Some light sensors can adjust both the HW-gain and integration time.
There are cases where adjusting the integration time has similar impact
to the scale of the reported values as gain setting has.
IIO users do typically expect to handle scale by a single writable 'scale'
entry. Driver should then adjust the gain/time accordingly.
It however is difficult for a driver to know whether it should change
gain or integration time to meet the requested scale. Usually it is
preferred to have longer integration time which usually improves
accuracy, but there may be use-cases where long measurement times can be
an issue. Thus it can be preferable to allow also changing the
integration time - but mitigate the scale impact by also changing the gain
underneath. Eg, if integration time change doubles the measured values,
the driver can reduce the HW-gain to half.
The theory of the computations of gain-time-scale is simple. However,
some people (undersigned) got that implemented wrong for more than once.
Add some gain-time-scale helpers in order to not dublicate errors in all
drivers needing these computations.
Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>
---
Currently it is only BU27034 using these in this series. I am however working
with drivers for RGB sensors BU27008 and BU27010 which have similar
[gain - integration time - scale] - relation. I hope sending those
follows soon after the BU27034 is done.
Changes since RFCv1:
- fix include guardian
- Improve kernel doc for iio_init_iio_gts.
- Add iio_gts_scale_to_total_gain
- Add iio_gts_total_gain_to_scale
- Fix review comments from Jonathan
- add documentation to few functions
- replace 0xffffffffffffffffLLU by U64_MAX
- some styling fixes
- drop unnecessary NULL checks
- order function arguments by in / out purpose
- drop GAIN_SCALE_ITIME_MS()
- Add helpers for available scales and times
- Rename to iio-gts-helpers
---
drivers/iio/light/Kconfig | 3 +
drivers/iio/light/Makefile | 1 +
drivers/iio/light/iio-gts-helper.c | 1152 ++++++++++++++++++++++++++++
drivers/iio/light/iio-gts-helper.h | 130 ++++
4 files changed, 1286 insertions(+)
create mode 100644 drivers/iio/light/iio-gts-helper.c
create mode 100644 drivers/iio/light/iio-gts-helper.h
diff --git a/drivers/iio/light/Kconfig b/drivers/iio/light/Kconfig
index 0d4447df7200..671d84f98c56 100644
--- a/drivers/iio/light/Kconfig
+++ b/drivers/iio/light/Kconfig
@@ -183,6 +183,9 @@ config IIO_CROS_EC_LIGHT_PROX
To compile this driver as a module, choose M here:
the module will be called cros_ec_light_prox.
+config IIO_GTS_HELPER
+ tristate
+
config GP2AP002
tristate "Sharp GP2AP002 Proximity/ALS sensor"
depends on I2C
diff --git a/drivers/iio/light/Makefile b/drivers/iio/light/Makefile
index 6f23817fae6f..82d14ebd3c11 100644
--- a/drivers/iio/light/Makefile
+++ b/drivers/iio/light/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_CM3323) += cm3323.o
obj-$(CONFIG_CM3605) += cm3605.o
obj-$(CONFIG_CM36651) += cm36651.o
obj-$(CONFIG_IIO_CROS_EC_LIGHT_PROX) += cros_ec_light_prox.o
+obj-$(CONFIG_IIO_GTS_HELPER) += iio-gts-helper.o
obj-$(CONFIG_GP2AP002) += gp2ap002.o
obj-$(CONFIG_GP2AP020A00F) += gp2ap020a00f.o
obj-$(CONFIG_HID_SENSOR_ALS) += hid-sensor-als.o
diff --git a/drivers/iio/light/iio-gts-helper.c b/drivers/iio/light/iio-gts-helper.c
new file mode 100644
index 000000000000..df6c2fffe775
--- /dev/null
+++ b/drivers/iio/light/iio-gts-helper.c
@@ -0,0 +1,1152 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* gain-time-scale conversion helpers for IIO light sensors
+ *
+ * Copyright (c) 2023 Matti Vaittinen <mazziesaccount@xxxxxxxxx>
+ */
+
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <linux/minmax.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/sort.h>
+#include <linux/units.h>
+
+#include <linux/iio/types.h>
+
+#include "iio-gts-helper.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 creted in
+ * magnitude of NANOs and max scale is 64.1 - The linearized
+ * scale is 64 100 000 000.
+ * @scale: Linearized scale to compte the gain for.
+ *
+ * Return: (floored) gain corresponding to the scales. -EINVAL if scale
+ * is invalid.
+ */
+static int iio_gts_get_gain(const u64 max, const u64 scale)
+{
+ int tmp = 1;
+
+ if (scale > max || !scale)
+ return -EINVAL;
+
+ if (U64_MAX - max < scale) {
+ /* Risk of overflow */
+ if (max - scale < scale)
+ return 1;
+
+ while (max - scale > scale * (u64) tmp)
+ tmp++;
+
+ return tmp + 1;
+ }
+
+ while (max > scale * (u64) tmp)
+ tmp++;
+
+ return tmp;
+}
+/*
+ * gain_get_scale_fraction - get the gain or time based on scale and known one
+ *
+ * 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.
+ *
+ * @max: Maximum linearized scale. As an example, when scale is creted 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
+ *
+ * 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 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 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;
+}
+
+static int iio_gts_delinearize(u64 lin_scale, unsigned long scaler,
+ int *scale_whole, int *scale_nano)
+{
+ int frac;
+
+ if (scaler > NANO || !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
+ * @scale_int: Pointer to integral part of the scale (typically val1)
+ * @scale_nano: Pointer to ractional part of the scale (nano or ppb)
+ * @gain_tot: the gain to be converted
+ *
+ * Convert the total gain value to scale. NOTE: This does not separate gain
+ * generated by hwgain 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_GPL(iio_gts_total_gain_to_scale);
+
+/**
+ * iio_gts_scale_to_total_gain - convert scale to gain
+ * @gts: Gain time scale descriptor
+ * @scale_int: Integral part of the scale (typically val1)
+ * @scale_nano: Fractional part of the scale (nano or ppb)
+ * @gain_tot: pointer to variable where gain is stored
+ *
+ * Convert the scale value to total gain. NOTE: This does not separate gain
+ * generated by hwgain 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_scale_to_total_gain(struct iio_gts *gts, int scale_int,
+ int scale_nano, int *gain_tot)
+{
+ u64 lin_scale;
+ int ret;
+
+ ret = iio_gts_linearize(scale_int, scale_nano, NANO, &lin_scale);
+ if (ret)
+ return ret;
+
+ ret = iio_gts_get_gain(gts->max_scale, lin_scale);
+ if (ret < 0)
+ return ret;
+
+ *gain_tot = ret;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(iio_gts_scale_to_total_gain);
+
+/**
+ * iio_init_iio_gts - Initialize the gain-time-scale helper
+ * @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 gaintable
+ * @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.
+ *
+ * Return: 0 on success.
+ */
+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;
+
+ 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;
+ gts->per_time_avail_scale_tables = NULL;
+ gts->avail_time_tables = NULL;
+ gts->avail_all_scales_table = NULL;
+ gts->num_avail_all_scales = 0;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(iio_init_iio_gts);
+
+/**
+ * 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(). Please note
+ * that the helpers for getting available scales like the
+ * iio_gts_all_avail_scales() are not usable after this call. Thus, this should
+ * be only called after these helpers can no longer be called (Eg. after
+ * the iio-device has been deregistered).
+ */
+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;
+}
+EXPORT_SYMBOL_GPL(iio_gts_purge_avail_scale_table);
+
+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;
+ int *all_gains;
+
+ 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;
+ }
+ }
+
+ all_gains = kcalloc(gts->num_itime * gts->num_hwgain, sizeof(int),
+ 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
+ */
+ memcpy(all_gains, gains[gts->num_itime - 1], gts->num_hwgain * sizeof(int));
+ new_idx = gts->num_hwgain;
+
+ for (i = gts->num_itime - 2; i >= 0; i--)
+ for (j = 0; j < gts->num_hwgain; j++) {
+ int candidate = gains[i][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->num_avail_all_scales = new_idx;
+
+ gts->avail_all_scales_table = kcalloc(gts->num_avail_all_scales,
+ 2 * sizeof(int), GFP_KERNEL);
+ if (!gts->avail_all_scales_table)
+ ret = -ENOMEM;
+ else
+ for (i = 0; !ret && 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]);
+
+ kfree(all_gains);
+ if (ret && gts->avail_all_scales_table)
+ kfree(gts->avail_all_scales_table);
+
+ 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.
+ */
+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(int *), GFP_KERNEL);
+ if (!per_time_gains)
+ return ret;
+
+ per_time_scales = kcalloc(gts->num_itime, sizeof(int *), 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])
+ 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:
+ while (i) {
+ /*
+ * It does not matter if i'th alloc was not succesfull as
+ * kfree(NULL) is safe.
+ */
+ kfree(per_time_gains[i]);
+ kfree(per_time_scales[i]);
+
+ i--;
+ }
+ kfree(per_time_scales);
+free_gains:
+ kfree(per_time_gains);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(iio_gts_build_avail_scale_table);
+
+static inline void devm_iio_gts_avail_scale_drop(void *res)
+{
+ iio_gts_purge_avail_scale_table(res);
+}
+
+/**
+ * devm_iio_gts_build_avail_scale_table - do managed tables of available scales
+ * @gts: Gain time scale descriptor
+ * @dev: Device whose life-time tables are bound to
+ *
+ * Create tables of available scales which are freed upon the device detach.
+ * See the iio_gts_build_avail_scale_table() for more information.
+ *
+ * NOTE: after the tables have been purged, the helpers for getting the
+ * available scales are no longer usable. Care must be taken that unwinding
+ * is done in correct order (iio device is deregistered prior purging the
+ * tables).
+ *
+ * Return: 0 on success.
+ */
+int devm_iio_gts_build_avail_scale_table(struct device *dev,
+ struct iio_gts *gts)
+{
+ int ret;
+
+ ret = iio_gts_build_avail_scale_table(gts);
+ if (ret)
+ return ret;
+
+ return devm_add_action_or_reset(dev, devm_iio_gts_avail_scale_drop, gts);
+}
+EXPORT_SYMBOL_GPL(devm_iio_gts_build_avail_scale_table);
+
+/**
+ * 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.
+ */
+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;
+
+ 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;
+}
+EXPORT_SYMBOL_GPL(iio_gts_build_avail_time_table);
+
+/**
+ * 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(). Please note
+ * that the helpers for getting available integration times like the
+ * iio_gts_avail_times() are not usable after this call. Thus, this should
+ * be only called after these helpers can no longer be called (Eg. after
+ * the iio-device has been deregistered).
+ */
+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;
+ }
+}
+EXPORT_SYMBOL_GPL(iio_gts_purge_avail_time_table);
+
+static inline void devm_iio_gts_avail_time_drop(void *res)
+{
+ iio_gts_purge_avail_time_table(res);
+}
+
+/**
+ * devm_iio_gts_build_avail_time_table - do managed tables of available times
+ * @gts: Gain time scale descriptor
+ * @dev: Device whose life-time tables are bound to
+ *
+ * Create a table of available integration times. Table is freed upon the
+ * device detach. See the iio_gts_build_avail_time_table() for more information.
+ *
+ * NOTE: after the tables have been purged, the helpers for getting
+ * available integration times are no longer usable. Care must be taken that
+ * unwinding is done in correct order (iio device is deregistered prior
+ * purging the tables).
+ *
+ * Return: 0 on success.
+ */
+int devm_iio_gts_build_avail_time_table(struct device *dev, struct iio_gts *gts)
+{
+ int ret;
+
+ if (!gts->num_itime)
+ return 0;
+
+ ret = iio_gts_build_avail_time_table(gts);
+ if (ret)
+ return ret;
+
+ return devm_add_action_or_reset(dev, devm_iio_gts_avail_time_drop, gts);
+}
+EXPORT_SYMBOL_GPL(devm_iio_gts_build_avail_time_table);
+
+/**
+ * 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 opeations.
+ *
+ * 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.
+ */
+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;
+}
+EXPORT_SYMBOL_GPL(iio_gts_build_avail_tables);
+
+/**
+ * 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.
+ *
+ * Note that the helpers for getting available integration times or scales
+ * like the iio_gts_avail_times() are not usable after this call. Thus, this
+ * should be only called after these helpers can no longer be called (Eg.
+ * after the iio-device has been deregistered).
+ */
+void iio_gts_purge_avail_tables(struct iio_gts *gts)
+{
+ iio_gts_purge_avail_time_table(gts);
+ iio_gts_purge_avail_scale_table(gts);
+}
+EXPORT_SYMBOL_GPL(iio_gts_purge_avail_tables);
+
+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
+ * @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 opeations.
+ *
+ * The tables are automatically released upon device detach.
+ *
+ * NOTE: after the tables have been purged, the helpers for getting
+ * available scales / integration times are no longer usable. Care must be
+ * taken that unwinding is done in correct order (iio device is deregistered
+ * prior purging the tables).
+ *
+ * Return: 0 on success.
+ */
+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);
+}
+EXPORT_SYMBOL_GPL(devm_iio_gts_build_avail_tables);
+
+/**
+ * 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
+ *
+ * Returns 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)
+{
+ /*
+ * Using this function prior building the tables is a driver-error
+ * which should be fixed when the driver is tested for a first time
+ */
+ if (WARN_ON(!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_GPL(iio_gts_all_avail_scales);
+
+/**
+ * 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 whic are valid for given integration
+ * time.
+ *
+ * Returns 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_GPL(iio_gts_avail_scales_for_time);
+
+/**
+ * iio_gts_avail_times - helper for listing available integration times
+ * @gts: Gain time scale descriptor
+ * @vals: Returned array of supported timees
+ * @type: Type of returned scale values
+ * @length: Amount of returned values in array
+ *
+ * Returns 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)
+{
+ /*
+ * Using this function prior building the tables is a driver-error
+ * which should be fixed when the driver is tested for a first time
+ */
+ if (WARN_ON(!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_GPL(iio_gts_avail_times);
+
+/**
+ * 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
+ */
+bool iio_gts_valid_time(struct iio_gts *gts, int time_us)
+{
+ return iio_gts_find_itime_by_time(gts, time_us);
+}
+EXPORT_SYMBOL_GPL(iio_gts_valid_time);
+
+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_GPL(iio_gts_find_sel_by_gain);
+
+bool iio_gts_valid_gain(struct iio_gts *gts, int gain)
+{
+ return iio_gts_find_sel_by_gain(gts, gain) >= 0;
+}
+EXPORT_SYMBOL_GPL(iio_gts_valid_gain);
+
+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_GPL(iio_gts_find_gain_by_sel);
+
+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_GPL(iio_gts_get_min_gain);
+
+/**
+ * iio_find_closest_gain_low - Find the closest lower matching gain
+ * @gts: Gain time scale descriptor
+ * @gain: reference gain for which the closest match is searched
+ * @in_range: indicate if the reference 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 fo 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 is reference
+ * 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, min = 0;
+ int best = -1;
+
+ *in_range = false;
+
+ for (i = 0; i < gts->num_hwgain; i++) {
+ /*
+ * It is not expected this function is called for an exactly
+ * matching gain.
+ */
+ if (unlikely(gain == gts->hwgain_table[i].gain)) {
+ *in_range = true;
+ return gain;
+ }
+ if (!min)
+ min = gts->hwgain_table[i].gain;
+ else
+ min = min(min, gts->hwgain_table[i].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 hwgain 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_GPL(iio_find_closest_gain_low);
+
+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;
+}
+EXPORT_SYMBOL_GPL(iio_gts_get_int_time_gain_multiplier_by_sel);
+
+/**
+ * iio_gts_find_gain_for_scale_using_time - Find gain by time and scale
+ * @gts: Gain time scale descriptor
+ * @time_sel: Integration time selector correspondig to the time gain is
+ * searhed 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.
+ */
+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 || !iio_gts_valid_gain(gts, *gain))
+ return -EINVAL;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(iio_gts_find_gain_for_scale_using_time);
+
+/*
+ * iio_gts_find_gain_sel_for_scale_using_time - Fetch gain selector.
+ * 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_GPL(iio_gts_find_gain_sel_for_scale_using_time);
+
+int iio_gts_find_time_and_gain_sel_for_scale(struct iio_gts *gts, int scale_int,
+ int scale_nano, int *gain_sel,
+ int *time_sel)
+{
+ int ret, i;
+
+ for (i = 0; i < gts->num_itime; i++) {
+ *time_sel = gts->itime_table[i].sel;
+ ret = iio_gts_find_gain_sel_for_scale_using_time(gts, *time_sel,
+ scale_int, scale_nano, gain_sel);
+ if (!ret)
+ return 0;
+ }
+
+ return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(iio_gts_find_time_and_gain_sel_for_scale);
+
+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;
+}
+EXPORT_SYMBOL_GPL(iio_gts_find_int_time_by_sel);
+
+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;
+}
+EXPORT_SYMBOL_GPL(iio_gts_find_sel_by_int_time);
+
+int iio_gts_get_total_gain_by_sel(struct iio_gts *gts, int gsel, int tsel)
+{
+ int ret, tmp;
+
+ ret = iio_gts_find_gain_by_sel(gts, gsel);
+ if (ret < 0)
+ return ret;
+
+ tmp = ret;
+
+ /*
+ * TODO: Would these helpers provde any value for cases where we just
+ * use table of gains and no integration time? This would be a standard
+ * format for gain table representation and regval => gain / gain =>
+ * regval conversions. OTOH, a dummy table based conversion is a memory
+ * hog in cases where the gain could be computed simply based on simple
+ * multiplication / bit-shift or by linear_ranges helpers.
+ *
+ * Currently we return an error if int-time table is not populated.
+ */
+ ret = iio_gts_get_int_time_gain_multiplier_by_sel(gts, tsel);
+ if (ret < 0)
+ return ret;
+
+ return tmp * ret;
+}
+EXPORT_SYMBOL_GPL(iio_gts_get_total_gain_by_sel);
+
+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;
+}
+EXPORT_SYMBOL(iio_gts_get_total_gain);
+
+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;
+}
+
+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_GPL(iio_gts_get_scale);
+
+/**
+ * iio_gts_find_new_gain_sel_by_old_gain_time - compensate 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 on success. -EINVAL if gain matching the new time is not found.
+ */
+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;
+
+ 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 -EINVAL;
+
+ if (!iio_gts_valid_gain(gts, *new_gain))
+ return -EINVAL;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(iio_gts_find_new_gain_sel_by_old_gain_time);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Matti Vaittinen <mazziesaccount@xxxxxxxxx>");
+MODULE_DESCRIPTION("IIO light sensor gain-time-scale helpers");
diff --git a/drivers/iio/light/iio-gts-helper.h b/drivers/iio/light/iio-gts-helper.h
new file mode 100644
index 000000000000..7b1f6a0eeb75
--- /dev/null
+++ b/drivers/iio/light/iio-gts-helper.h
@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* gain-time-scale conversion helpers for IIO light sensors
+ *
+ * Copyright (c) 2023 Matti Vaittinen <mazziesaccount@xxxxxxxxx>
+ */
+
+#ifndef __GAIN_TIME_SCALE_HELPER__
+#define __GAIN_TIME_SCALE_HELPER__
+
+/**
+ * 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.
+ * @sel: Selector (usually register value) used to indicate this gain
+ */
+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.
+ * @sel: Selector (usually register value) used to indicate this time
+ * @mul: Multiplication to the values caused by this time.
+ */
+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), \
+}
+
+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);
+
+bool iio_gts_valid_gain(struct iio_gts *gts, int gain);
+bool iio_gts_valid_time(struct iio_gts *gts, int time_us);
+
+int iio_gts_get_total_gain_by_sel(struct iio_gts *gts, int gsel, int tsel);
+int iio_gts_get_total_gain(struct iio_gts *gts, int gain, int time);
+
+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_find_sel_by_gain(struct iio_gts *gts, int gain);
+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_get_int_time_gain_multiplier_by_sel(struct iio_gts *gts,
+ int sel);
+int iio_gts_total_gain_to_scale(struct iio_gts *gts, int total_gain,
+ int *scale_int, int *scale_nano);
+int iio_gts_scale_to_total_gain(struct iio_gts *gts, int scale_int,
+ int scale_nano, int *gain_tot);
+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_find_gain_for_scale_using_time(struct iio_gts *gts, int time_sel,
+ int scale_int, int scale_nano,
+ int *gain);
+int iio_gts_find_time_and_gain_sel_for_scale(struct iio_gts *gts, int scale_int,
+ int scale_nano, int *gain_sel,
+ int *time_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_build_avail_tables(struct iio_gts *gts);
+int devm_iio_gts_build_avail_tables(struct device *dev, struct iio_gts *gts);
+int iio_gts_build_avail_scale_table(struct iio_gts *gts);
+int devm_iio_gts_build_avail_scale_table(struct device *dev, struct iio_gts *gts);
+int iio_gts_build_avail_time_table(struct iio_gts *gts);
+int devm_iio_gts_build_avail_time_table(struct device *dev, struct iio_gts *gts);
+void iio_gts_purge_avail_scale_table(struct iio_gts *gts);
+void iio_gts_purge_avail_time_table(struct iio_gts *gts);
+void iio_gts_purge_avail_tables(struct iio_gts *gts);
+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
--
2.39.2
--
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND
~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =]
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