iio: dac: add support for ltc2688

The LTC2688 is a 16 channel, 16 bit, +-15V DAC with an integrated
precision reference. It is guaranteed monotonic and has built in
rail-to-rail output buffers that can source or sink up to 20 mA.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20220225130129.69-2-nuno.sa@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

3 files changed, 1083 insertions, 0 deletions

diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
index bfcf7568de32..c0bf0d84197f 100644
--- a/drivers/iio/dac/Kconfig
+++ b/drivers/iio/dac/Kconfig
@@ -131,6 +131,17 @@ config AD5624R_SPI
 	  Say yes here to build support for Analog Devices AD5624R, AD5644R and
 	  AD5664R converters (DAC). This driver uses the common SPI interface.
 
+config LTC2688
+	tristate "Analog Devices LTC2688 DAC spi driver"
+	depends on SPI
+	select REGMAP
+	help
+	  Say yes here to build support for Analog Devices
+	  LTC2688 converters (DAC).
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ltc2688.
+
 config AD5686
 	tristate
 
diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
index 01a50131572f..ec3e42713f00 100644
--- a/drivers/iio/dac/Makefile
+++ b/drivers/iio/dac/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_DS4424) += ds4424.o
 obj-$(CONFIG_LPC18XX_DAC) += lpc18xx_dac.o
 obj-$(CONFIG_LTC1660) += ltc1660.o
 obj-$(CONFIG_LTC2632) += ltc2632.o
+obj-$(CONFIG_LTC2688) += ltc2688.o
 obj-$(CONFIG_M62332) += m62332.o
 obj-$(CONFIG_MAX517) += max517.o
 obj-$(CONFIG_MAX5821) += max5821.o
diff --git a/drivers/iio/dac/ltc2688.c b/drivers/iio/dac/ltc2688.c
new file mode 100644
index 000000000000..e41861d29767
--- /dev/null
+++ b/drivers/iio/dac/ltc2688.c
@@ -0,0 +1,1071 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * LTC2688 16 channel, 16 bit Voltage Output SoftSpan DAC driver
+ *
+ * Copyright 2022 Analog Devices Inc.
+ */
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/clk.h>
+#include <linux/device.h>
+#include <linux/gpio/consumer.h>
+#include <linux/iio/iio.h>
+#include <linux/limits.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/property.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+
+#define LTC2688_DAC_CHANNELS			16
+
+#define LTC2688_CMD_CH_CODE(x)			(0x00 + (x))
+#define LTC2688_CMD_CH_SETTING(x)		(0x10 + (x))
+#define LTC2688_CMD_CH_OFFSET(x)		(0X20 + (x))
+#define LTC2688_CMD_CH_GAIN(x)			(0x30 + (x))
+#define LTC2688_CMD_CH_CODE_UPDATE(x)		(0x40 + (x))
+
+#define LTC2688_CMD_CONFIG			0x70
+#define LTC2688_CMD_POWERDOWN			0x71
+#define LTC2688_CMD_A_B_SELECT			0x72
+#define LTC2688_CMD_SW_TOGGLE			0x73
+#define LTC2688_CMD_TOGGLE_DITHER_EN		0x74
+#define LTC2688_CMD_THERMAL_STAT		0x77
+#define LTC2688_CMD_UPDATE_ALL			0x7C
+#define LTC2688_CMD_NOOP			0xFF
+
+#define LTC2688_READ_OPERATION			0x80
+
+/* Channel Settings */
+#define LTC2688_CH_SPAN_MSK			GENMASK(2, 0)
+#define LTC2688_CH_OVERRANGE_MSK		BIT(3)
+#define LTC2688_CH_TD_SEL_MSK			GENMASK(5, 4)
+#define LTC2688_CH_TGP_MAX			3
+#define LTC2688_CH_DIT_PER_MSK			GENMASK(8, 6)
+#define LTC2688_CH_DIT_PH_MSK			GENMASK(10, 9)
+#define LTC2688_CH_MODE_MSK			BIT(11)
+
+#define LTC2688_DITHER_RAW_MASK			GENMASK(15, 2)
+#define LTC2688_CH_CALIBBIAS_MASK		GENMASK(15, 2)
+#define LTC2688_DITHER_RAW_MAX_VAL		(BIT(14) - 1)
+#define LTC2688_CH_CALIBBIAS_MAX_VAL		(BIT(14) - 1)
+
+/* Configuration register */
+#define LTC2688_CONFIG_RST			BIT(15)
+#define LTC2688_CONFIG_EXT_REF			BIT(1)
+
+#define LTC2688_DITHER_FREQ_AVAIL_N		5
+
+enum {
+	LTC2688_SPAN_RANGE_0V_5V,
+	LTC2688_SPAN_RANGE_0V_10V,
+	LTC2688_SPAN_RANGE_M5V_5V,
+	LTC2688_SPAN_RANGE_M10V_10V,
+	LTC2688_SPAN_RANGE_M15V_15V,
+	LTC2688_SPAN_RANGE_MAX
+};
+
+enum {
+	LTC2688_MODE_DEFAULT,
+	LTC2688_MODE_DITHER_TOGGLE,
+};
+
+struct ltc2688_chan {
+	long dither_frequency[LTC2688_DITHER_FREQ_AVAIL_N];
+	bool overrange;
+	bool toggle_chan;
+	u8 mode;
+};
+
+struct ltc2688_state {
+	struct spi_device *spi;
+	struct regmap *regmap;
+	struct regulator_bulk_data regulators[2];
+	struct ltc2688_chan channels[LTC2688_DAC_CHANNELS];
+	struct iio_chan_spec *iio_chan;
+	/* lock to protect against multiple access to the device and shared data */
+	struct mutex lock;
+	int vref;
+	/*
+	 * DMA (thus cache coherency maintenance) requires the
+	 * transfer buffers to live in their own cache lines.
+	 */
+	u8 tx_data[6] ____cacheline_aligned;
+	u8 rx_data[3];
+};
+
+static int ltc2688_spi_read(void *context, const void *reg, size_t reg_size,
+			    void *val, size_t val_size)
+{
+	struct ltc2688_state *st = context;
+	struct spi_transfer xfers[] = {
+		{
+			.tx_buf = st->tx_data,
+			.bits_per_word = 8,
+			.len = reg_size + val_size,
+			.cs_change = 1,
+		}, {
+			.tx_buf = st->tx_data + 3,
+			.rx_buf = st->rx_data,
+			.bits_per_word = 8,
+			.len = reg_size + val_size,
+		},
+	};
+	int ret;
+
+	memcpy(st->tx_data, reg, reg_size);
+
+	ret = spi_sync_transfer(st->spi, xfers, ARRAY_SIZE(xfers));
+	if (ret)
+		return ret;
+
+	memcpy(val, &st->rx_data[1], val_size);
+
+	return 0;
+}
+
+static int ltc2688_spi_write(void *context, const void *data, size_t count)
+{
+	struct ltc2688_state *st = context;
+
+	return spi_write(st->spi, data, count);
+}
+
+static int ltc2688_span_get(const struct ltc2688_state *st, int c)
+{
+	int ret, reg, span;
+
+	ret = regmap_read(st->regmap, LTC2688_CMD_CH_SETTING(c), &reg);
+	if (ret)
+		return ret;
+
+	span = FIELD_GET(LTC2688_CH_SPAN_MSK, reg);
+	/* sanity check to make sure we don't get any weird value from the HW */
+	if (span >= LTC2688_SPAN_RANGE_MAX)
+		return -EIO;
+
+	return span;
+}
+
+static const int ltc2688_span_helper[LTC2688_SPAN_RANGE_MAX][2] = {
+	{0, 5000}, {0, 10000}, {-5000, 5000}, {-10000, 10000}, {-15000, 15000},
+};
+
+static int ltc2688_scale_get(const struct ltc2688_state *st, int c, int *val)
+{
+	const struct ltc2688_chan *chan = &st->channels[c];
+	int span, fs;
+
+	span = ltc2688_span_get(st, c);
+	if (span < 0)
+		return span;
+
+	fs = ltc2688_span_helper[span][1] - ltc2688_span_helper[span][0];
+	if (chan->overrange)
+		fs = mult_frac(fs, 105, 100);
+
+	*val = DIV_ROUND_CLOSEST(fs * st->vref, 4096);
+
+	return 0;
+}
+
+static int ltc2688_offset_get(const struct ltc2688_state *st, int c, int *val)
+{
+	int span;
+
+	span = ltc2688_span_get(st, c);
+	if (span < 0)
+		return span;
+
+	if (ltc2688_span_helper[span][0] < 0)
+		*val = -32768;
+	else
+		*val = 0;
+
+	return 0;
+}
+
+enum {
+	LTC2688_INPUT_A,
+	LTC2688_INPUT_B,
+	LTC2688_INPUT_B_AVAIL,
+	LTC2688_DITHER_OFF,
+	LTC2688_DITHER_FREQ_AVAIL,
+};
+
+static int ltc2688_dac_code_write(struct ltc2688_state *st, u32 chan, u32 input,
+				  u16 code)
+{
+	struct ltc2688_chan *c = &st->channels[chan];
+	int ret, reg;
+
+	/* 2 LSBs set to 0 if writing dither amplitude */
+	if (!c->toggle_chan && input == LTC2688_INPUT_B) {
+		if (code > LTC2688_DITHER_RAW_MAX_VAL)
+			return -EINVAL;
+
+		code = FIELD_PREP(LTC2688_DITHER_RAW_MASK, code);
+	}
+
+	mutex_lock(&st->lock);
+	/* select the correct input register to read from */
+	ret = regmap_update_bits(st->regmap, LTC2688_CMD_A_B_SELECT, BIT(chan),
+				 input << chan);
+	if (ret)
+		goto out_unlock;
+
+	/*
+	 * If in dither/toggle mode the dac should be updated by an
+	 * external signal (or sw toggle) and not here.
+	 */
+	if (c->mode == LTC2688_MODE_DEFAULT)
+		reg = LTC2688_CMD_CH_CODE_UPDATE(chan);
+	else
+		reg = LTC2688_CMD_CH_CODE(chan);
+
+	ret = regmap_write(st->regmap, reg, code);
+out_unlock:
+	mutex_unlock(&st->lock);
+	return ret;
+}
+
+static int ltc2688_dac_code_read(struct ltc2688_state *st, u32 chan, u32 input,
+				 u32 *code)
+{
+	struct ltc2688_chan *c = &st->channels[chan];
+	int ret;
+
+	mutex_lock(&st->lock);
+	ret = regmap_update_bits(st->regmap, LTC2688_CMD_A_B_SELECT, BIT(chan),
+				 input << chan);
+	if (ret)
+		goto out_unlock;
+
+	ret = regmap_read(st->regmap, LTC2688_CMD_CH_CODE(chan), code);
+out_unlock:
+	mutex_unlock(&st->lock);
+
+	if (!c->toggle_chan && input == LTC2688_INPUT_B)
+		*code = FIELD_GET(LTC2688_DITHER_RAW_MASK, *code);
+
+	return ret;
+}
+
+static const int ltc2688_raw_range[] = {0, 1, U16_MAX};
+
+static int ltc2688_read_avail(struct iio_dev *indio_dev,
+			      struct iio_chan_spec const *chan,
+			      const int **vals, int *type, int *length,
+			      long info)
+{
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		*vals = ltc2688_raw_range;
+		*type = IIO_VAL_INT;
+		return IIO_AVAIL_RANGE;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int ltc2688_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long info)
+{
+	struct ltc2688_state *st = iio_priv(indio_dev);
+	int ret;
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		ret = ltc2688_dac_code_read(st, chan->channel, LTC2688_INPUT_A,
+					    val);
+		if (ret)
+			return ret;
+
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_OFFSET:
+		ret = ltc2688_offset_get(st, chan->channel, val);
+		if (ret)
+			return ret;
+
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		ret = ltc2688_scale_get(st, chan->channel, val);
+		if (ret)
+			return ret;
+
+		*val = 16;
+		return IIO_VAL_FRACTIONAL_LOG2;
+	case IIO_CHAN_INFO_CALIBBIAS:
+		ret = regmap_read(st->regmap,
+				  LTC2688_CMD_CH_OFFSET(chan->channel), val);
+		if (ret)
+			return ret;
+
+		*val = FIELD_GET(LTC2688_CH_CALIBBIAS_MASK, *val);
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_CALIBSCALE:
+		ret = regmap_read(st->regmap,
+				  LTC2688_CMD_CH_GAIN(chan->channel), val);
+		if (ret)
+			return ret;
+
+		return IIO_VAL_INT;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int ltc2688_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan, int val,
+			     int val2, long info)
+{
+	struct ltc2688_state *st = iio_priv(indio_dev);
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		if (val > U16_MAX || val < 0)
+			return -EINVAL;
+
+		return ltc2688_dac_code_write(st, chan->channel,
+					      LTC2688_INPUT_A, val);
+	case IIO_CHAN_INFO_CALIBBIAS:
+		if (val > LTC2688_CH_CALIBBIAS_MAX_VAL)
+			return -EINVAL;
+
+		return regmap_write(st->regmap,
+				    LTC2688_CMD_CH_OFFSET(chan->channel),
+				    FIELD_PREP(LTC2688_CH_CALIBBIAS_MASK, val));
+	case IIO_CHAN_INFO_CALIBSCALE:
+		return regmap_write(st->regmap,
+				    LTC2688_CMD_CH_GAIN(chan->channel), val);
+	default:
+		return -EINVAL;
+	}
+}
+
+static ssize_t ltc2688_dither_toggle_set(struct iio_dev *indio_dev,
+					 uintptr_t private,
+					 const struct iio_chan_spec *chan,
+					 const char *buf, size_t len)
+{
+	struct ltc2688_state *st = iio_priv(indio_dev);
+	struct ltc2688_chan *c = &st->channels[chan->channel];
+	int ret;
+	bool en;
+
+	ret = kstrtobool(buf, &en);
+	if (ret)
+		return ret;
+
+	mutex_lock(&st->lock);
+	ret = regmap_update_bits(st->regmap, LTC2688_CMD_TOGGLE_DITHER_EN,
+				 BIT(chan->channel), en << chan->channel);
+	if (ret)
+		goto out_unlock;
+
+	c->mode = en ? LTC2688_MODE_DITHER_TOGGLE : LTC2688_MODE_DEFAULT;
+out_unlock:
+	mutex_unlock(&st->lock);
+
+	return ret ?: len;
+}
+
+static ssize_t ltc2688_reg_bool_get(struct iio_dev *indio_dev,
+				    uintptr_t private,
+				    const struct iio_chan_spec *chan,
+				    char *buf)
+{
+	const struct ltc2688_state *st = iio_priv(indio_dev);
+	int ret;
+	u32 val;
+
+	ret = regmap_read(st->regmap, private, &val);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%u\n", !!(val & BIT(chan->channel)));
+}
+
+static ssize_t ltc2688_reg_bool_set(struct iio_dev *indio_dev,
+				    uintptr_t private,
+				    const struct iio_chan_spec *chan,
+				    const char *buf, size_t len)
+{
+	const struct ltc2688_state *st = iio_priv(indio_dev);
+	int ret;
+	bool en;
+
+	ret = kstrtobool(buf, &en);
+	if (ret)
+		return ret;
+
+	ret = regmap_update_bits(st->regmap, private, BIT(chan->channel),
+				 en << chan->channel);
+	if (ret)
+		return ret;
+
+	return len;
+}
+
+static ssize_t ltc2688_dither_freq_avail(const struct ltc2688_state *st,
+					 const struct ltc2688_chan *chan,
+					 char *buf)
+{
+	int sz = 0;
+	u32 f;
+
+	for (f = 0; f < ARRAY_SIZE(chan->dither_frequency); f++)
+		sz += sysfs_emit_at(buf, sz, "%ld ", chan->dither_frequency[f]);
+
+	buf[sz - 1] = '\n';
+
+	return sz;
+}
+
+static ssize_t ltc2688_dither_freq_get(struct iio_dev *indio_dev,
+				       uintptr_t private,
+				       const struct iio_chan_spec *chan,
+				       char *buf)
+{
+	const struct ltc2688_state *st = iio_priv(indio_dev);
+	const struct ltc2688_chan *c = &st->channels[chan->channel];
+	u32 reg, freq;
+	int ret;
+
+	if (private == LTC2688_DITHER_FREQ_AVAIL)
+		return ltc2688_dither_freq_avail(st, c, buf);
+
+	ret = regmap_read(st->regmap, LTC2688_CMD_CH_SETTING(chan->channel),
+			  &reg);
+	if (ret)
+		return ret;
+
+	freq = FIELD_GET(LTC2688_CH_DIT_PER_MSK, reg);
+	if (freq >= ARRAY_SIZE(c->dither_frequency))
+		return -EIO;
+
+	return sysfs_emit(buf, "%ld\n", c->dither_frequency[freq]);
+}
+
+static ssize_t ltc2688_dither_freq_set(struct iio_dev *indio_dev,
+				       uintptr_t private,
+				       const struct iio_chan_spec *chan,
+				       const char *buf, size_t len)
+{
+	const struct ltc2688_state *st = iio_priv(indio_dev);
+	const struct ltc2688_chan *c = &st->channels[chan->channel];
+	long val;
+	u32 freq;
+	int ret;
+
+	if (private == LTC2688_DITHER_FREQ_AVAIL)
+		return -EINVAL;
+
+	ret = kstrtol(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	for (freq = 0; freq < ARRAY_SIZE(c->dither_frequency); freq++) {
+		if (val == c->dither_frequency[freq])
+			break;
+	}
+
+	if (freq == ARRAY_SIZE(c->dither_frequency))
+		return -EINVAL;
+
+	ret = regmap_update_bits(st->regmap,
+				 LTC2688_CMD_CH_SETTING(chan->channel),
+				 LTC2688_CH_DIT_PER_MSK,
+				 FIELD_PREP(LTC2688_CH_DIT_PER_MSK, freq));
+	if (ret)
+		return ret;
+
+	return len;
+}
+
+static ssize_t ltc2688_dac_input_read(struct iio_dev *indio_dev,
+				      uintptr_t private,
+				      const struct iio_chan_spec *chan,
+				      char *buf)
+{
+	struct ltc2688_state *st = iio_priv(indio_dev);
+	int ret;
+	u32 val;
+
+	if (private == LTC2688_INPUT_B_AVAIL)
+		return sysfs_emit(buf, "[%u %u %u]\n", ltc2688_raw_range[0],
+				  ltc2688_raw_range[1],
+				  ltc2688_raw_range[2] / 4);
+
+	if (private == LTC2688_DITHER_OFF)
+		return sysfs_emit(buf, "0\n");
+
+	ret = ltc2688_dac_code_read(st, chan->channel, private, &val);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%u\n", val);
+}
+
+static ssize_t ltc2688_dac_input_write(struct iio_dev *indio_dev,
+				       uintptr_t private,
+				       const struct iio_chan_spec *chan,
+				       const char *buf, size_t len)
+{
+	struct ltc2688_state *st = iio_priv(indio_dev);
+	int ret;
+	u16 val;
+
+	if (private == LTC2688_INPUT_B_AVAIL || private == LTC2688_DITHER_OFF)
+		return -EINVAL;
+
+	ret = kstrtou16(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	ret = ltc2688_dac_code_write(st, chan->channel, private, val);
+	if (ret)
+		return ret;
+
+	return len;
+}
+
+static int ltc2688_get_dither_phase(struct iio_dev *dev,
+				    const struct iio_chan_spec *chan)
+{
+	struct ltc2688_state *st = iio_priv(dev);
+	int ret, regval;
+
+	ret = regmap_read(st->regmap, LTC2688_CMD_CH_SETTING(chan->channel),
+			  &regval);
+	if (ret)
+		return ret;
+
+	return FIELD_GET(LTC2688_CH_DIT_PH_MSK, regval);
+}
+
+static int ltc2688_set_dither_phase(struct iio_dev *dev,
+				    const struct iio_chan_spec *chan,
+				    unsigned int phase)
+{
+	struct ltc2688_state *st = iio_priv(dev);
+
+	return regmap_update_bits(st->regmap,
+				  LTC2688_CMD_CH_SETTING(chan->channel),
+				  LTC2688_CH_DIT_PH_MSK,
+				  FIELD_PREP(LTC2688_CH_DIT_PH_MSK, phase));
+}
+
+static int ltc2688_reg_access(struct iio_dev *indio_dev,
+			      unsigned int reg,
+			      unsigned int writeval,
+			      unsigned int *readval)
+{
+	struct ltc2688_state *st = iio_priv(indio_dev);
+
+	if (readval)
+		return regmap_read(st->regmap, reg, readval);
+
+	return regmap_write(st->regmap, reg, writeval);
+}
+
+static const char * const ltc2688_dither_phase[] = {
+	"0", "1.5708", "3.14159", "4.71239",
+};
+
+static const struct iio_enum ltc2688_dither_phase_enum = {
+	.items = ltc2688_dither_phase,
+	.num_items = ARRAY_SIZE(ltc2688_dither_phase),
+	.set = ltc2688_set_dither_phase,
+	.get = ltc2688_get_dither_phase,
+};
+
+#define LTC2688_CHAN_EXT_INFO(_name, _what, _shared, _read, _write) {	\
+	.name = _name,							\
+	.read = (_read),						\
+	.write = (_write),						\
+	.private = (_what),						\
+	.shared = (_shared),						\
+}
+
+/*
+ * For toggle mode we only expose the symbol attr (sw_toggle) in case a TGPx is
+ * not provided in dts.
+ */
+static const struct iio_chan_spec_ext_info ltc2688_toggle_sym_ext_info[] = {
+	LTC2688_CHAN_EXT_INFO("raw0", LTC2688_INPUT_A, IIO_SEPARATE,
+			      ltc2688_dac_input_read, ltc2688_dac_input_write),
+	LTC2688_CHAN_EXT_INFO("raw1", LTC2688_INPUT_B, IIO_SEPARATE,
+			      ltc2688_dac_input_read, ltc2688_dac_input_write),
+	LTC2688_CHAN_EXT_INFO("toggle_en", LTC2688_CMD_TOGGLE_DITHER_EN,
+			      IIO_SEPARATE, ltc2688_reg_bool_get,
+			      ltc2688_dither_toggle_set),
+	LTC2688_CHAN_EXT_INFO("powerdown", LTC2688_CMD_POWERDOWN, IIO_SEPARATE,
+			      ltc2688_reg_bool_get, ltc2688_reg_bool_set),
+	LTC2688_CHAN_EXT_INFO("symbol", LTC2688_CMD_SW_TOGGLE, IIO_SEPARATE,
+			      ltc2688_reg_bool_get, ltc2688_reg_bool_set),
+	{}
+};
+
+static const struct iio_chan_spec_ext_info ltc2688_toggle_ext_info[] = {
+	LTC2688_CHAN_EXT_INFO("raw0", LTC2688_INPUT_A, IIO_SEPARATE,
+			      ltc2688_dac_input_read, ltc2688_dac_input_write),
+	LTC2688_CHAN_EXT_INFO("raw1", LTC2688_INPUT_B, IIO_SEPARATE,
+			      ltc2688_dac_input_read, ltc2688_dac_input_write),
+	LTC2688_CHAN_EXT_INFO("toggle_en", LTC2688_CMD_TOGGLE_DITHER_EN,
+			      IIO_SEPARATE, ltc2688_reg_bool_get,
+			      ltc2688_dither_toggle_set),
+	LTC2688_CHAN_EXT_INFO("powerdown", LTC2688_CMD_POWERDOWN, IIO_SEPARATE,
+			      ltc2688_reg_bool_get, ltc2688_reg_bool_set),
+	{}
+};
+
+static struct iio_chan_spec_ext_info ltc2688_dither_ext_info[] = {
+	LTC2688_CHAN_EXT_INFO("dither_raw", LTC2688_INPUT_B, IIO_SEPARATE,
+			      ltc2688_dac_input_read, ltc2688_dac_input_write),
+	LTC2688_CHAN_EXT_INFO("dither_raw_available", LTC2688_INPUT_B_AVAIL,
+			      IIO_SEPARATE, ltc2688_dac_input_read,
+			      ltc2688_dac_input_write),
+	LTC2688_CHAN_EXT_INFO("dither_offset", LTC2688_DITHER_OFF, IIO_SEPARATE,
+			      ltc2688_dac_input_read, ltc2688_dac_input_write),
+	/*
+	 * Not IIO_ENUM because the available freq needs to be computed at
+	 * probe. We could still use it, but it didn't felt much right.
+	 */
+	LTC2688_CHAN_EXT_INFO("dither_frequency", 0, IIO_SEPARATE,
+			      ltc2688_dither_freq_get, ltc2688_dither_freq_set),
+	LTC2688_CHAN_EXT_INFO("dither_frequency_available",
+			      LTC2688_DITHER_FREQ_AVAIL, IIO_SEPARATE,
+			      ltc2688_dither_freq_get, ltc2688_dither_freq_set),
+	IIO_ENUM("dither_phase", IIO_SEPARATE, &ltc2688_dither_phase_enum),
+	IIO_ENUM_AVAILABLE("dither_phase", IIO_SEPARATE,
+			   &ltc2688_dither_phase_enum),
+	LTC2688_CHAN_EXT_INFO("dither_en", LTC2688_CMD_TOGGLE_DITHER_EN,
+			      IIO_SEPARATE, ltc2688_reg_bool_get,
+			      ltc2688_dither_toggle_set),
+	LTC2688_CHAN_EXT_INFO("powerdown", LTC2688_CMD_POWERDOWN, IIO_SEPARATE,
+			      ltc2688_reg_bool_get, ltc2688_reg_bool_set),
+	{}
+};
+
+static const struct iio_chan_spec_ext_info ltc2688_ext_info[] = {
+	LTC2688_CHAN_EXT_INFO("powerdown", LTC2688_CMD_POWERDOWN, IIO_SEPARATE,
+			      ltc2688_reg_bool_get, ltc2688_reg_bool_set),
+	{}
+};
+
+#define LTC2688_CHANNEL(_chan) {					\
+	.type = IIO_VOLTAGE,						\
+	.indexed = 1,							\
+	.output = 1,							\
+	.channel = (_chan),						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_CALIBSCALE) |		\
+		BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET) |	\
+		BIT(IIO_CHAN_INFO_CALIBBIAS) | BIT(IIO_CHAN_INFO_RAW),	\
+	.info_mask_separate_available = BIT(IIO_CHAN_INFO_RAW),		\
+	.ext_info = ltc2688_ext_info,					\
+}
+
+static const struct iio_chan_spec ltc2688_channels[] = {
+	LTC2688_CHANNEL(0),
+	LTC2688_CHANNEL(1),
+	LTC2688_CHANNEL(2),
+	LTC2688_CHANNEL(3),
+	LTC2688_CHANNEL(4),
+	LTC2688_CHANNEL(5),
+	LTC2688_CHANNEL(6),
+	LTC2688_CHANNEL(7),
+	LTC2688_CHANNEL(8),
+	LTC2688_CHANNEL(9),
+	LTC2688_CHANNEL(10),
+	LTC2688_CHANNEL(11),
+	LTC2688_CHANNEL(12),
+	LTC2688_CHANNEL(13),
+	LTC2688_CHANNEL(14),
+	LTC2688_CHANNEL(15),
+};
+
+static void ltc2688_clk_disable(void *clk)
+{
+	clk_disable_unprepare(clk);
+}
+
+static const int ltc2688_period[LTC2688_DITHER_FREQ_AVAIL_N] = {
+	4, 8, 16, 32, 64,
+};
+
+static int ltc2688_tgp_clk_setup(struct ltc2688_state *st,
+				 struct ltc2688_chan *chan,
+				 struct fwnode_handle *node, int tgp)
+{
+	unsigned long rate;
+	struct clk *clk;
+	int ret, f;
+
+	clk = devm_get_clk_from_child(&st->spi->dev, to_of_node(node), NULL);
+	if (IS_ERR(clk))
+		return dev_err_probe(&st->spi->dev, PTR_ERR(clk),
+				     "failed to get tgp clk.\n");
+
+	ret = clk_prepare_enable(clk);
+	if (ret)
+		return dev_err_probe(&st->spi->dev, ret,
+				     "failed to enable tgp clk.\n");
+
+	ret = devm_add_action_or_reset(&st->spi->dev, ltc2688_clk_disable, clk);
+	if (ret)
+		return ret;
+
+	if (chan->toggle_chan)
+		return 0;
+
+	/* calculate available dither frequencies */
+	rate = clk_get_rate(clk);
+	for (f = 0; f < ARRAY_SIZE(chan->dither_frequency); f++)
+		chan->dither_frequency[f] = DIV_ROUND_CLOSEST(rate, ltc2688_period[f]);
+
+	return 0;
+}
+
+static int ltc2688_span_lookup(const struct ltc2688_state *st, int min, int max)
+{
+	u32 span;
+
+	for (span = 0; span < ARRAY_SIZE(ltc2688_span_helper); span++) {
+		if (min == ltc2688_span_helper[span][0] &&
+		    max == ltc2688_span_helper[span][1])
+			return span;
+	}
+
+	return -EINVAL;
+}
+
+static int ltc2688_channel_config(struct ltc2688_state *st)
+{
+	struct device *dev = &st->spi->dev;
+	struct fwnode_handle *child;
+	u32 reg, clk_input, val, tmp[2];
+	int ret, span;
+
+	device_for_each_child_node(dev, child) {
+		struct ltc2688_chan *chan;
+
+		ret = fwnode_property_read_u32(child, "reg", &reg);
+		if (ret) {
+			fwnode_handle_put(child);
+			return dev_err_probe(dev, ret,
+					     "Failed to get reg property\n");
+		}
+
+		if (reg >= LTC2688_DAC_CHANNELS) {
+			fwnode_handle_put(child);
+			return dev_err_probe(dev, -EINVAL,
+					     "reg bigger than: %d\n",
+					     LTC2688_DAC_CHANNELS);
+		}
+
+		val = 0;
+		chan = &st->channels[reg];
+		if (fwnode_property_read_bool(child, "adi,toggle-mode")) {
+			chan->toggle_chan = true;
+			/* assume sw toggle ABI */
+			st->iio_chan[reg].ext_info = ltc2688_toggle_sym_ext_info;
+			/*
+			 * Clear IIO_CHAN_INFO_RAW bit as toggle channels expose
+			 * out_voltage_raw{0|1} files.
+			 */
+			__clear_bit(IIO_CHAN_INFO_RAW,
+				    &st->iio_chan[reg].info_mask_separate);
+		}
+
+		ret = fwnode_property_read_u32_array(child, "adi,output-range-microvolt",
+						     tmp, ARRAY_SIZE(tmp));
+		if (!ret) {
+			span = ltc2688_span_lookup(st, (int)tmp[0] / 1000,
+						   tmp[1] / 1000);
+			if (span < 0) {
+				fwnode_handle_put(child);
+				return dev_err_probe(dev, -EINVAL,
+						     "output range not valid:[%d %d]\n",
+						     tmp[0], tmp[1]);
+			}
+
+			val |= FIELD_PREP(LTC2688_CH_SPAN_MSK, span);
+		}
+
+		ret = fwnode_property_read_u32(child, "adi,toggle-dither-input",
+					       &clk_input);
+		if (!ret) {
+			if (clk_input >= LTC2688_CH_TGP_MAX) {
+				fwnode_handle_put(child);
+				return dev_err_probe(dev, -EINVAL,
+						     "toggle-dither-input inv value(%d)\n",
+						     clk_input);
+			}
+
+			ret = ltc2688_tgp_clk_setup(st, chan, child, clk_input);
+			if (ret) {
+				fwnode_handle_put(child);
+				return ret;
+			}
+
+			/*
+			 * 0 means software toggle which is the default mode.
+			 * Hence the +1.
+			 */
+			val |= FIELD_PREP(LTC2688_CH_TD_SEL_MSK, clk_input + 1);
+
+			/*
+			 * If a TGPx is given, we automatically assume a dither
+			 * capable channel (unless toggle is already enabled).
+			 * On top of this we just set here the dither bit in the
+			 * channel settings. It won't have any effect until the
+			 * global toggle/dither bit is enabled.
+			 */
+			if (!chan->toggle_chan) {
+				val |= FIELD_PREP(LTC2688_CH_MODE_MSK, 1);
+				st->iio_chan[reg].ext_info = ltc2688_dither_ext_info;
+			} else {
+				/* wait, no sw toggle after all */
+				st->iio_chan[reg].ext_info = ltc2688_toggle_ext_info;
+			}
+		}
+
+		if (fwnode_property_read_bool(child, "adi,overrange")) {
+			chan->overrange = true;
+			val |= LTC2688_CH_OVERRANGE_MSK;
+		}
+
+		if (!val)
+			continue;
+
+		ret = regmap_write(st->regmap, LTC2688_CMD_CH_SETTING(reg),
+				   val);
+		if (ret) {
+			fwnode_handle_put(child);
+			return dev_err_probe(dev, -EINVAL,
+					     "failed to set chan settings\n");
+		}
+	}
+
+	return 0;
+}
+
+static int ltc2688_setup(struct ltc2688_state *st, struct regulator *vref)
+{
+	struct gpio_desc *gpio;
+	int ret;
+
+	/*
+	 * If we have a reset pin, use that to reset the board, If not, use
+	 * the reset bit.
+	 */
+	gpio = devm_gpiod_get_optional(&st->spi->dev, "clr", GPIOD_OUT_HIGH);
+	if (IS_ERR(gpio))
+		return dev_err_probe(&st->spi->dev, PTR_ERR(gpio),
+				     "Failed to get reset gpio");
+	if (gpio) {
+		usleep_range(1000, 1200);
+		/* bring device out of reset */
+		gpiod_set_value_cansleep(gpio, 0);
+	} else {
+		ret = regmap_update_bits(st->regmap, LTC2688_CMD_CONFIG,
+					 LTC2688_CONFIG_RST,
+					 LTC2688_CONFIG_RST);
+		if (ret)
+			return ret;
+	}
+
+	usleep_range(10000, 12000);
+
+	/*
+	 * Duplicate the default channel configuration as it can change during
+	 * @ltc2688_channel_config()
+	 */
+	st->iio_chan = devm_kmemdup(&st->spi->dev, ltc2688_channels,
+				    sizeof(ltc2688_channels), GFP_KERNEL);
+	if (!st->iio_chan)
+		return -ENOMEM;
+
+	ret = ltc2688_channel_config(st);
+	if (ret)
+		return ret;
+
+	if (!vref)
+		return 0;
+
+	return regmap_set_bits(st->regmap, LTC2688_CMD_CONFIG,
+			       LTC2688_CONFIG_EXT_REF);
+}
+
+static void ltc2688_disable_regulators(void *data)
+{
+	struct ltc2688_state *st = data;
+
+	regulator_bulk_disable(ARRAY_SIZE(st->regulators), st->regulators);
+}
+
+static void ltc2688_disable_regulator(void *regulator)
+{
+	regulator_disable(regulator);
+}
+
+static bool ltc2688_reg_readable(struct device *dev, unsigned int reg)
+{
+	switch (reg) {
+	case LTC2688_CMD_CH_CODE(0) ... LTC2688_CMD_CH_GAIN(15):
+		return true;
+	case LTC2688_CMD_CONFIG ... LTC2688_CMD_THERMAL_STAT:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool ltc2688_reg_writable(struct device *dev, unsigned int reg)
+{
+	/*
+	 * There's a jump from 0x76 to 0x78 in the write codes and the thermal
+	 * status code is 0x77 (which is read only) so that we need to check
+	 * that special condition.
+	 */
+	if (reg <= LTC2688_CMD_UPDATE_ALL && reg != LTC2688_CMD_THERMAL_STAT)
+		return true;
+
+	return false;
+}
+
+static struct regmap_bus ltc2688_regmap_bus = {
+	.read = ltc2688_spi_read,
+	.write = ltc2688_spi_write,
+	.read_flag_mask = LTC2688_READ_OPERATION,
+	.reg_format_endian_default = REGMAP_ENDIAN_BIG,
+	.val_format_endian_default = REGMAP_ENDIAN_BIG,
+};
+
+static const struct regmap_config ltc2688_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 16,
+	.readable_reg = ltc2688_reg_readable,
+	.writeable_reg = ltc2688_reg_writable,
+	/* ignoring the no op command */
+	.max_register = LTC2688_CMD_UPDATE_ALL,
+};
+
+static const struct iio_info ltc2688_info = {
+	.write_raw = ltc2688_write_raw,
+	.read_raw = ltc2688_read_raw,
+	.read_avail = ltc2688_read_avail,
+	.debugfs_reg_access = ltc2688_reg_access,
+};
+
+static int ltc2688_probe(struct spi_device *spi)
+{
+	struct ltc2688_state *st;
+	struct iio_dev *indio_dev;
+	struct regulator *vref_reg;
+	struct device *dev = &spi->dev;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	st = iio_priv(indio_dev);
+	st->spi = spi;
+
+	/* Just write this once. No need to do it in every regmap read. */
+	st->tx_data[3] = LTC2688_CMD_NOOP;
+	mutex_init(&st->lock);
+
+	st->regmap = devm_regmap_init(dev, &ltc2688_regmap_bus, st,
+				      &ltc2688_regmap_config);
+	if (IS_ERR(st->regmap))
+		return dev_err_probe(dev, PTR_ERR(st->regmap),
+				     "Failed to init regmap");
+
+	st->regulators[0].supply = "vcc";
+	st->regulators[1].supply = "iovcc";
+	ret = devm_regulator_bulk_get(dev, ARRAY_SIZE(st->regulators),
+				      st->regulators);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to get regulators\n");
+
+	ret = regulator_bulk_enable(ARRAY_SIZE(st->regulators), st->regulators);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to enable regulators\n");
+
+	ret = devm_add_action_or_reset(dev, ltc2688_disable_regulators, st);
+	if (ret)
+		return ret;
+
+	vref_reg = devm_regulator_get_optional(dev, "vref");
+	if (IS_ERR(vref_reg)) {
+		if (PTR_ERR(vref_reg) != -ENODEV)
+			return dev_err_probe(dev, PTR_ERR(vref_reg),
+					     "Failed to get vref regulator");
+
+		vref_reg = NULL;
+		/* internal reference */
+		st->vref = 4096;
+	} else {
+		ret = regulator_enable(vref_reg);
+		if (ret)
+			return dev_err_probe(dev, ret,
+					     "Failed to enable vref regulators\n");
+
+		ret = devm_add_action_or_reset(dev, ltc2688_disable_regulator,
+					       vref_reg);
+		if (ret)
+			return ret;
+
+		ret = regulator_get_voltage(vref_reg);
+		if (ret < 0)
+			return dev_err_probe(dev, ret, "Failed to get vref\n");
+
+		st->vref = ret / 1000;
+	}
+
+	ret = ltc2688_setup(st, vref_reg);
+	if (ret)
+		return ret;
+
+	indio_dev->name = "ltc2688";
+	indio_dev->info = &ltc2688_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = st->iio_chan;
+	indio_dev->num_channels = ARRAY_SIZE(ltc2688_channels);
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct of_device_id ltc2688_of_id[] = {
+	{ .compatible = "adi,ltc2688" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, ltc2688_of_id);
+
+static const struct spi_device_id ltc2688_id[] = {
+	{ "ltc2688" },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, ltc2688_id);
+
+static struct spi_driver ltc2688_driver = {
+	.driver = {
+		.name = "ltc2688",
+		.of_match_table = ltc2688_of_id,
+	},
+	.probe = ltc2688_probe,
+	.id_table = ltc2688_id,
+};
+module_spi_driver(ltc2688_driver);
+
+MODULE_AUTHOR("Nuno Sá <nuno.sa@analog.com>");
+MODULE_DESCRIPTION("Analog Devices LTC2688 DAC");
+MODULE_LICENSE("GPL");