diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index b190846c3dc261e3193ac85f5def8aaba523f2dc..52eb46ef84c1b21958803dd0ac4401c58542f725 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -30,6 +30,9 @@ config IIO_CONFIGFS
(e.g. software triggers). For more info see
Documentation/iio/iio_configfs.rst.
+config IIO_GTS_HELPER
+ tristate
+
config IIO_TRIGGER
bool "Enable triggered sampling support"
help
diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
index 3be08cdadd7e56bf70bc6bfb75cadf12a61510b5..9622347a1c1befb78ce9fb92975760c8a31cfcea 100644
--- a/drivers/iio/Makefile
+++ b/drivers/iio/Makefile
@@ -9,6 +9,7 @@ industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
+obj-$(CONFIG_IIO_GTS_HELPER) += industrialio-gts-helper.o
obj-$(CONFIG_IIO_SW_DEVICE) += industrialio-sw-device.o
obj-$(CONFIG_IIO_SW_TRIGGER) += industrialio-sw-trigger.o
obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
diff --git a/drivers/iio/industrialio-gts-helper.c b/drivers/iio/industrialio-gts-helper.c
new file mode 100644
index 0000000000000000000000000000000000000000..8bb68975b2598a48682af26d798b0af9340de311
--- /dev/null
+++ b/drivers/iio/industrialio-gts-helper.c
@@ -0,0 +1,1077 @@
+// 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;
+ int tmp = 1;
+
+ if (scale > full || !scale)
+ return -EINVAL;
+
+ if (U64_MAX - full < scale) {
+ /* Risk of overflow */
+ if (full - scale < scale)
+ return 1;
+
+ full -= scale;
+ tmp++;
+ }
+
+ while (full > scale * (u64)tmp)
+ tmp++;
+
+ return tmp;
+}
+
+/**
+ * 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->num_hwgain, sizeof(int));
+ all_gains = kcalloc(gts->num_itime, gain_bytes, GFP_KERNEL);
+ if (!all_gains)
+ return -ENOMEM;
+
+ /*
+ * We assume all the gains for same integration time were unique.
+ * It is likely the first time table had greatest time multiplier as
+ * the times are in the order of preference and greater times are
+ * usually preferred. Hence we start from the last table which is likely
+ * to have the smallest total gains.
+ */
+ time_idx = gts->num_itime - 1;
+ memcpy(all_gains, gains[time_idx], gain_bytes);
+ new_idx = gts->num_hwgain;
+
+ while (time_idx--) {
+ for (j = 0; j < gts->num_hwgain; j++) {
+ int candidate = gains[time_idx][j];
+ int chk;
+
+ if (candidate > all_gains[new_idx - 1]) {
+ all_gains[new_idx] = candidate;
+ new_idx++;
+
+ continue;
+ }
+ for (chk = 0; chk < new_idx; chk++)
+ if (candidate <= all_gains[chk])
+ break;
+
+ if (candidate == all_gains[chk])
+ continue;
+
+ memmove(&all_gains[chk + 1], &all_gains[chk],
+ (new_idx - chk) * sizeof(int));
+ all_gains[chk] = candidate;
+ new_idx++;
+ }
+ }
+
+ gts->avail_all_scales_table = kcalloc(new_idx, 2 * sizeof(int),
+ GFP_KERNEL);
+ if (!gts->avail_all_scales_table) {
+ ret = -ENOMEM;
+ goto free_out;
+ }
+ gts->num_avail_all_scales = new_idx;
+
+ for (i = 0; i < gts->num_avail_all_scales; i++) {
+ ret = iio_gts_total_gain_to_scale(gts, all_gains[i],
+ >s->avail_all_scales_table[i * 2],
+ >s->avail_all_scales_table[i * 2 + 1]);
+
+ if (ret) {
+ kfree(gts->avail_all_scales_table);
+ gts->num_avail_all_scales = 0;
+ goto free_out;
+ }
+ }
+
+free_out:
+ kfree(all_gains);
+
+ return ret;
+}
+
+/**
+ * iio_gts_build_avail_scale_table - create tables of available scales
+ * @gts: Gain time scale descriptor
+ *
+ * Build the tables which can represent the available scales based on the
+ * originally given gain and time tables. When both time and gain tables are
+ * given this results:
+ * 1. A set of tables representing available scales for each supported
+ * integration time.
+ * 2. A single table listing all the unique scales that any combination of
+ * supported gains and times can provide.
+ *
+ * NOTE: Space allocated for the tables must be freed using
+ * iio_gts_purge_avail_scale_table() when the tables are no longer needed.
+ *
+ * Return: 0 on success.
+ */
+static int iio_gts_build_avail_scale_table(struct iio_gts *gts)
+{
+ int **per_time_gains, **per_time_scales, i, j, ret = -ENOMEM;
+
+ per_time_gains = kcalloc(gts->num_itime, sizeof(*per_time_gains), GFP_KERNEL);
+ if (!per_time_gains)
+ return ret;
+
+ per_time_scales = kcalloc(gts->num_itime, sizeof(*per_time_scales), GFP_KERNEL);
+ if (!per_time_scales)
+ goto free_gains;
+
+ for (i = 0; i < gts->num_itime; i++) {
+ per_time_scales[i] = kcalloc(gts->num_hwgain, 2 * sizeof(int),
+ GFP_KERNEL);
+ if (!per_time_scales[i])
+ goto err_free_out;
+
+ per_time_gains[i] = kcalloc(gts->num_hwgain, sizeof(int),
+ GFP_KERNEL);
+ if (!per_time_gains[i]) {
+ kfree(per_time_scales[i]);
+ goto err_free_out;
+ }
+
+ for (j = 0; j < gts->num_hwgain; j++)
+ per_time_gains[i][j] = gts->hwgain_table[j].gain *
+ gts->itime_table[i].mul;
+ }
+
+ ret = gain_to_scaletables(gts, per_time_gains, per_time_scales);
+ if (ret)
+ goto err_free_out;
+
+ kfree(per_time_gains);
+ gts->per_time_avail_scale_tables = per_time_scales;
+
+ return 0;
+
+err_free_out:
+ for (i--; i; i--) {
+ kfree(per_time_scales[i]);
+ kfree(per_time_gains[i]);
+ }
+ kfree(per_time_scales);
+free_gains:
+ kfree(per_time_gains);
+
+ return ret;
+}
+
+/**
+ * iio_gts_build_avail_time_table - build table of available integration times
+ * @gts: Gain time scale descriptor
+ *
+ * Build the table which can represent the available times to be returned
+ * to users using the read_avail-callback.
+ *
+ * NOTE: Space allocated for the tables must be freed using
+ * iio_gts_purge_avail_time_table() when the tables are no longer needed.
+ *
+ * Return: 0 on success.
+ */
+static int iio_gts_build_avail_time_table(struct iio_gts *gts)
+{
+ int *times, i, j, idx = 0;
+
+ if (!gts->num_itime)
+ return 0;
+
+ times = kcalloc(gts->num_itime, sizeof(int), GFP_KERNEL);
+ if (!times)
+ return -ENOMEM;
+
+ /* Sort times from all tables to one and remove duplicates */
+ for (i = gts->num_itime - 1; i >= 0; i--) {
+ int new = gts->itime_table[i].time_us;
+
+ if (times[idx] < new) {
+ times[idx++] = new;
+ continue;
+ }
+
+ for (j = 0; j <= idx; j++) {
+ if (times[j] > new) {
+ memmove(×[j + 1], ×[j],
+ (idx - j) * sizeof(int));
+ times[j] = new;
+ idx++;
+ }
+ }
+ }
+ gts->avail_time_tables = times;
+ /*
+ * This is just to survive a unlikely corner-case where times in the
+ * given time table were not unique. Else we could just trust the
+ * gts->num_itime.
+ */
+ gts->num_avail_time_tables = idx;
+
+ return 0;
+}
+
+/**
+ * iio_gts_purge_avail_time_table - free-up the available integration time table
+ * @gts: Gain time scale descriptor
+ *
+ * Free the space reserved by iio_gts_build_avail_time_table().
+ */
+static void iio_gts_purge_avail_time_table(struct iio_gts *gts)
+{
+ if (gts->num_avail_time_tables) {
+ kfree(gts->avail_time_tables);
+ gts->avail_time_tables = NULL;
+ gts->num_avail_time_tables = 0;
+ }
+}
+
+/**
+ * iio_gts_build_avail_tables - create tables of available scales and int times
+ * @gts: Gain time scale descriptor
+ *
+ * Build the tables which can represent the available scales and available
+ * integration times. Availability tables are built based on the originally
+ * given gain and given time tables.
+ *
+ * When both time and gain tables are
+ * given this results:
+ * 1. A set of sorted tables representing available scales for each supported
+ * integration time.
+ * 2. A single sorted table listing all the unique scales that any combination
+ * of supported gains and times can provide.
+ * 3. A sorted table of supported integration times
+ *
+ * After these tables are built one can use the iio_gts_all_avail_scales(),
+ * iio_gts_avail_scales_for_time() and iio_gts_avail_times() helpers to
+ * implement the read_avail operations.
+ *
+ * NOTE: Space allocated for the tables must be freed using
+ * iio_gts_purge_avail_tables() when the tables are no longer needed.
+ *
+ * Return: 0 on success.
+ */
+static int iio_gts_build_avail_tables(struct iio_gts *gts)
+{
+ int ret;
+
+ ret = iio_gts_build_avail_scale_table(gts);
+ if (ret)
+ return ret;
+
+ ret = iio_gts_build_avail_time_table(gts);
+ if (ret)
+ iio_gts_purge_avail_scale_table(gts);
+
+ return ret;
+}
+
+/**
+ * iio_gts_purge_avail_tables - free-up the availability tables
+ * @gts: Gain time scale descriptor
+ *
+ * Free the space reserved by iio_gts_build_avail_tables(). Frees both the
+ * integration time and scale tables.
+ */
+static void iio_gts_purge_avail_tables(struct iio_gts *gts)
+{
+ iio_gts_purge_avail_time_table(gts);
+ iio_gts_purge_avail_scale_table(gts);
+}
+
+static void devm_iio_gts_avail_all_drop(void *res)
+{
+ iio_gts_purge_avail_tables(res);
+}
+
+/**
+ * devm_iio_gts_build_avail_tables - manged add availability tables
+ * @dev: Pointer to the device whose lifetime tables are bound
+ * @gts: Gain time scale descriptor
+ *
+ * Build the tables which can represent the available scales and available
+ * integration times. Availability tables are built based on the originally
+ * given gain and given time tables.
+ *
+ * When both time and gain tables are given this results:
+ * 1. A set of sorted tables representing available scales for each supported
+ * integration time.
+ * 2. A single sorted table listing all the unique scales that any combination
+ * of supported gains and times can provide.
+ * 3. A sorted table of supported integration times
+ *
+ * After these tables are built one can use the iio_gts_all_avail_scales(),
+ * iio_gts_avail_scales_for_time() and iio_gts_avail_times() helpers to
+ * implement the read_avail operations.
+ *
+ * The tables are automatically released upon device detach.
+ *
+ * Return: 0 on success.
+ */
+static int devm_iio_gts_build_avail_tables(struct device *dev,
+ struct iio_gts *gts)
+{
+ int ret;
+
+ ret = iio_gts_build_avail_tables(gts);
+ if (ret)
+ return ret;
+
+ return devm_add_action_or_reset(dev, devm_iio_gts_avail_all_drop, gts);
+}
+
+static int sanity_check_time(const struct iio_itime_sel_mul *t)
+{
+ if (t->sel < 0 || t->time_us < 0 || t->mul <= 0)
+ return -EINVAL;
+
+ return 0;
+}
+
+static int sanity_check_gain(const struct iio_gain_sel_pair *g)
+{
+ if (g->sel < 0 || g->gain <= 0)
+ return -EINVAL;
+
+ return 0;
+}
+
+static int iio_gts_sanity_check(struct iio_gts *gts)
+{
+ int g, t, ret;
+
+ if (!gts->num_hwgain && !gts->num_itime)
+ return -EINVAL;
+
+ for (t = 0; t < gts->num_itime; t++) {
+ ret = sanity_check_time(>s->itime_table[t]);
+ if (ret)
+ return ret;
+ }
+
+ for (g = 0; g < gts->num_hwgain; g++) {
+ ret = sanity_check_gain(>s->hwgain_table[g]);
+ if (ret)
+ return ret;
+ }
+
+ for (g = 0; g < gts->num_hwgain; g++) {
+ for (t = 0; t < gts->num_itime; t++) {
+ int gain, mul, res;
+
+ gain = gts->hwgain_table[g].gain;
+ mul = gts->itime_table[t].mul;
+
+ if (check_mul_overflow(gain, mul, &res))
+ return -EOVERFLOW;
+ }
+ }
+
+ return 0;
+}
+
+static int iio_init_iio_gts(int max_scale_int, int max_scale_nano,
+ const struct iio_gain_sel_pair *gain_tbl, int num_gain,
+ const struct iio_itime_sel_mul *tim_tbl, int num_times,
+ struct iio_gts *gts)
+{
+ int ret;
+
+ memset(gts, 0, sizeof(*gts));
+
+ ret = iio_gts_linearize(max_scale_int, max_scale_nano, NANO,
+ >s->max_scale);
+ if (ret)
+ return ret;
+
+ gts->hwgain_table = gain_tbl;
+ gts->num_hwgain = num_gain;
+ gts->itime_table = tim_tbl;
+ gts->num_itime = num_times;
+
+ return iio_gts_sanity_check(gts);
+}
+
+/**
+ * devm_iio_init_iio_gts - Initialize the gain-time-scale helper
+ * @dev: Pointer to the device whose lifetime gts resources are
+ * bound
+ * @max_scale_int: integer part of the maximum scale value
+ * @max_scale_nano: fraction part of the maximum scale value
+ * @gain_tbl: table describing supported gains
+ * @num_gain: number of gains in the gain table
+ * @tim_tbl: table describing supported integration times. Provide
+ * the integration time table sorted so that the preferred
+ * integration time is in the first array index. The search
+ * functions like the
+ * iio_gts_find_time_and_gain_sel_for_scale() start search
+ * from first provided time.
+ * @num_times: number of times in the time table
+ * @gts: pointer to the helper struct
+ *
+ * Initialize the gain-time-scale helper for use. Note, gains, times, selectors
+ * and multipliers must be positive. Negative values are reserved for error
+ * checking. The total gain (maximum gain * maximum time multiplier) must not
+ * overflow int. The allocated resources will be released upon device detach.
+ *
+ * Return: 0 on success.
+ */
+int devm_iio_init_iio_gts(struct device *dev, int max_scale_int, int max_scale_nano,
+ const struct iio_gain_sel_pair *gain_tbl, int num_gain,
+ const struct iio_itime_sel_mul *tim_tbl, int num_times,
+ struct iio_gts *gts)
+{
+ int ret;
+
+ ret = iio_init_iio_gts(max_scale_int, max_scale_nano, gain_tbl,
+ num_gain, tim_tbl, num_times, gts);
+ if (ret)
+ return ret;
+
+ return devm_iio_gts_build_avail_tables(dev, gts);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_init_iio_gts, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_all_avail_scales - helper for listing all available scales
+ * @gts: Gain time scale descriptor
+ * @vals: Returned array of supported scales
+ * @type: Type of returned scale values
+ * @length: Amount of returned values in array
+ *
+ * Return: a value suitable to be returned from read_avail or a negative error.
+ */
+int iio_gts_all_avail_scales(struct iio_gts *gts, const int **vals, int *type,
+ int *length)
+{
+ if (!gts->num_avail_all_scales)
+ return -EINVAL;
+
+ *vals = gts->avail_all_scales_table;
+ *type = IIO_VAL_INT_PLUS_NANO;
+ *length = gts->num_avail_all_scales * 2;
+
+ return IIO_AVAIL_LIST;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_all_avail_scales, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_avail_scales_for_time - list scales for integration time
+ * @gts: Gain time scale descriptor
+ * @time: Integration time for which the scales are listed
+ * @vals: Returned array of supported scales
+ * @type: Type of returned scale values
+ * @length: Amount of returned values in array
+ *
+ * Drivers which do not allow scale setting to change integration time can
+ * use this helper to list only the scales which are valid for given integration
+ * time.
+ *
+ * Return: a value suitable to be returned from read_avail or a negative error.
+ */
+int iio_gts_avail_scales_for_time(struct iio_gts *gts, int time,
+ const int **vals, int *type, int *length)
+{
+ int i;
+
+ for (i = 0; i < gts->num_itime; i++)
+ if (gts->itime_table[i].time_us == time)
+ break;
+
+ if (i == gts->num_itime)
+ return -EINVAL;
+
+ *vals = gts->per_time_avail_scale_tables[i];
+ *type = IIO_VAL_INT_PLUS_NANO;
+ *length = gts->num_hwgain * 2;
+
+ return IIO_AVAIL_LIST;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_avail_scales_for_time, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_avail_times - helper for listing available integration times
+ * @gts: Gain time scale descriptor
+ * @vals: Returned array of supported times
+ * @type: Type of returned scale values
+ * @length: Amount of returned values in array
+ *
+ * Return: a value suitable to be returned from read_avail or a negative error.
+ */
+int iio_gts_avail_times(struct iio_gts *gts, const int **vals, int *type,
+ int *length)
+{
+ if (!gts->num_avail_time_tables)
+ return -EINVAL;
+
+ *vals = gts->avail_time_tables;
+ *type = IIO_VAL_INT;
+ *length = gts->num_avail_time_tables;
+
+ return IIO_AVAIL_LIST;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_avail_times, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_find_sel_by_gain - find selector corresponding to a HW-gain
+ * @gts: Gain time scale descriptor
+ * @gain: HW-gain for which matching selector is searched for
+ *
+ * Return: a selector matching given HW-gain or -EINVAL if selector was
+ * not found.
+ */
+int iio_gts_find_sel_by_gain(struct iio_gts *gts, int gain)
+{
+ int i;
+
+ for (i = 0; i < gts->num_hwgain; i++)
+ if (gts->hwgain_table[i].gain == gain)
+ return gts->hwgain_table[i].sel;
+
+ return -EINVAL;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_find_sel_by_gain, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_find_gain_by_sel - find HW-gain corresponding to a selector
+ * @gts: Gain time scale descriptor
+ * @sel: selector for which matching HW-gain is searched for
+ *
+ * Return: a HW-gain matching given selector or -EINVAL if HW-gain was not
+ * found.
+ */
+int iio_gts_find_gain_by_sel(struct iio_gts *gts, int sel)
+{
+ int i;
+
+ for (i = 0; i < gts->num_hwgain; i++)
+ if (gts->hwgain_table[i].sel == sel)
+ return gts->hwgain_table[i].gain;
+
+ return -EINVAL;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_find_gain_by_sel, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_get_min_gain - find smallest valid HW-gain
+ * @gts: Gain time scale descriptor
+ *
+ * Return: The smallest HW-gain -EINVAL if no HW-gains were in the tables.
+ */
+int iio_gts_get_min_gain(struct iio_gts *gts)
+{
+ int i, min = -EINVAL;
+
+ for (i = 0; i < gts->num_hwgain; i++) {
+ int gain = gts->hwgain_table[i].gain;
+
+ if (min == -EINVAL)
+ min = gain;
+ else
+ min = min(min, gain);
+ }
+
+ return min;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_get_min_gain, IIO_GTS_HELPER);
+
+/**
+ * iio_find_closest_gain_low - Find the closest lower matching gain
+ * @gts: Gain time scale descriptor
+ * @gain: HW-gain for which the closest match is searched
+ * @in_range: indicate if the @gain was actually in the range of
+ * supported gains.
+ *
+ * Search for closest supported gain that is lower than or equal to the
+ * gain given as a parameter. This is usable for drivers which do not require
+ * user to request exact matching gain but rather for rounding to a supported
+ * gain value which is equal or lower (setting lower gain is typical for
+ * avoiding saturation)
+ *
+ * Return: The closest matching supported gain or -EINVAL if @gain
+ * was smaller than the smallest supported gain.
+ */
+int iio_find_closest_gain_low(struct iio_gts *gts, int gain, bool *in_range)
+{
+ int i, diff = 0;
+ int best = -1;
+
+ *in_range = false;
+
+ for (i = 0; i < gts->num_hwgain; i++) {
+ if (gain == gts->hwgain_table[i].gain) {
+ *in_range = true;
+ return gain;
+ }
+
+ if (gain > gts->hwgain_table[i].gain) {
+ if (!diff) {
+ diff = gain - gts->hwgain_table[i].gain;
+ best = i;
+ } else {
+ int tmp = gain - gts->hwgain_table[i].gain;
+
+ if (tmp < diff) {
+ diff = tmp;
+ best = i;
+ }
+ }
+ } else {
+ /*
+ * We found valid HW-gain which is greater than
+ * reference. So, unless we return a failure below we
+ * will have found an in-range gain
+ */
+ *in_range = true;
+ }
+ }
+ /* The requested gain was smaller than anything we support */
+ if (!diff) {
+ *in_range = false;
+
+ return -EINVAL;
+ }
+
+ return gts->hwgain_table[best].gain;
+}
+EXPORT_SYMBOL_NS_GPL(iio_find_closest_gain_low, IIO_GTS_HELPER);
+
+static int iio_gts_get_int_time_gain_multiplier_by_sel(struct iio_gts *gts,
+ int sel)
+{
+ const struct iio_itime_sel_mul *time;
+
+ time = iio_gts_find_itime_by_sel(gts, sel);
+ if (!time)
+ return -EINVAL;
+
+ return time->mul;
+}
+
+/**
+ * iio_gts_find_gain_for_scale_using_time - Find gain by time and scale
+ * @gts: Gain time scale descriptor
+ * @time_sel: Integration time selector corresponding to the time gain is
+ * searched for
+ * @scale_int: Integral part of the scale (typically val1)
+ * @scale_nano: Fractional part of the scale (nano or ppb)
+ * @gain: Pointer to value where gain is stored.
+ *
+ * In some cases the light sensors may want to find a gain setting which
+ * corresponds given scale and integration time. Sensors which fill the
+ * gain and time tables may use this helper to retrieve the gain.
+ *
+ * Return: 0 on success. -EINVAL if gain matching the parameters is not
+ * found.
+ */
+static int iio_gts_find_gain_for_scale_using_time(struct iio_gts *gts, int time_sel,
+ int scale_int, int scale_nano,
+ int *gain)
+{
+ u64 scale_linear;
+ int ret, mul;
+
+ ret = iio_gts_linearize(scale_int, scale_nano, NANO, &scale_linear);
+ if (ret)
+ return ret;
+
+ ret = iio_gts_get_int_time_gain_multiplier_by_sel(gts, time_sel);
+ if (ret < 0)
+ return ret;
+
+ mul = ret;
+
+ ret = gain_get_scale_fraction(gts->max_scale, scale_linear, mul, gain);
+ if (ret)
+ return ret;
+
+ if (!iio_gts_valid_gain(gts, *gain))
+ return -EINVAL;
+
+ return 0;
+}
+
+/**
+ * iio_gts_find_gain_sel_for_scale_using_time - Fetch gain selector.
+ * @gts: Gain time scale descriptor
+ * @time_sel: Integration time selector corresponding to the time gain is
+ * searched for
+ * @scale_int: Integral part of the scale (typically val1)
+ * @scale_nano: Fractional part of the scale (nano or ppb)
+ * @gain_sel: Pointer to value where gain selector is stored.
+ *
+ * See iio_gts_find_gain_for_scale_using_time() for more information
+ */
+int iio_gts_find_gain_sel_for_scale_using_time(struct iio_gts *gts, int time_sel,
+ int scale_int, int scale_nano,
+ int *gain_sel)
+{
+ int gain, ret;
+
+ ret = iio_gts_find_gain_for_scale_using_time(gts, time_sel, scale_int,
+ scale_nano, &gain);
+ if (ret)
+ return ret;
+
+ ret = iio_gts_find_sel_by_gain(gts, gain);
+ if (ret < 0)
+ return ret;
+
+ *gain_sel = ret;
+
+ return 0;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_find_gain_sel_for_scale_using_time, IIO_GTS_HELPER);
+
+static int iio_gts_get_total_gain(struct iio_gts *gts, int gain, int time)
+{
+ const struct iio_itime_sel_mul *itime;
+
+ if (!iio_gts_valid_gain(gts, gain))
+ return -EINVAL;
+
+ if (!gts->num_itime)
+ return gain;
+
+ itime = iio_gts_find_itime_by_time(gts, time);
+ if (!itime)
+ return -EINVAL;
+
+ return gain * itime->mul;
+}
+
+static int iio_gts_get_scale_linear(struct iio_gts *gts, int gain, int time,
+ u64 *scale)
+{
+ int total_gain;
+ u64 tmp;
+
+ total_gain = iio_gts_get_total_gain(gts, gain, time);
+ if (total_gain < 0)
+ return total_gain;
+
+ tmp = gts->max_scale;
+
+ do_div(tmp, total_gain);
+
+ *scale = tmp;
+
+ return 0;
+}
+
+/**
+ * iio_gts_get_scale - get scale based on integration time and HW-gain
+ * @gts: Gain time scale descriptor
+ * @gain: HW-gain for which the scale is computed
+ * @time: Integration time for which the scale is computed
+ * @scale_int: Integral part of the scale (typically val1)
+ * @scale_nano: Fractional part of the scale (nano or ppb)
+ *
+ * Compute scale matching the integration time and HW-gain given as parameter.
+ *
+ * Return: 0 on success.
+ */
+int iio_gts_get_scale(struct iio_gts *gts, int gain, int time, int *scale_int,
+ int *scale_nano)
+{
+ u64 lin_scale;
+ int ret;
+
+ ret = iio_gts_get_scale_linear(gts, gain, time, &lin_scale);
+ if (ret)
+ return ret;
+
+ return iio_gts_delinearize(lin_scale, NANO, scale_int, scale_nano);
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_get_scale, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_find_new_gain_sel_by_old_gain_time - compensate for time change
+ * @gts: Gain time scale descriptor
+ * @old_gain: Previously set gain
+ * @old_time_sel: Selector corresponding previously set time
+ * @new_time_sel: Selector corresponding new time to be set
+ * @new_gain: Pointer to value where new gain is to be written
+ *
+ * We may want to mitigate the scale change caused by setting a new integration
+ * time (for a light sensor) by also updating the (HW)gain. This helper computes
+ * new gain value to maintain the scale with new integration time.
+ *
+ * Return: 0 if an exactly matching supported new gain was found. When a
+ * non-zero value is returned, the @new_gain will be set to a negative or
+ * positive value. The negative value means that no gain could be computed.
+ * Positive value will be the "best possible new gain there could be". There
+ * can be two reasons why finding the "best possible" new gain is not deemed
+ * successful. 1) This new value cannot be supported by the hardware. 2) The new
+ * gain required to maintain the scale would not be an integer. In this case,
+ * the "best possible" new gain will be a floored optimal gain, which may or
+ * may not be supported by the hardware.
+ */
+int iio_gts_find_new_gain_sel_by_old_gain_time(struct iio_gts *gts,
+ int old_gain, int old_time_sel,
+ int new_time_sel, int *new_gain)
+{
+ const struct iio_itime_sel_mul *itime_old, *itime_new;
+ u64 scale;
+ int ret;
+
+ *new_gain = -1;
+
+ itime_old = iio_gts_find_itime_by_sel(gts, old_time_sel);
+ if (!itime_old)
+ return -EINVAL;
+
+ itime_new = iio_gts_find_itime_by_sel(gts, new_time_sel);
+ if (!itime_new)
+ return -EINVAL;
+
+ ret = iio_gts_get_scale_linear(gts, old_gain, itime_old->time_us,
+ &scale);
+ if (ret)
+ return ret;
+
+ ret = gain_get_scale_fraction(gts->max_scale, scale, itime_new->mul,
+ new_gain);
+ if (ret)
+ return ret;
+
+ if (!iio_gts_valid_gain(gts, *new_gain))
+ return -EINVAL;
+
+ return 0;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_find_new_gain_sel_by_old_gain_time, IIO_GTS_HELPER);
+
+/**
+ * iio_gts_find_new_gain_by_old_gain_time - compensate for time change
+ * @gts: Gain time scale descriptor
+ * @old_gain: Previously set gain
+ * @old_time: Selector corresponding previously set time
+ * @new_time: Selector corresponding new time to be set
+ * @new_gain: Pointer to value where new gain is to be written
+ *
+ * We may want to mitigate the scale change caused by setting a new integration
+ * time (for a light sensor) by also updating the (HW)gain. This helper computes
+ * new gain value to maintain the scale with new integration time.
+ *
+ * Return: 0 if an exactly matching supported new gain was found. When a
+ * non-zero value is returned, the @new_gain will be set to a negative or
+ * positive value. The negative value means that no gain could be computed.
+ * Positive value will be the "best possible new gain there could be". There
+ * can be two reasons why finding the "best possible" new gain is not deemed
+ * successful. 1) This new value cannot be supported by the hardware. 2) The new
+ * gain required to maintain the scale would not be an integer. In this case,
+ * the "best possible" new gain will be a floored optimal gain, which may or
+ * may not be supported by the hardware.
+ */
+int iio_gts_find_new_gain_by_old_gain_time(struct iio_gts *gts, int old_gain,
+ int old_time, int new_time,
+ int *new_gain)
+{
+ const struct iio_itime_sel_mul *itime_new;
+ u64 scale;
+ int ret;
+
+ *new_gain = -1;
+
+ itime_new = iio_gts_find_itime_by_time(gts, new_time);
+ if (!itime_new)
+ return -EINVAL;
+
+ ret = iio_gts_get_scale_linear(gts, old_gain, old_time, &scale);
+ if (ret)
+ return ret;
+
+ ret = gain_get_scale_fraction(gts->max_scale, scale, itime_new->mul,
+ new_gain);
+ if (ret)
+ return ret;
+
+ if (!iio_gts_valid_gain(gts, *new_gain))
+ return -EINVAL;
+
+ return 0;
+}
+EXPORT_SYMBOL_NS_GPL(iio_gts_find_new_gain_by_old_gain_time, IIO_GTS_HELPER);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Matti Vaittinen <mazziesaccount@gmail.com>");
+MODULE_DESCRIPTION("IIO light sensor gain-time-scale helpers");
diff --git a/include/linux/iio/iio-gts-helper.h b/include/linux/iio/iio-gts-helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..dd64e544a3daa8f1be15d8a47742bf54317d982e
--- /dev/null
+++ b/include/linux/iio/iio-gts-helper.h
@@ -0,0 +1,206 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* gain-time-scale conversion helpers for IIO light sensors
+ *
+ * Copyright (c) 2023 Matti Vaittinen <mazziesaccount@gmail.com>
+ */
+
+#ifndef __IIO_GTS_HELPER__
+#define __IIO_GTS_HELPER__
+
+#include <linux/types.h>
+
+struct device;
+
+/**
+ * struct iio_gain_sel_pair - gain - selector values
+ *
+ * In many cases devices like light sensors allow setting signal amplification
+ * (gain) using a register interface. This structure describes amplification
+ * and corresponding selector (register value)
+ *
+ * @gain: Gain (multiplication) value. Gain must be positive, negative
+ * values are reserved for error handling.
+ * @sel: Selector (usually register value) used to indicate this gain.
+ * NOTE: Only selectors >= 0 supported.
+ */
+struct iio_gain_sel_pair {
+ int gain;
+ int sel;
+};
+
+/**
+ * struct iio_itime_sel_mul - integration time description
+ *
+ * In many cases devices like light sensors allow setting the duration of
+ * collecting data. Typically this duration has also an impact to the magnitude
+ * of measured values (gain). This structure describes the relation of
+ * integration time and amplification as well as corresponding selector
+ * (register value).
+ *
+ * An example could be a sensor allowing 50, 100, 200 and 400 mS times. The
+ * respective multiplication values could be 50 mS => 1, 100 mS => 2,
+ * 200 mS => 4 and 400 mS => 8 assuming the impact of integration time would be
+ * linear in a way that when collecting data for 50 mS caused value X, doubling
+ * the data collection time caused value 2X etc.
+ *
+ * @time_us: Integration time in microseconds. Time values must be positive,
+ * negative values are reserved for error handling.
+ * @sel: Selector (usually register value) used to indicate this time
+ * NOTE: Only selectors >= 0 supported.
+ * @mul: Multiplication to the values caused by this time.
+ * NOTE: Only multipliers > 0 supported.
+ */
+struct iio_itime_sel_mul {
+ int time_us;
+ int sel;
+ int mul;
+};
+
+struct iio_gts {
+ u64 max_scale;
+ const struct iio_gain_sel_pair *hwgain_table;
+ int num_hwgain;
+ const struct iio_itime_sel_mul *itime_table;
+ int num_itime;
+ int **per_time_avail_scale_tables;
+ int *avail_all_scales_table;
+ int num_avail_all_scales;
+ int *avail_time_tables;
+ int num_avail_time_tables;
+};
+
+#define GAIN_SCALE_GAIN(_gain, _sel) \
+{ \
+ .gain = (_gain), \
+ .sel = (_sel), \
+}
+
+#define GAIN_SCALE_ITIME_US(_itime, _sel, _mul) \
+{ \
+ .time_us = (_itime), \
+ .sel = (_sel), \
+ .mul = (_mul), \
+}
+
+static inline const struct iio_itime_sel_mul *
+iio_gts_find_itime_by_time(struct iio_gts *gts, int time)
+{
+ int i;
+
+ if (!gts->num_itime)
+ return NULL;
+
+ for (i = 0; i < gts->num_itime; i++)
+ if (gts->itime_table[i].time_us == time)
+ return >s->itime_table[i];
+
+ return NULL;
+}
+
+static inline const struct iio_itime_sel_mul *
+iio_gts_find_itime_by_sel(struct iio_gts *gts, int sel)
+{
+ int i;
+
+ for (i = 0; i < gts->num_itime; i++)
+ if (gts->itime_table[i].sel == sel)
+ return >s->itime_table[i];
+
+ return NULL;
+}
+
+int devm_iio_init_iio_gts(struct device *dev, int max_scale_int, int max_scale_nano,
+ const struct iio_gain_sel_pair *gain_tbl, int num_gain,
+ const struct iio_itime_sel_mul *tim_tbl, int num_times,
+ struct iio_gts *gts);
+/**
+ * iio_gts_find_int_time_by_sel - find integration time matching a selector
+ * @gts: Gain time scale descriptor
+ * @sel: selector for which matching integration time is searched for
+ *
+ * Return: integration time matching given selector or -EINVAL if
+ * integration time was not found.
+ */
+static inline int iio_gts_find_int_time_by_sel(struct iio_gts *gts, int sel)
+{
+ const struct iio_itime_sel_mul *itime;
+
+ itime = iio_gts_find_itime_by_sel(gts, sel);
+ if (!itime)
+ return -EINVAL;
+
+ return itime->time_us;
+}
+
+/**
+ * iio_gts_find_sel_by_int_time - find selector matching integration time
+ * @gts: Gain time scale descriptor
+ * @gain: HW-gain for which matching selector is searched for
+ *
+ * Return: a selector matching given integration time or -EINVAL if
+ * selector was not found.
+ */
+static inline int iio_gts_find_sel_by_int_time(struct iio_gts *gts, int time)
+{
+ const struct iio_itime_sel_mul *itime;
+
+ itime = iio_gts_find_itime_by_time(gts, time);
+ if (!itime)
+ return -EINVAL;
+
+ return itime->sel;
+}
+
+/**
+ * iio_gts_valid_time - check if given integration time is valid
+ * @gts: Gain time scale descriptor
+ * @time_us: Integration time to check
+ *
+ * Return: True if given time is supported by device. False if not.
+ */
+static inline bool iio_gts_valid_time(struct iio_gts *gts, int time_us)
+{
+ return iio_gts_find_itime_by_time(gts, time_us) != NULL;
+}
+
+int iio_gts_find_sel_by_gain(struct iio_gts *gts, int gain);
+
+/**
+ * iio_gts_valid_gain - check if given HW-gain is valid
+ * @gts: Gain time scale descriptor
+ * @gain: HW-gain to check
+ *
+ * Return: True if given time is supported by device. False if not.
+ */
+static inline bool iio_gts_valid_gain(struct iio_gts *gts, int gain)
+{
+ return iio_gts_find_sel_by_gain(gts, gain) >= 0;
+}
+
+int iio_find_closest_gain_low(struct iio_gts *gts, int gain, bool *in_range);
+int iio_gts_find_gain_by_sel(struct iio_gts *gts, int sel);
+int iio_gts_get_min_gain(struct iio_gts *gts);
+int iio_gts_find_int_time_by_sel(struct iio_gts *gts, int sel);
+int iio_gts_find_sel_by_int_time(struct iio_gts *gts, int time);
+
+int iio_gts_total_gain_to_scale(struct iio_gts *gts, int total_gain,
+ int *scale_int, int *scale_nano);
+int iio_gts_find_gain_sel_for_scale_using_time(struct iio_gts *gts, int time_sel,
+ int scale_int, int scale_nano,
+ int *gain_sel);
+int iio_gts_get_scale(struct iio_gts *gts, int gain, int time, int *scale_int,
+ int *scale_nano);
+int iio_gts_find_new_gain_sel_by_old_gain_time(struct iio_gts *gts,
+ int old_gain, int old_time_sel,
+ int new_time_sel, int *new_gain);
+int iio_gts_find_new_gain_by_old_gain_time(struct iio_gts *gts, int old_gain,
+ int old_time, int new_time,
+ int *new_gain);
+int iio_gts_avail_times(struct iio_gts *gts, const int **vals, int *type,
+ int *length);
+int iio_gts_all_avail_scales(struct iio_gts *gts, const int **vals, int *type,
+ int *length);
+int iio_gts_avail_scales_for_time(struct iio_gts *gts, int time,
+ const int **vals, int *type, int *length);
+
+#endif