path: root/drivers/iio/industrialio-gts-helper.c

// SPDX-License-Identifier: GPL-2.0-only
/* gain-time-scale conversion helpers for IIO light sensors
 *
 * Copyright (c) 2023 Matti Vaittinen <mazziesaccount@gmail.com>
 */

#include <linux/device.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/minmax.h>
#include <linux/module.h>
#include <linux/overflow.h>
#include <linux/slab.h>
#include <linux/sort.h>
#include <linux/types.h>
#include <linux/units.h>

#include <linux/iio/iio-gts-helper.h>
#include <linux/iio/types.h>

/**
 * iio_gts_get_gain - Convert scale to total gain
 *
 * Internal helper for converting scale to total gain.
 *
 * @max:	Maximum linearized scale. As an example, when scale is created
 *		in magnitude of NANOs and max scale is 64.1 - The linearized
 *		scale is 64 100 000 000.
 * @scale:	Linearized scale to compute the gain for.
 *
 * Return:	(floored) gain corresponding to the scale. -EINVAL if scale
 *		is invalid.
 */
static int iio_gts_get_gain(const u64 max, const u64 scale)
{
	u64 full = max;

	if (scale > full || !scale)
		return -EINVAL;

	return div64_u64(full, scale);
}

/**
 * gain_get_scale_fraction - get the gain or time based on scale and known one
 *
 * @max:	Maximum linearized scale. As an example, when scale is created
 *		in magnitude of NANOs and max scale is 64.1 - The linearized
 *		scale is 64 100 000 000.
 * @scale:	Linearized scale to compute the gain/time for.
 * @known:	Either integration time or gain depending on which one is known
 * @unknown:	Pointer to variable where the computed gain/time is stored
 *
 * Internal helper for computing unknown fraction of total gain.
 * Compute either gain or time based on scale and either the gain or time
 * depending on which one is known.
 *
 * Return:	0 on success.
 */
static int gain_get_scale_fraction(const u64 max, u64 scale, int known,
				   int *unknown)
{
	int tot_gain;

	tot_gain = iio_gts_get_gain(max, scale);
	if (tot_gain < 0)
		return tot_gain;

	*unknown = tot_gain / known;

	/* We require total gain to be exact multiple of known * unknown */
	if (!*unknown || *unknown * known != tot_gain)
		return -EINVAL;

	return 0;
}

static int iio_gts_delinearize(u64 lin_scale, unsigned long scaler,
			       int *scale_whole, int *scale_nano)
{
	int frac;

	if (scaler > NANO)
		return -EOVERFLOW;

	if (!scaler)
		return -EINVAL;

	frac = do_div(lin_scale, scaler);

	*scale_whole = lin_scale;
	*scale_nano = frac * (NANO / scaler);

	return 0;
}

static int iio_gts_linearize(int scale_whole, int scale_nano,
			     unsigned long scaler, u64 *lin_scale)
{
	/*
	 * Expect scale to be (mostly) NANO or MICRO. Divide divider instead of
	 * multiplication followed by division to avoid overflow.
	 */
	if (scaler > NANO || !scaler)
		return -EINVAL;

	*lin_scale = (u64)scale_whole * (u64)scaler +
		     (u64)(scale_nano / (NANO / scaler));

	return 0;
}

/**
 * iio_gts_total_gain_to_scale - convert gain to scale
 * @gts:	Gain time scale descriptor
 * @total_gain:	the gain to be converted
 * @scale_int:	Pointer to integral part of the scale (typically val1)
 * @scale_nano:	Pointer to fractional part of the scale (nano or ppb)
 *
 * Convert the total gain value to scale. NOTE: This does not separate gain
 * generated by HW-gain or integration time. It is up to caller to decide what
 * part of the total gain is due to integration time and what due to HW-gain.
 *
 * Return: 0 on success. Negative errno on failure.
 */
int iio_gts_total_gain_to_scale(struct iio_gts *gts, int total_gain,
				int *scale_int, int *scale_nano)
{
	u64 tmp;

	tmp = gts->max_scale;

	do_div(tmp, total_gain);

	return iio_gts_delinearize(tmp, NANO, scale_int, scale_nano);
}
EXPORT_SYMBOL_NS_GPL(iio_gts_total_gain_to_scale, IIO_GTS_HELPER);

/**
 * iio_gts_purge_avail_scale_table - free-up the available scale tables
 * @gts:	Gain time scale descriptor
 *
 * Free the space reserved by iio_gts_build_avail_scale_table().
 */
static void iio_gts_purge_avail_scale_table(struct iio_gts *gts)
{
	int i;

	if (gts->per_time_avail_scale_tables) {
		for (i = 0; i < gts->num_itime; i++)
			kfree(gts->per_time_avail_scale_tables[i]);

		kfree(gts->per_time_avail_scale_tables);
		gts->per_time_avail_scale_tables = NULL;
	}

	kfree(gts->avail_all_scales_table);
	gts->avail_all_scales_table = NULL;

	gts->num_avail_all_scales = 0;
}

static int iio_gts_gain_cmp(const void *a, const void *b)
{
	return *(int *)a - *(int *)b;
}

static int gain_to_scaletables(struct iio_gts *gts, int **gains, int **scales)
{
	int ret, i, j, new_idx, time_idx;
	int *all_gains;
	size_t gain_bytes;

	for (i = 0; i < gts->num_itime; i++) {
		/*
		 * Sort the tables for nice output and for easier finding of
		 * unique values.
		 */
		sort(gains[i], gts->num_hwgain, sizeof(int), iio_gts_gain_cmp,
		     NULL);

		/* Convert gains to scales */
		for (j = 0; j < gts->num_hwgain; j++) {
			ret = iio_gts_total_gain_to_scale(gts, gains[i][j],
							  &scales[i][2 * j],
							  &scales[i][2 * j + 1]);
			if (ret)
				return ret;
		}
	}

	gain_bytes = array_size(gts->