Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1528 insertions, 0 deletions

diff --git a/drivers/iio/light/rohm-bu27034.c b/drivers/iio/light/rohm-bu27034.c
new file mode 100644
index 0000000000..bf3de853a8
--- /dev/null
+++ b/drivers/iio/light/rohm-bu27034.c
@@ -0,0 +1,1528 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * BU27034 ROHM Ambient Light Sensor
+ *
+ * Copyright (c) 2023, ROHM Semiconductor.
+ * https://fscdn.rohm.com/en/products/databook/datasheet/ic/sensor/light/bu27034nuc-e.pdf
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/property.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/units.h>
+
+#include <linux/iio/buffer.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/iio-gts-helper.h>
+#include <linux/iio/kfifo_buf.h>
+
+#define BU27034_REG_SYSTEM_CONTROL	0x40
+#define BU27034_MASK_SW_RESET		BIT(7)
+#define BU27034_MASK_PART_ID		GENMASK(5, 0)
+#define BU27034_ID			0x19
+#define BU27034_REG_MODE_CONTROL1	0x41
+#define BU27034_MASK_MEAS_MODE		GENMASK(2, 0)
+
+#define BU27034_REG_MODE_CONTROL2	0x42
+#define BU27034_MASK_D01_GAIN		GENMASK(7, 3)
+#define BU27034_MASK_D2_GAIN_HI		GENMASK(7, 6)
+#define BU27034_MASK_D2_GAIN_LO		GENMASK(2, 0)
+
+#define BU27034_REG_MODE_CONTROL3	0x43
+#define BU27034_REG_MODE_CONTROL4	0x44
+#define BU27034_MASK_MEAS_EN		BIT(0)
+#define BU27034_MASK_VALID		BIT(7)
+#define BU27034_REG_DATA0_LO		0x50
+#define BU27034_REG_DATA1_LO		0x52
+#define BU27034_REG_DATA2_LO		0x54
+#define BU27034_REG_DATA2_HI		0x55
+#define BU27034_REG_MANUFACTURER_ID	0x92
+#define BU27034_REG_MAX BU27034_REG_MANUFACTURER_ID
+
+/*
+ * The BU27034 does not have interrupt to trigger the data read when a
+ * measurement has finished. Hence we poll the VALID bit in a thread. We will
+ * try to wake the thread BU27034_MEAS_WAIT_PREMATURE_MS milliseconds before
+ * the expected sampling time to prevent the drifting.
+ *
+ * If we constantly wake up a bit too late we would eventually skip a sample.
+ * And because the sleep can't wake up _exactly_ at given time this would be
+ * inevitable even if the sensor clock would be perfectly phase-locked to CPU
+ * clock - which we can't say is the case.
+ *
+ * This is still fragile. No matter how big advance do we have, we will still
+ * risk of losing a sample because things can in a rainy-day scenario be
+ * delayed a lot. Yet, more we reserve the time for polling, more we also lose
+ * the performance by spending cycles polling the register. So, selecting this
+ * value is a balancing dance between severity of wasting CPU time and severity
+ * of losing samples.
+ *
+ * In most cases losing the samples is not _that_ crucial because light levels
+ * tend to change slowly.
+ *
+ * Other option that was pointed to me would be always sleeping 1/2 of the
+ * measurement time, checking the VALID bit and just sleeping again if the bit
+ * was not set. That should be pretty tolerant against missing samples due to
+ * the scheduling delays while also not wasting much of cycles for polling.
+ * Downside is that the time-stamps would be very inaccurate as the wake-up
+ * would not really be tied to the sensor toggling the valid bit. This would also
+ * result 'jumps' in the time-stamps when the delay drifted so that wake-up was
+ * performed during the consecutive wake-ups (Or, when sensor and CPU clocks
+ * were very different and scheduling the wake-ups was very close to given
+ * timeout - and when the time-outs were very close to the actual sensor
+ * sampling, Eg. once in a blue moon, two consecutive time-outs would occur
+ * without having a sample ready).
+ */
+#define BU27034_MEAS_WAIT_PREMATURE_MS	5
+#define BU27034_DATA_WAIT_TIME_US	1000
+#define BU27034_TOTAL_DATA_WAIT_TIME_US (BU27034_MEAS_WAIT_PREMATURE_MS * 1000)
+
+#define BU27034_RETRY_LIMIT 18
+
+enum {
+	BU27034_CHAN_ALS,
+	BU27034_CHAN_DATA0,
+	BU27034_CHAN_DATA1,
+	BU27034_CHAN_DATA2,
+	BU27034_NUM_CHANS
+};
+
+static const unsigned long bu27034_scan_masks[] = {
+	GENMASK(BU27034_CHAN_DATA2, BU27034_CHAN_ALS), 0
+};
+
+/*
+ * Available scales with gain 1x - 4096x, timings 55, 100, 200, 400 mS
+ * Time impacts to gain: 1x, 2x, 4x, 8x.
+ *
+ * => Max total gain is HWGAIN * gain by integration time (8 * 4096) = 32768
+ *
+ * Using NANO precision for scale we must use scale 64x corresponding gain 1x
+ * to avoid precision loss. (32x would result scale 976 562.5(nanos).
+ */
+#define BU27034_SCALE_1X	64
+
+/* See the data sheet for the "Gain Setting" table */
+#define BU27034_GSEL_1X		0x00 /* 00000 */
+#define BU27034_GSEL_4X		0x08 /* 01000 */
+#define BU27034_GSEL_16X	0x0a /* 01010 */
+#define BU27034_GSEL_32X	0x0b /* 01011 */
+#define BU27034_GSEL_64X	0x0c /* 01100 */
+#define BU27034_GSEL_256X	0x18 /* 11000 */
+#define BU27034_GSEL_512X	0x19 /* 11001 */
+#define BU27034_GSEL_1024X	0x1a /* 11010 */
+#define BU27034_GSEL_2048X	0x1b /* 11011 */
+#define BU27034_GSEL_4096X	0x1c /* 11100 */
+
+/* Available gain settings */
+static const struct iio_gain_sel_pair bu27034_gains[] = {
+	GAIN_SCALE_GAIN(1, BU27034_GSEL_1X),
+	GAIN_SCALE_GAIN(4, BU27034_GSEL_4X),
+	GAIN_SCALE_GAIN(16, BU27034_GSEL_16X),
+	GAIN_SCALE_GAIN(32, BU27034_GSEL_32X),
+	GAIN_SCALE_GAIN(64, BU27034_GSEL_64X),
+	GAIN_SCALE_GAIN(256, BU27034_GSEL_256X),
+	GAIN_SCALE_GAIN(512, BU27034_GSEL_512X),
+	GAIN_SCALE_GAIN(1024, BU27034_GSEL_1024X),
+	GAIN_SCALE_GAIN(2048, BU27034_GSEL_2048X),
+	GAIN_SCALE_GAIN(4096, BU27034_GSEL_4096X),
+};
+
+/*
+ * The IC has 5 modes for sampling time. 5 mS mode is exceptional as it limits
+ * the data collection to data0-channel only and cuts the supported range to
+ * 10 bit. It is not supported by the driver.
+ *
+ * "normal" modes are 55, 100, 200 and 400 mS modes - which do have direct
+ * multiplying impact to the register values (similar to gain).
+ *
+ * This means that if meas-mode is changed for example from 400 => 200,
+ * the scale is doubled. Eg, time impact to total gain is x1, x2, x4, x8.
+ */
+#define BU27034_MEAS_MODE_100MS		0
+#define BU27034_MEAS_MODE_55MS		1
+#define BU27034_MEAS_MODE_200MS		2
+#define BU27034_MEAS_MODE_400MS		4
+
+static const struct iio_itime_sel_mul bu27034_itimes[] = {
+	GAIN_SCALE_ITIME_US(400000, BU27034_MEAS_MODE_400MS, 8),
+	GAIN_SCALE_ITIME_US(200000, BU27034_MEAS_MODE_200MS, 4),
+	GAIN_SCALE_ITIME_US(100000, BU27034_MEAS_MODE_100MS, 2),
+	GAIN_SCALE_ITIME_US(55000, BU27034_MEAS_MODE_55MS, 1),
+};
+
+#define BU27034_CHAN_DATA(_name, _ch2)					\
+{									\
+	.type = IIO_INTENSITY,						\
+	.channel = BU27034_CHAN_##_name,				\
+	.channel2 = (_ch2),						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |			\
+			      BIT(IIO_CHAN_INFO_SCALE),			\
+	.info_mask_separate_available = BIT(IIO_CHAN_INFO_SCALE),	\
+	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_INT_TIME),		\
+	.info_mask_shared_by_all_available =				\
+					BIT(IIO_CHAN_INFO_INT_TIME),	\
+	.address = BU27034_REG_##_name##_LO,				\
+	.scan_index = BU27034_CHAN_##_name,				\
+	.scan_type = {							\
+		.sign = 'u',						\
+		.realbits = 16,						\
+		.storagebits = 16,					\
+		.endianness = IIO_LE,					\
+	},								\
+	.indexed = 1,							\
+}
+
+static const struct iio_chan_spec bu27034_channels[] = {
+	{
+		.type = IIO_LIGHT,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				      BIT(IIO_CHAN_INFO_SCALE),
+		.channel = BU27034_CHAN_ALS,
+		.scan_index = BU27034_CHAN_ALS,
+		.scan_type = {
+			.sign = 'u',
+			.realbits = 32,
+			.storagebits = 32,
+			.endianness = IIO_CPU,
+		},
+	},
+	/*
+	 * The BU27034 DATA0 and DATA1 channels are both on the visible light
+	 * area (mostly). The data0 sensitivity peaks at 500nm, DATA1 at 600nm.
+	 * These wave lengths are pretty much on the border of colours making
+	 * these a poor candidates for R/G/B standardization. Hence they're both
+	 * marked as clear channels
+	 */
+	BU27034_CHAN_DATA(DATA0, IIO_MOD_LIGHT_CLEAR),
+	BU27034_CHAN_DATA(DATA1, IIO_MOD_LIGHT_CLEAR),
+	BU27034_CHAN_DATA(DATA2, IIO_MOD_LIGHT_IR),
+	IIO_CHAN_SOFT_TIMESTAMP(4),
+};
+
+struct bu27034_data {
+	struct regmap *regmap;
+	struct device *dev;
+	/*
+	 * Protect gain and time during scale adjustment and data reading.
+	 * Protect measurement enabling/disabling.
+	 */
+	struct mutex mutex;
+	struct iio_gts gts;
+	struct task_struct *task;
+	__le16 raw[3];
+	struct {
+		u32 mlux;
+		__le16 channels[3];
+		s64 ts __aligned(8);
+	} scan;
+};
+
+struct bu27034_result {
+	u16 ch0;
+	u16 ch1;
+	u16 ch2;
+};
+
+static const struct regmap_range bu27034_volatile_ranges[] = {
+	{
+		.range_min = BU27034_REG_SYSTEM_CONTROL,
+		.range_max = BU27034_REG_SYSTEM_CONTROL,
+	}, {
+		.range_min = BU27034_REG_MODE_CONTROL4,
+		.range_max = BU27034_REG_MODE_CONTROL4,
+	}, {
+		.range_min = BU27034_REG_DATA0_LO,
+		.range_max = BU27034_REG_DATA2_HI,
+	},
+};
+
+static const struct regmap_access_table bu27034_volatile_regs = {
+	.yes_ranges = &bu27034_volatile_ranges[0],
+	.n_yes_ranges = ARRAY_SIZE(bu27034_volatile_ranges),
+};
+
+static const struct regmap_range bu27034_read_only_ranges[] = {
+	{
+		.range_min = BU27034_REG_DATA0_LO,
+		.range_max = BU27034_REG_DATA2_HI,
+	}, {
+		.range_min = BU27034_REG_MANUFACTURER_ID,
+		.range_max = BU27034_REG_MANUFACTURER_ID,
+	}
+};
+
+static const struct regmap_access_table bu27034_ro_regs = {
+	.no_ranges = &bu27034_read_only_ranges[0],
+	.n_no_ranges = ARRAY_SIZE(bu27034_read_only_ranges),
+};
+
+static const struct regmap_config bu27034_regmap = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = BU27034_REG_MAX,
+	.cache_type = REGCACHE_RBTREE,
+	.volatile_table = &bu27034_volatile_regs,
+	.wr_table = &bu27034_ro_regs,
+};
+
+struct bu27034_gain_check {
+	int old_gain;
+	int new_gain;
+	int chan;
+};
+
+static int bu27034_get_gain_sel(struct bu27034_data *data, int chan)
+{
+	int ret, val;
+
+	switch (chan) {
+	case BU27034_CHAN_DATA0:
+	case BU27034_CHAN_DATA1:
+	{
+		int reg[] = {
+			[BU27034_CHAN_DATA0] = BU27034_REG_MODE_CONTROL2,
+			[BU27034_CHAN_DATA1] = BU27034_REG_MODE_CONTROL3,
+		};
+		ret = regmap_read(data->regmap, reg[chan], &val);
+		if (ret)
+			return ret;
+
+		return FIELD_GET(BU27034_MASK_D01_GAIN, val);
+	}
+	case BU27034_CHAN_DATA2:
+	{
+		int d2_lo_bits = fls(BU27034_MASK_D2_GAIN_LO);
+
+		ret = regmap_read(data->regmap, BU27034_REG_MODE_CONTROL2, &val);
+		if (ret)
+			return ret;
+
+		/*
+		 * The data2 channel gain is composed by 5 non continuous bits
+		 * [7:6], [2:0]. Thus when we combine the 5-bit 'selector'
+		 * from register value we must right shift the high bits by 3.
+		 */
+		return FIELD_GET(BU27034_MASK_D2_GAIN_HI, val) << d2_lo_bits |
+		       FIELD_GET(BU27034_MASK_D2_GAIN_LO, val);
+	}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int bu27034_get_gain(struct bu27034_data *data, int chan, int *gain)
+{
+	int ret, sel;
+
+	ret = bu27034_get_gain_sel(data, chan);
+	if (ret < 0)
+		return ret;
+
+	sel = ret;
+
+	ret = iio_gts_find_gain_by_sel(&data->gts, sel);
+	if (ret < 0) {
+		dev_err(data->dev, "chan %u: unknown gain value 0x%x\n", chan,
+			sel);
+
+		return ret;
+	}
+
+	*gain = ret;
+
+	return 0;
+}
+
+static int bu27034_get_int_time(struct bu27034_data *data)
+{
+	int ret, sel;
+
+	ret = regmap_read(data->regmap, BU27034_REG_MODE_CONTROL1, &sel);
+	if (ret)
+		return ret;
+
+	return iio_gts_find_int_time_by_sel(&data->gts,
+					    sel & BU27034_MASK_MEAS_MODE);
+}
+
+static int _bu27034_get_scale(struct bu27034_data *data, int channel, int *val,
+			      int *val2)
+{
+	int gain, ret;
+
+	ret = bu27034_get_gain(data, channel, &gain);
+	if (ret)
+		return ret;
+
+	ret = bu27034_get_int_time(data);
+	if (ret < 0)
+		return ret;
+
+	return iio_gts_get_scale(&data->gts, gain, ret, val, val2);
+}
+
+static int bu27034_get_scale(struct bu27034_data *data, int channel, int *val,
+			      int *val2)
+{
+	int ret;
+
+	if (channel == BU27034_CHAN_ALS) {
+		*val = 0;
+		*val2 = 1000;
+		return IIO_VAL_INT_PLUS_MICRO;
+	}
+
+	mutex_lock(&data->mutex);
+	ret = _bu27034_get_scale(data, channel, val, val2);
+	mutex_unlock(&data->mutex);
+	if (ret)
+		return ret;
+
+	return IIO_VAL_INT_PLUS_NANO;
+}
+
+/* Caller should hold the lock to protect lux reading */
+static int bu27034_write_gain_sel(struct bu27034_data *data, int chan, int sel)
+{
+	static const int reg[] = {
+		[BU27034_CHAN_DATA0] = BU27034_REG_MODE_CONTROL2,
+		[BU27034_CHAN_DATA1] = BU27034_REG_MODE_CONTROL3,
+	};
+	int mask, val;
+
+	if (chan != BU27034_CHAN_DATA0 && chan != BU27034_CHAN_DATA1)
+		return -EINVAL;
+
+	val = FIELD_PREP(BU27034_MASK_D01_GAIN, sel);
+
+	mask = BU27034_MASK_D01_GAIN;
+
+	if (chan == BU27034_CHAN_DATA0) {
+		/*
+		 * We keep the same gain for channel 2 as we set for channel 0
+		 * We can't allow them to be individually controlled because
+		 * setting one will impact also the other. Also, if we don't
+		 * always update both gains we may result unsupported bit
+		 * combinations.
+		 *
+		 * This is not nice but this is yet another place where the
+		 * user space must be prepared to surprizes. Namely, see chan 2
+		 * gain changed when chan 0 gain is changed.
+		 *
+		 * This is not fatal for most users though. I don't expect the
+		 * channel 2 to be used in any generic cases - the intensity
+		 * values provided by the sensor for IR area are not openly
+		 * documented. Also, channel 2 is not used for visible light.
+		 *
+		 * So, if there is application which is written to utilize the
+		 * channel 2 - then it is probably specifically targeted to this
+		 * sensor and knows how to utilize those values. It is safe to
+		 * hope such user can also cope with the gain changes.
+		 */
+		mask |=  BU27034_MASK_D2_GAIN_LO;
+
+		/*
+		 * The D2 gain bits are directly the lowest bits of selector.
+		 * Just do add those bits to the value
+		 */
+		val |= sel & BU27034_MASK_D2_GAIN_LO;
+	}
+
+	return regmap_update_bits(data->regmap, reg[chan], mask, val);
+}
+
+static int bu27034_set_gain(struct bu27034_data *data, int chan, int gain)
+{
+	int ret;
+
+	/*
+	 * We don't allow setting channel 2 gain as it messes up the
+	 * gain for channel 0 - which shares the high bits
+	 */
+	if (chan != BU27034_CHAN_DATA0 && chan != BU27034_CHAN_DATA1)
+		return -EINVAL;
+
+	ret = iio_gts_find_sel_by_gain(&data->gts, gain);
+	if (ret < 0)
+		return ret;
+
+	return bu27034_write_gain_sel(data, chan, ret);
+}
+
+/* Caller should hold the lock to protect data->int_time */
+static int bu27034_set_int_time(struct bu27034_data *data, int time)
+{
+	int ret;
+
+	ret = iio_gts_find_sel_by_int_time(&data->gts, time);
+	if (ret < 0)
+		return ret;
+
+	return regmap_update_bits(data->regmap, BU27034_REG_MODE_CONTROL1,
+				 BU27034_MASK_MEAS_MODE, ret);
+}
+
+/*
+ * We try to change the time in such way that the scale is maintained for
+ * given channels by adjusting gain so that it compensates the time change.
+ */
+static int bu27034_try_set_int_time(struct bu27034_data *data, int time_us)
+{
+	struct bu27034_gain_check gains[] = {
+		{ .chan = BU27034_CHAN_DATA0 },
+		{ .chan = BU27034_CHAN_DATA1 },
+	};
+	int numg = ARRAY_SIZE(gains);
+	int ret, int_time_old, i;
+
+	mutex_lock(&data->mutex);
+	ret = bu27034_get_int_time(data);
+	if (ret < 0)
+		goto unlock_out;
+
+	int_time_old = ret;
+
+	if (!iio_gts_valid_time(&data->gts, time_us)) {
+		dev_err(data->dev, "Unsupported integration time %u\n",
+			time_us);
+		ret = -EINVAL;
+
+		goto unlock_out;
+	}
+
+	if (time_us == int_time_old) {
+		ret = 0;
+		goto unlock_out;
+	}
+
+	for (i = 0; i < numg; i++) {
+		ret = bu27034_get_gain(data, gains[i].chan, &gains[i].old_gain);
+		if (ret)
+			goto unlock_out;
+
+		ret = iio_gts_find_new_gain_by_old_gain_time(&data->gts,
+							     gains[i].old_gain,
+							     int_time_old, time_us,
+							     &gains[i].new_gain);
+		if (ret) {
+			int scale1, scale2;
+			bool ok;
+
+			_bu27034_get_scale(data, gains[i].chan, &scale1, &scale2);
+			dev_dbg(data->dev,
+				"chan %u, can't support time %u with scale %u %u\n",
+				gains[i].chan, time_us, scale1, scale2);
+
+			if (gains[i].new_gain < 0)
+				goto unlock_out;
+
+			/*
+			 * If caller requests for integration time change and we
+			 * can't support the scale - then the caller should be
+			 * prepared to 'pick up the pieces and deal with the
+			 * fact that the scale changed'.
+			 */
+			ret = iio_find_closest_gain_low(&data->gts,
+							gains[i].new_gain, &ok);
+
+			if (!ok)
+				dev_dbg(data->dev,
+					"optimal gain out of range for chan %u\n",
+					gains[i].chan);
+
+			if (ret < 0) {
+				dev_dbg(data->dev,
+					 "Total gain increase. Risk of saturation");
+				ret = iio_gts_get_min_gain(&data->gts);
+				if (ret < 0)
+					goto unlock_out;
+			}
+			dev_dbg(data->dev, "chan %u scale changed\n",
+				 gains[i].chan);
+			gains[i].new_gain = ret;
+			dev_dbg(data->dev, "chan %u new gain %u\n",
+				gains[i].chan, gains[i].new_gain);
+		}
+	}
+
+	for (i = 0; i < numg; i++) {
+		ret = bu27034_set_gain(data, gains[i].chan, gains[i].new_gain);
+		if (ret)
+			goto unlock_out;
+	}
+
+	ret = bu27034_set_int_time(data, time_us);
+
+unlock_out:
+	mutex_unlock(&data->mutex);
+
+	return ret;
+}
+
+static int bu27034_set_scale(struct bu27034_data *data, int chan,
+			    int val, int val2)
+{
+	int ret, time_sel, gain_sel, i;
+	bool found = false;
+
+	if (chan == BU27034_CHAN_DATA2)
+		return -EINVAL;
+
+	if (chan == BU27034_CHAN_ALS) {
+		if (val == 0 && val2 == 1000000)
+			return 0;
+
+		return -EINVAL;
+	}
+
+	mutex_lock(&data->mutex);
+	ret = regmap_read(data->regmap, BU27034_REG_MODE_CONTROL1, &time_sel);
+	if (ret)
+		goto unlock_out;
+
+	ret = iio_gts_find_gain_sel_for_scale_using_time(&data->gts, time_sel,
+						val, val2, &gain_sel);
+	if (ret) {
+		/*
+		 * Could not support scale with given time. Need to change time.
+		 * We still want to maintain the scale for all channels
+		 */
+		struct bu27034_gain_check gain;
+		int new_time_sel;
+
+		/*
+		 * Populate information for the other channel which should also
+		 * maintain the scale. (Due to the HW limitations the chan2
+		 * gets the same gain as chan0, so we only need to explicitly
+		 * set the chan 0 and 1).
+		 */
+		if (chan == BU27034_CHAN_DATA0)
+			gain.chan = BU27034_CHAN_DATA1;
+		else if (chan == BU27034_CHAN_DATA1)
+			gain.chan = BU27034_CHAN_DATA0;
+
+		ret = bu27034_get_gain(data, gain.chan, &gain.old_gain);
+		if (ret)
+			goto unlock_out;
+
+		/*
+		 * Iterate through all the times to see if we find one which
+		 * can support requested scale for requested channel, while
+		 * maintaining the scale for other channels
+		 */
+		for (i = 0; i < data->gts.num_itime; i++) {
+			new_time_sel = data->gts.itime_table[i].sel;
+
+			if (new_time_sel == time_sel)
+				continue;
+
+			/* Can we provide requested scale with this time? */
+			ret = iio_gts_find_gain_sel_for_scale_using_time(
+				&data->gts, new_time_sel, val, val2,
+				&gain_sel);
+			if (ret)
+				continue;
+
+			/* Can the other channel(s) maintain scale? */
+			ret = iio_gts_find_new_gain_sel_by_old_gain_time(
+				&data->gts, gain.old_gain, time_sel,
+				new_time_sel, &gain.new_gain);
+			if (!ret) {
+				/* Yes - we found suitable time */
+				found = true;
+				break;
+			}
+		}
+		if (!found) {
+			dev_dbg(data->dev,
+				"Can't set scale maintaining other channels\n");
+			ret = -EINVAL;
+
+			goto unlock_out;
+		}
+
+		ret = bu27034_set_gain(data, gain.chan, gain.new_gain);
+		if (ret)
+			goto unlock_out;
+
+		ret = regmap_update_bits(data->regmap, BU27034_REG_MODE_CONTROL1,
+				  BU27034_MASK_MEAS_MODE, new_time_sel);
+		if (ret)
+			goto unlock_out;
+	}
+
+	ret = bu27034_write_gain_sel(data, chan, gain_sel);
+unlock_out:
+	mutex_unlock(&data->mutex);
+
+	return ret;
+}
+
+/*
+ * for (D1/D0 < 0.87):
+ * lx = 0.004521097 * D1 - 0.002663996 * D0 +
+ *	0.00012213 * D1 * D1 / D0
+ *
+ * =>	115.7400832 * ch1 / gain1 / mt -
+ *	68.1982976 * ch0 / gain0 / mt +
+ *	0.00012213 * 25600 * (ch1 / gain1 / mt) * 25600 *
+ *	(ch1 /gain1 / mt) / (25600 * ch0 / gain0 / mt)
+ *
+ * A =	0.00012213 * 25600 * (ch1 /gain1 / mt) * 25600 *
+ *	(ch1 /gain1 / mt) / (25600 * ch0 / gain0 / mt)
+ * =>	0.00012213 * 25600 * (ch1 /gain1 / mt) *
+ *	(ch1 /gain1 / mt) / (ch0 / gain0 / mt)
+ * =>	0.00012213 * 25600 * (ch1 / gain1) * (ch1 /gain1 / mt) /
+ *	(ch0 / gain0)
+ * =>	0.00012213 * 25600 * (ch1 / gain1) * (ch1 /gain1 / mt) *
+ *	gain0 / ch0
+ * =>	3.126528 * ch1 * ch1 * gain0 / gain1 / gain1 / mt /ch0
+ *
+ * lx = (115.7400832 * ch1 / gain1 - 68.1982976 * ch0 / gain0) /
+ *	mt + A
+ * =>	(115.7400832 * ch1 / gain1 - 68.1982976 * ch0 / gain0) /
+ *	mt + 3.126528 * ch1 * ch1 * gain0 / gain1 / gain1 / mt /
+ *	ch0
+ *
+ * =>	(115.7400832 * ch1 / gain1 - 68.1982976 * ch0 / gain0 +
+ *	  3.126528 * ch1 * ch1 * gain0 / gain1 / gain1 / ch0) /
+ *	  mt
+ *
+ * For (0.87 <= D1/D0 < 1.00)
+ * lx = (0.001331* D0 + 0.0000354 * D1) * ((D1/D0 – 0.87) * (0.385) + 1)
+ * =>	(0.001331 * 256 * 100 * ch0 / gain0 / mt + 0.0000354 * 256 *
+ *	100 * ch1 / gain1 / mt) * ((D1/D0 -  0.87) * (0.385) + 1)
+ * =>	(34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
+ *	((D1/D0 -  0.87) * (0.385) + 1)
+ * =>	(34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
+ *	(0.385 * D1/D0 - 0.66505)
+ * =>	(34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
+ *	(0.385 * 256 * 100 * ch1 / gain1 / mt / (256 * 100 * ch0 / gain0 / mt) - 0.66505)
+ * =>	(34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
+ *	(9856 * ch1 / gain1 / mt / (25600 * ch0 / gain0 / mt) + 0.66505)
+ * =>	13.118336 * ch1 / (gain1 * mt)
+ *	+ 22.66064768 * ch0 / (gain0 * mt)
+ *	+ 8931.90144 * ch1 * ch1 * gain0 /
+ *	  (25600 * ch0 * gain1 * gain1 * mt)
+ *	+ 0.602694912 * ch1 / (gain1 * mt)
+ *
+ * =>	[0.3489024 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1)
+ *	 + 22.66064768 * ch0 / gain0
+ *	 + 13.721030912 * ch1 / gain1
+ *	] / mt
+ *
+ * For (D1/D0 >= 1.00)
+ *
+ * lx	= (0.001331* D0 + 0.0000354 * D1) * ((D1/D0 – 2.0) * (-0.05) + 1)
+ *	=> (0.001331* D0 + 0.0000354 * D1) * (-0.05D1/D0 + 1.1)
+ *	=> (0.001331 * 256 * 100 * ch0 / gain0 / mt + 0.0000354 * 256 *
+ *	   100 * ch1 / gain1 / mt) * (-0.05D1/D0 + 1.1)
+ *	=> (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
+ *	   (-0.05 * 256 * 100 * ch1 / gain1 / mt / (256 * 100 * ch0 / gain0 / mt) + 1.1)
+ *	=> (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
+ *	   (-1280 * ch1 / (gain1 * mt * 25600 * ch0 / gain0 / mt) + 1.1)
+ *	=> (34.0736 * ch0 * -1280 * ch1 * gain0 * mt /( gain0 * mt * gain1 * mt * 25600 * ch0)
+ *	    + 34.0736 * 1.1 * ch0 / (gain0 * mt)
+ *	    + 0.90624 * ch1 * -1280 * ch1 *gain0 * mt / (gain1 * mt *gain1 * mt * 25600 * ch0)
+ *	    + 1.1 * 0.90624 * ch1 / (gain1 * mt)
+ *	=> -43614.208 * ch1 / (gain1 * mt * 25600)
+ *	    + 37.48096  ch0 / (gain0 * mt)
+ *	    - 1159.9872 * ch1 * ch1 * gain0 / (gain1 * gain1 * mt * 25600 * ch0)
+ *	    + 0.996864 ch1 / (gain1 * mt)
+ *	=> [
+ *		- 0.045312 * ch1 * ch1 * gain0 / (gain1 * gain1 * ch0)
+ *		- 0.706816 * ch1 / gain1
+ *		+ 37.48096  ch0 /gain0
+ *	   ] * mt
+ *
+ *
+ * So, the first case (D1/D0 < 0.87) can be computed to a form:
+ *
+ * lx = (3.126528 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1) +
+ *	 115.7400832 * ch1 / gain1 +
+ *	-68.1982976 * ch0 / gain0
+ *	 / mt
+ *
+ * Second case (0.87 <= D1/D0 < 1.00) goes to form:
+ *
+ *	=> [0.3489024 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1) +
+ *	    13.721030912 * ch1 / gain1 +
+ *	    22.66064768 * ch0 / gain0
+ *	   ] / mt
+ *
+ * Third case (D1/D0 >= 1.00) goes to form:
+ *	=> [-0.045312 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1) +
+ *	    -0.706816 * ch1 / gain1 +
+ *	    37.48096  ch0 /(gain0
+ *	   ] / mt
+ *
+ * This can be unified to format:
+ * lx = [
+ *	 A * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1) +
+ *	 B * ch1 / gain1 +
+ *	 C * ch0 / gain0
+ *	] / mt
+ *
+ * For case 1:
+ * A = 3.126528,
+ * B = 115.7400832
+ * C = -68.1982976
+ *
+ * For case 2:
+ * A = 0.3489024
+ * B = 13.721030912
+ * C = 22.66064768
+ *
+ * For case 3:
+ * A = -0.045312
+ * B = -0.706816
+ * C = 37.48096
+ */
+
+struct bu27034_lx_coeff {
+	unsigned int A;
+	unsigned int B;
+	unsigned int C;
+	/* Indicate which of the coefficients above are negative */
+	bool is_neg[3];
+};
+
+static inline u64 gain_mul_div_helper(u64 val, unsigned int gain,
+				      unsigned int div)
+{
+	/*
+	 * Max gain for a channel is 4096. The max u64 (0xffffffffffffffffULL)
+	 * divided by 4096 is 0xFFFFFFFFFFFFF (GENMASK_ULL(51, 0)) (floored).
+	 * Thus, the 0xFFFFFFFFFFFFF is the largest value we can safely multiply
+	 * with the gain, no matter what gain is set.
+	 *
+	 * So, multiplication with max gain may overflow if val is greater than
+	 * 0xFFFFFFFFFFFFF (52 bits set)..
+	 *
+	 * If this is the case we divide first.
+	 */
+	if (val < GENMASK_ULL(51, 0)) {
+		val *= gain;
+		do_div(val, div);
+	} else {
+		do_div(val, div);
+		val *= gain;
+	}
+
+	return val;
+}
+
+static u64 bu27034_fixp_calc_t1_64bit(unsigned int coeff, unsigned int ch0,
+				      unsigned int ch1, unsigned int gain0,
+				      unsigned int gain1)
+{
+	unsigned int helper;
+	u64 helper64;
+
+	helper64 = (u64)coeff * (u64)ch1 * (u64)ch1;
+
+	helper = gain1 * gain1;
+	if (helper > ch0) {
+		do_div(helper64, helper);
+
+		return gain_mul_div_helper(helper64, gain0, ch0);
+	}
+
+	do_div(helper64, ch0);
+
+	return gain_mul_div_helper(helper64, gain0, helper);
+
+}
+
+static u64 bu27034_fixp_calc_t1(unsigned int coeff, unsigned int ch0,
+				unsigned int ch1, unsigned int gain0,
+				unsigned int gain1)
+{
+	unsigned int helper, tmp;
+
+	/*
+	 * Here we could overflow even the 64bit value. Hence we
+	 * multiply with gain0 only after the divisions - even though
+	 * it may result loss of accuracy
+	 */
+	helper = coeff * ch1 * ch1;
+	tmp = helper * gain0;
+
+	helper = ch1 * ch1;
+
+	if (check_mul_overflow(helper, coeff, &helper))
+		return bu27034_fixp_calc_t1_64bit(coeff, ch0, ch1, gain0, gain1);
+
+	if (check_mul_overflow(helper, gain0, &tmp))
+		return bu27034_fixp_calc_t1_64bit(coeff, ch0, ch1, gain0, gain1);
+
+	return tmp / (gain1 * gain1) / ch0;
+
+}
+
+static u64 bu27034_fixp_calc_t23(unsigned int coeff, unsigned int ch,
+				 unsigned int gain)
+{
+	unsigned int helper;
+	u64 helper64;
+
+	if (!check_mul_overflow(coeff, ch, &helper))
+		return helper / gain;
+
+	helper64 = (u64)coeff * (u64)ch;
+	do_div(helper64, gain);
+
+	return helper64;
+}
+
+static int bu27034_fixp_calc_lx(unsigned int ch0, unsigned int ch1,
+				unsigned int gain0, unsigned int gain1,
+				unsigned int meastime, int coeff_idx)
+{
+	static const struct bu27034_lx_coeff coeff[] = {
+		{
+			.A = 31265280,		/* 3.126528 */
+			.B = 1157400832,	/*115.7400832 */
+			.C = 681982976,		/* -68.1982976 */
+			.is_neg = {false, false, true},
+		}, {
+			.A = 3489024,		/* 0.3489024 */
+			.B = 137210309,		/* 13.721030912 */
+			.C = 226606476,		/* 22.66064768 */
+			/* All terms positive */
+		}, {
+			.A = 453120,		/* -0.045312 */
+			.B = 7068160,		/* -0.706816 */
+			.C = 374809600,		/* 37.48096 */
+			.is_neg = {true, true, false},
+		}
+	};
+	const struct bu27034_lx_coeff *c = &coeff[coeff_idx];
+	u64 res = 0, terms[3];
+	int i;
+
+	if (coeff_idx >= ARRAY_SIZE(coeff))
+		return -EINVAL;
+
+	terms[0] = bu27034_fixp_calc_t1(c->A, ch0, ch1, gain0, gain1);
+	terms[1] = bu27034_fixp_calc_t23(c->B, ch1, gain1);
+	terms[2] = bu27034_fixp_calc_t23(c->C, ch0, gain0);
+
+	/* First, add positive terms */
+	for (i = 0; i < 3; i++)
+		if (!c->is_neg[i])
+			res += terms[i];
+
+	/* No positive term => zero lux */
+	if (!res)
+		return 0;
+
+	/* Then, subtract negative terms (if any) */
+	for (i = 0; i < 3; i++)
+		if (c->is_neg[i]) {
+			/*
+			 * If the negative term is greater than positive - then
+			 * the darkness has taken over and we are all doomed! Eh,
+			 * I mean, then we can just return 0 lx and go out
+			 */
+			if (terms[i] >= res)
+				return 0;
+
+			res -= terms[i];
+		}
+
+	meastime *= 10;
+	do_div(res, meastime);
+
+	return (int) res;
+}
+
+static bool bu27034_has_valid_sample(struct bu27034_data *data)
+{
+	int ret, val;
+
+	ret = regmap_read(data->regmap, BU27034_REG_MODE_CONTROL4, &val);
+	if (ret) {
+		dev_err(data->dev, "Read failed %d\n", ret);
+
+		return false;
+	}
+
+	return val & BU27034_MASK_VALID;
+}
+
+/*
+ * Reading the register where VALID bit is clears this bit. (So does changing
+ * any gain / integration time configuration registers) The bit gets
+ * set when we have acquired new data. We use this bit to indicate data
+ * validity.
+ */
+static void bu27034_invalidate_read_data(struct bu27034_data *data)
+{
+	bu27034_has_valid_sample(data);
+}
+
+static int bu27034_read_result(struct bu27034_data *data, int chan, int *res)
+{
+	int reg[] = {
+		[BU27034_CHAN_DATA0] = BU27034_REG_DATA0_LO,
+		[BU27034_CHAN_DATA1] = BU27034_REG_DATA1_LO,
+		[BU27034_CHAN_DATA2] = BU27034_REG_DATA2_LO,
+	};
+	int valid, ret;
+	__le16 val;
+
+	ret = regmap_read_poll_timeout(data->regmap, BU27034_REG_MODE_CONTROL4,
+				       valid, (valid & BU27034_MASK_VALID),
+				       BU27034_DATA_WAIT_TIME_US, 0);
+	if (ret)
+		return ret;
+
+	ret = regmap_bulk_read(data->regmap, reg[chan], &val, sizeof(val));
+	if (ret)
+		return ret;
+
+	*res = le16_to_cpu(val);
+
+	return 0;
+}
+
+static int bu27034_get_result_unlocked(struct bu27034_data *data, __le16 *res,
+				       int size)
+{
+	int ret = 0, retry_cnt = 0;
+
+retry:
+	/* Get new value from sensor if data is ready */
+	if (bu27034_has_valid_sample(data)) {
+		ret = regmap_bulk_read(data->regmap, BU27034_REG_DATA0_LO,
+				       res, size);
+		if (ret)
+			return ret;
+
+		bu27034_invalidate_read_data(data);
+	} else {
+		/* No new data in sensor. Wait and retry */
+		retry_cnt++;
+
+		if (retry_cnt > BU27034_RETRY_LIMIT) {
+			dev_err(data->dev, "No data from sensor\n");
+
+			return -ETIMEDOUT;
+		}
+
+		msleep(25);
+
+		goto retry;
+	}
+
+	return ret;
+}
+
+static int bu27034_meas_set(struct bu27034_data *data, bool en)
+{
+	if (en)
+		return regmap_set_bits(data->regmap, BU27034_REG_MODE_CONTROL4,
+				       BU27034_MASK_MEAS_EN);
+
+	return regmap_clear_bits(data->regmap, BU27034_REG_MODE_CONTROL4,
+				 BU27034_MASK_MEAS_EN);
+}
+
+static int bu27034_get_single_result(struct bu27034_data *data, int chan,
+				     int *val)
+{
+	int ret;
+
+	if (chan < BU27034_CHAN_DATA0 || chan > BU27034_CHAN_DATA2)
+		return -EINVAL;
+
+	ret = bu27034_meas_set(data, true);
+	if (ret)
+		return ret;
+
+	ret = bu27034_get_int_time(data);
+	if (ret < 0)
+		return ret;
+
+	msleep(ret / 1000);
+
+	return bu27034_read_result(data, chan, val);
+}
+
+/*
+ * The formula given by vendor for computing luxes out of data0 and data1
+ * (in open air) is as follows:
+ *
+ * Let's mark:
+ * D0 = data0/ch0_gain/meas_time_ms * 25600
+ * D1 = data1/ch1_gain/meas_time_ms * 25600
+ *
+ * Then:
+ * if (D1/D0 < 0.87)
+ *	lx = (0.001331 * D0 + 0.0000354 * D1) * ((D1 / D0 - 0.87) * 3.45 + 1)
+ * else if (D1/D0 < 1)
+ *	lx = (0.001331 * D0 + 0.0000354 * D1) * ((D1 / D0 - 0.87) * 0.385 + 1)
+ * else
+ *	lx = (0.001331 * D0 + 0.0000354 * D1) * ((D1 / D0 - 2) * -0.05 + 1)
+ *
+ * We use it here. Users who have for example some colored lens
+ * need to modify the calculation but I hope this gives a starting point for
+ * those working with such devices.
+ */
+
+static int bu27034_calc_mlux(struct bu27034_data *data, __le16 *res, int *val)
+{
+	unsigned int gain0, gain1, meastime;
+	unsigned int d1_d0_ratio_scaled;
+	u16 ch0, ch1;
+	u64 helper64;
+	int ret;
+
+	/*
+	 * We return 0 lux if calculation fails. This should be reasonably
+	 * easy to spot from the buffers especially if raw-data channels show
+	 * valid values
+	 */
+	*val = 0;
+
+	ch0 = max_t(u16, 1, le16_to_cpu(res[0]));
+	ch1 = max_t(u16, 1, le16_to_cpu(res[1]));
+
+	ret = bu27034_get_gain(data, BU27034_CHAN_DATA0, &gain0);
+	if (ret)
+		return ret;
+
+	ret = bu27034_get_gain(data, BU27034_CHAN_DATA1, &gain1);
+	if (ret)
+		return ret;
+
+	ret = bu27034_get_int_time(data);
+	if (ret < 0)
+		return ret;
+
+	meastime = ret;
+
+	d1_d0_ratio_scaled = (unsigned int)ch1 * (unsigned int)gain0 * 100;
+	helper64 = (u64)ch1 * (u64)gain0 * 100LLU;
+
+	if (helper64 != d1_d0_ratio_scaled) {
+		unsigned int div = (unsigned int)ch0 * gain1;
+
+		do_div(helper64, div);
+		d1_d0_ratio_scaled = helper64;
+	} else {
+		d1_d0_ratio_scaled /= ch0 * gain1;
+	}
+
+	if (d1_d0_ratio_scaled < 87)
+		ret = bu27034_fixp_calc_lx(ch0, ch1, gain0, gain1, meastime, 0);
+	else if (d1_d0_ratio_scaled < 100)
+		ret = bu27034_fixp_calc_lx(ch0, ch1, gain0, gain1, meastime, 1);
+	else
+		ret = bu27034_fixp_calc_lx(ch0, ch1, gain0, gain1, meastime, 2);
+
+	if (ret < 0)
+		return ret;
+
+	*val = ret;
+
+	return 0;
+
+}
+
+static int bu27034_get_mlux(struct bu27034_data *data, int chan, int *val)
+{
+	__le16 res[3];
+	int ret;
+
+	ret = bu27034_meas_set(data, true);
+	if (ret)
+		return ret;
+
+	ret = bu27034_get_result_unlocked(data, &res[0], sizeof(res));
+	if (ret)
+		return ret;
+
+	ret = bu27034_calc_mlux(data, res, val);
+	if (ret)
+		return ret;
+
+	ret = bu27034_meas_set(data, false);
+	if (ret)
+		dev_err(data->dev, "failed to disable measurement\n");
+
+	return 0;
+}
+
+static int bu27034_read_raw(struct iio_dev *idev,
+			   struct iio_chan_spec const *chan,
+			   int *val, int *val2, long mask)
+{
+	struct bu27034_data *data = iio_priv(idev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_INT_TIME:
+		*val = 0;
+		*val2 = bu27034_get_int_time(data);
+		if (*val2 < 0)
+			return *val2;
+
+		return IIO_VAL_INT_PLUS_MICRO;
+
+	case IIO_CHAN_INFO_SCALE:
+		return bu27034_get_scale(data, chan->channel, val, val2);
+
+	case IIO_CHAN_INFO_RAW:
+	{
+		int (*result_get)(struct bu27034_data *data, int chan, int *val);
+
+		if (chan->type == IIO_INTENSITY)
+			result_get = bu27034_get_single_result;
+		else if (chan->type == IIO_LIGHT)
+			result_get = bu27034_get_mlux;
+		else
+			return -EINVAL;
+
+		/* Don't mess with measurement enabling while buffering */
+		ret = iio_device_claim_direct_mode(idev);
+		if (ret)
+			return ret;
+
+		mutex_lock(&data->mutex);
+		/*
+		 * Reading one channel at a time is inefficient but we
+		 * don't care here. Buffered version should be used if
+		 * performance is an issue.
+		 */
+		ret = result_get(data, chan->channel, val);
+
+		mutex_unlock(&data->mutex);
+		iio_device_release_direct_mode(idev);
+
+		if (ret)
+			return ret;
+
+		return IIO_VAL_INT;
+	}
+	default:
+		return -EINVAL;
+	}
+}
+
+static int bu27034_write_raw_get_fmt(struct iio_dev *indio_dev,
+				     struct iio_chan_spec const *chan,
+				     long mask)
+{
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_INT_TIME:
+		return IIO_VAL_INT_PLUS_MICRO;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int bu27034_write_raw(struct iio_dev *idev,
+			     struct iio_chan_spec const *chan,
+			     int val, int val2, long mask)
+{
+	struct bu27034_data *data = iio_priv(idev);
+	int ret;
+
+	ret = iio_device_claim_direct_mode(idev);
+	if (ret)
+		return ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		ret = bu27034_set_scale(data, chan->channel, val, val2);
+		break;
+	case IIO_CHAN_INFO_INT_TIME:
+		if (!val)
+			ret = bu27034_try_set_int_time(data, val2);
+		else
+			ret = -EINVAL;
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	iio_device_release_direct_mode(idev);
+
+	return ret;
+}
+
+static int bu27034_read_avail(struct iio_dev *idev,
+			      struct iio_chan_spec const *chan, const int **vals,
+			      int *type, int *length, long mask)
+{
+	struct bu27034_data *data = iio_priv(idev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_INT_TIME:
+		return iio_gts_avail_times(&data->gts, vals, type, length);
+	case IIO_CHAN_INFO_SCALE:
+		return iio_gts_all_avail_scales(&data->gts, vals, type, length);
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info bu27034_info = {
+	.read_raw = &bu27034_read_raw,
+	.write_raw = &bu27034_write_raw,
+	.write_raw_get_fmt = &bu27034_write_raw_get_fmt,
+	.read_avail = &bu27034_read_avail,
+};
+
+static int bu27034_chip_init(struct bu27034_data *data)
+{
+	int ret, sel;
+
+	/* Reset */
+	ret = regmap_write_bits(data->regmap, BU27034_REG_SYSTEM_CONTROL,
+			   BU27034_MASK_SW_RESET, BU27034_MASK_SW_RESET);
+	if (ret)
+		return dev_err_probe(data->dev, ret, "Sensor reset failed\n");
+
+	msleep(1);
+
+	ret = regmap_reinit_cache(data->regmap, &bu27034_regmap);
+	if (ret) {
+		dev_err(data->dev, "Failed to reinit reg cache\n");
+		return ret;
+	}
+
+	/*
+	 * Read integration time here to ensure it is in regmap cache. We do
+	 * this to speed-up the int-time acquisition in the start of the buffer
+	 * handling thread where longer delays could make it more likely we end
+	 * up skipping a sample, and where the longer delays make timestamps
+	 * less accurate.
+	 */
+	ret = regmap_read(data->regmap, BU27034_REG_MODE_CONTROL1, &sel);
+	if (ret)
+		dev_err(data->dev, "reading integration time failed\n");
+
+	return 0;
+}
+
+static int bu27034_wait_for_data(struct bu27034_data *data)
+{
+	int ret, val;
+
+	ret = regmap_read_poll_timeout(data->regmap, BU27034_REG_MODE_CONTROL4,
+				       val, val & BU27034_MASK_VALID,
+				       BU27034_DATA_WAIT_TIME_US,
+				       BU27034_TOTAL_DATA_WAIT_TIME_US);
+	if (ret) {
+		dev_err(data->dev, "data polling %s\n",
+			!(val & BU27034_MASK_VALID) ? "timeout" : "fail");
+
+		return ret;
+	}
+
+	ret = regmap_bulk_read(data->regmap, BU27034_REG_DATA0_LO,
+			       &data->scan.channels[0],
+			       sizeof(data->scan.channels));
+	if (ret)
+		return ret;
+
+	bu27034_invalidate_read_data(data);
+
+	return 0;
+}
+
+static int bu27034_buffer_thread(void *arg)
+{
+	struct iio_dev *idev = arg;
+	struct bu27034_data *data;
+	int wait_ms;
+
+	data = iio_priv(idev);
+
+	wait_ms = bu27034_get_int_time(data);
+	wait_ms /= 1000;
+
+	wait_ms -= BU27034_MEAS_WAIT_PREMATURE_MS;
+
+	while (!kthread_should_stop()) {
+		int ret;
+		int64_t tstamp;
+
+		msleep(wait_ms);
+		ret = bu27034_wait_for_data(data);
+		if (ret)
+			continue;
+
+		tstamp = iio_get_time_ns(idev);
+
+		if (test_bit(BU27034_CHAN_ALS, idev->active_scan_mask)) {
+			int mlux;
+
+			ret = bu27034_calc_mlux(data, &data->scan.channels[0],
+					       &mlux);
+			if (ret)
+				dev_err(data->dev, "failed to calculate lux\n");
+
+			/*
+			 * The maximum Milli lux value we get with gain 1x time
+			 * 55mS data ch0 = 0xffff ch1 = 0xffff fits in 26 bits
+			 * so there should be no problem returning int from
+			 * computations and casting it to u32
+			 */
+			data->scan.mlux = (u32)mlux;
+		}
+		iio_push_to_buffers_with_timestamp(idev, &data->scan, tstamp);
+	}
+
+	return 0;
+}
+
+static int bu27034_buffer_enable(struct iio_dev *idev)
+{
+	struct bu27034_data *data = iio_priv(idev);
+	struct task_struct *task;
+	int ret;
+
+	mutex_lock(&data->mutex);
+	ret = bu27034_meas_set(data, true);
+	if (ret)
+		goto unlock_out;
+
+	task = kthread_run(bu27034_buffer_thread, idev,
+				 "bu27034-buffering-%u",
+				 iio_device_id(idev));
+	if (IS_ERR(task)) {
+		ret = PTR_ERR(task);
+		goto unlock_out;
+	}
+
+	data->task = task;
+
+unlock_out:
+	mutex_unlock(&data->mutex);
+
+	return ret;
+}
+
+static int bu27034_buffer_disable(struct iio_dev *idev)
+{
+	struct bu27034_data *data = iio_priv(idev);
+	int ret;
+
+	mutex_lock(&data->mutex);
+	if (data->task) {
+		kthread_stop(data->task);
+		data->task = NULL;
+	}
+
+	ret = bu27034_meas_set(data, false);
+	mutex_unlock(&data->mutex);
+
+	return ret;
+}
+
+static const struct iio_buffer_setup_ops bu27034_buffer_ops = {
+	.postenable = &bu27034_buffer_enable,
+	.predisable = &bu27034_buffer_disable,
+};
+
+static int bu27034_probe(struct i2c_client *i2c)
+{
+	struct device *dev = &i2c->dev;
+	struct bu27034_data *data;
+	struct regmap *regmap;
+	struct iio_dev *idev;
+	unsigned int part_id, reg;
+	int ret;
+
+	regmap = devm_regmap_init_i2c(i2c, &bu27034_regmap);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap),
+				     "Failed to initialize Regmap\n");
+
+	idev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!idev)
+		return -ENOMEM;
+
+	ret = devm_regulator_get_enable(dev, "vdd");
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to get regulator\n");
+
+	data = iio_priv(idev);
+
+	ret = regmap_read(regmap, BU27034_REG_SYSTEM_CONTROL, &reg);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to access sensor\n");
+
+	part_id = FIELD_GET(BU27034_MASK_PART_ID, reg);
+
+	if (part_id != BU27034_ID)
+		dev_warn(dev, "unknown device 0x%x\n", part_id);
+
+	ret = devm_iio_init_iio_gts(dev, BU27034_SCALE_1X, 0, bu27034_gains,
+				    ARRAY_SIZE(bu27034_gains), bu27034_itimes,
+				    ARRAY_SIZE(bu27034_itimes), &data->gts);
+	if (ret)
+		return ret;
+
+	mutex_init(&data->mutex);
+	data->regmap = regmap;
+	data->dev = dev;
+
+	idev->channels = bu27034_channels;
+	idev->num_channels = ARRAY_SIZE(bu27034_channels);
+	idev->name = "bu27034";
+	idev->info = &bu27034_info;
+
+	idev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_SOFTWARE;
+	idev->available_scan_masks = bu27034_scan_masks;
+
+	ret = bu27034_chip_init(data);
+	if (ret)
+		return ret;
+
+	ret = devm_iio_kfifo_buffer_setup(dev, idev, &bu27034_buffer_ops);
+	if (ret)
+		return dev_err_probe(dev, ret, "buffer setup failed\n");
+
+	ret = devm_iio_device_register(dev, idev);
+	if (ret < 0)
+		return dev_err_probe(dev, ret,
+				     "Unable to register iio device\n");
+
+	return ret;
+}
+
+static const struct of_device_id bu27034_of_match[] = {
+	{ .compatible = "rohm,bu27034" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, bu27034_of_match);
+
+static struct i2c_driver bu27034_i2c_driver = {
+	.driver = {
+		.name = "bu27034-als",
+		.of_match_table = bu27034_of_match,
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+	},
+	.probe = bu27034_probe,
+};
+module_i2c_driver(bu27034_i2c_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>");
+MODULE_DESCRIPTION("ROHM BU27034 ambient light sensor driver");
+MODULE_IMPORT_NS(IIO_GTS_HELPER);