min - (int64_t)ts->period;
	jitter = INV_SENSORS_TIMESTAMP_JITTER((int64_t)ts->period, ts->chip.jitter);
	if (delta > jitter)
		adjust = add_max;
	else if (delta < -jitter)
		adjust = sub_max;
	else
		adjust = 0;

	ts->timestamp += adjust;
}

void inv_sensors_timestamp_interrupt(struct inv_sensors_timestamp *ts,
				      uint32_t fifo_period, size_t fifo_nb,
				      size_t sensor_nb, int64_t timestamp)
{
	struct inv_sensors_timestamp_interval *it;
	int64_t delta, interval;
	const uint32_t fifo_mult = fifo_period / ts->chip.clock_period;
	uint32_t period = ts->period;
	bool valid = false;

	if (fifo_nb == 0)
		return;

	/* update interrupt timestamp and compute chip and sensor periods */
	it = &ts->it;
	it->lo = it->up;
	it->up = timestamp;
	delta = it->up - it->lo;
	if (it->lo != 0) {
		/* compute period: delta time divided by number of samples */
		period = div_s64(delta, fifo_nb);
		valid = inv_update_chip_period(ts, fifo_mult, period);
	}

	/* no previous data, compute theoritical value from interrupt */
	if (ts->timestamp == 0) {
		/* elapsed time: sensor period * sensor samples number */
		interval = (int64_t)ts->period * (int64_t)sensor_nb;
		ts->timestamp = it->up - interval;
		return;
	}

	/* if interrupt interval is valid, sync with interrupt timestamp */
	if (valid)
		inv_align_timestamp_it(ts);
}
EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_interrupt, IIO_INV_SENSORS_TIMESTAMP);

void inv_sensors_timestamp_apply_odr(struct inv_sensors_timestamp *ts,
				     uint32_t fifo_period, size_t fifo_nb,
				     unsigned int fifo_no)
{
	int64_t interval;
	uint32_t fifo_mult;

	if (ts->new_mult == 0)
		return;

	/* update to new multiplier and update period */
	ts->mult = ts->new_mult;
	ts->new_mult = 0;
	ts->period = ts->mult * ts->chip_period.val;

	/*
	 * After ODR change the time interval with the previous sample is
	 * undertermined (depends when the change occures). So we compute the
	 * timestamp from the current interrupt using the new FIFO period, the
	 * total number of samples and the current sample numero.
	 */
	if (ts->timestamp != 0) {
		/* compute measured fifo period */
		fifo_mult = fifo_period / ts->chip.clock_period;
		fifo_period = fifo_mult * ts->chip_period.val;
		/* computes time interval between interrupt and this sample */
		interval = (int64_t)(fifo_nb - fifo_no) * (int64_t)fifo_period;
		ts->timestamp = ts->it.up - interval;
	}
}
EXPORT_SYMBOL_NS_GPL(inv_sensors_timestamp_apply_odr, IIO_INV_SENSORS_TIMESTAMP);

MODULE_AUTHOR("InvenSense, Inc.");
MODULE_DESCRIPTION("InvenSense sensors timestamp module");
MODULE_LICENSE("GPL");