[PATCH v7 6/7] iio: adc: Add support for AD4000

[Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>]

Add support for AD4000 series of low noise, low power, high speed,
successive approximation register (SAR) ADCs.

Reviewed-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
Reviewed-by: David Lechner <dlechner@xxxxxxxxxxxx>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>
---
Last remaining bit was to use spi_w8r8() for reg read.
Here's what I tried:

static int ad4000_read_reg(struct ad4000_state *st, unsigned int *val)
{
	ssize_t ret;

	ret = spi_w8r8(st->spi, AD4000_READ_COMMAND);
	if (ret < 0)
		return ret;

	*val = ret;
	return 0;
}

For register read, the SPI transfer line states seen on FPGA hardware monitor
debug tool were as expected and the data entailed by those signals was correct.
Though, the values read back from spi_w8r8() were alternating between the
correct expected value and 0xFF (sometimes 0x00).
single-shot read values (read_raw) were coming with an unusual 8 data point
"delay"/latency.
After some time experimenting with those, the sample read buffer also got
"corrupted" such that, despite ADC readings being correct on SPI lines, the
values read back in the driver were not the same.
Even after all of that, reg access (write/read) kept working on SPI lines.
I'm thinking maybe this is not a critical feature so going with
spi_sync_transfer() until a way of doing reg read with spi_w8r8() is found.

 MAINTAINERS              |   1 +
 drivers/iio/adc/Kconfig  |  12 +
 drivers/iio/adc/Makefile |   1 +
 drivers/iio/adc/ad4000.c | 722 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 736 insertions(+)
 create mode 100644 drivers/iio/adc/ad4000.c

diff --git a/MAINTAINERS b/MAINTAINERS
index e03300d3ef13..88c32e4364d9 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1205,6 +1205,7 @@ L:	linux-iio@xxxxxxxxxxxxxxx
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/adc/adi,ad4000.yaml
+F:	drivers/iio/adc/ad4000.c
 
 ANALOG DEVICES INC AD4130 DRIVER
 M:	Cosmin Tanislav <cosmin.tanislav@xxxxxxxxxx>
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index f60fe85a30d5..d90096fe32e7 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -21,6 +21,18 @@ config AD_SIGMA_DELTA
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 
+config AD4000
+	tristate "Analog Devices AD4000 ADC Driver"
+	depends on SPI
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say yes here to build support for Analog Devices AD4000 high speed
+	  SPI analog to digital converters (ADC).
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called ad4000.
+
 config AD4130
 	tristate "Analog Device AD4130 ADC Driver"
 	depends on SPI
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index d370e066544e..30cacd1d219c 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -6,6 +6,7 @@
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_AB8500_GPADC) += ab8500-gpadc.o
 obj-$(CONFIG_AD_SIGMA_DELTA) += ad_sigma_delta.o
+obj-$(CONFIG_AD4000) += ad4000.o
 obj-$(CONFIG_AD4130) += ad4130.o
 obj-$(CONFIG_AD7091R) += ad7091r-base.o
 obj-$(CONFIG_AD7091R5) += ad7091r5.o
diff --git a/drivers/iio/adc/ad4000.c b/drivers/iio/adc/ad4000.c
new file mode 100644
index 000000000000..6ea491245084
--- /dev/null
+++ b/drivers/iio/adc/ad4000.c
@@ -0,0 +1,722 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * AD4000 SPI ADC driver
+ *
+ * Copyright 2024 Analog Devices Inc.
+ */
+#include <linux/bits.h>
+#include <linux/bitfield.h>
+#include <linux/byteorder/generic.h>
+#include <linux/cleanup.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/gpio/consumer.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+#include <linux/units.h>
+#include <linux/util_macros.h>
+#include <linux/iio/iio.h>
+
+#include <linux/iio/buffer.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
+
+#define AD4000_READ_COMMAND	0x54
+#define AD4000_WRITE_COMMAND	0x14
+
+#define AD4000_CONFIG_REG_DEFAULT	0xE1
+
+/* AD4000 Configuration Register programmable bits */
+#define AD4000_CFG_SPAN_COMP		BIT(3) /* Input span compression  */
+#define AD4000_CFG_HIGHZ		BIT(2) /* High impedance mode  */
+
+#define AD4000_SCALE_OPTIONS		2
+
+#define AD4000_TQUIET1_NS		190
+#define AD4000_TQUIET2_NS		60
+#define AD4000_TCONV_NS			320
+
+#define __AD4000_DIFF_CHANNEL(_sign, _real_bits, _storage_bits, _reg_access)	\
+{										\
+	.type = IIO_VOLTAGE,							\
+	.indexed = 1,								\
+	.differential = 1,							\
+	.channel = 0,								\
+	.channel2 = 1,								\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |				\
+			      BIT(IIO_CHAN_INFO_SCALE),				\
+	.info_mask_separate_available = _reg_access ? BIT(IIO_CHAN_INFO_SCALE) : 0,\
+	.scan_type = {								\
+		.sign = _sign,							\
+		.realbits = _real_bits,						\
+		.storagebits = _storage_bits,					\
+		.shift = _storage_bits - _real_bits,				\
+		.endianness = IIO_BE,						\
+	},									\
+}
+
+#define AD4000_DIFF_CHANNEL(_sign, _real_bits, _reg_access)			\
+	__AD4000_DIFF_CHANNEL((_sign), (_real_bits),				\
+				     ((_real_bits) > 16 ? 32 : 16), (_reg_access))
+
+#define __AD4000_PSEUDO_DIFF_CHANNEL(_sign, _real_bits, _storage_bits, _reg_access)\
+{										\
+	.type = IIO_VOLTAGE,							\
+	.indexed = 1,								\
+	.channel = 0,								\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |				\
+			      BIT(IIO_CHAN_INFO_SCALE) |			\
+			      BIT(IIO_CHAN_INFO_OFFSET),			\
+	.info_mask_separate_available = _reg_access ? BIT(IIO_CHAN_INFO_SCALE) : 0,\
+	.scan_type = {								\
+		.sign = _sign,							\
+		.realbits = _real_bits,						\
+		.storagebits = _storage_bits,					\
+		.shift = _storage_bits - _real_bits,				\
+		.endianness = IIO_BE,						\
+	},									\
+}
+
+#define AD4000_PSEUDO_DIFF_CHANNEL(_sign, _real_bits, _reg_access)		\
+	__AD4000_PSEUDO_DIFF_CHANNEL((_sign), (_real_bits),			\
+				     ((_real_bits) > 16 ? 32 : 16), (_reg_access))
+
+static const char * const ad4000_power_supplies[] = {
+	"vdd", "vio"
+};
+
+enum ad4000_sdi {
+	AD4000_SDI_MOSI,
+	AD4000_SDI_VIO,
+	AD4000_SDI_CS,
+	AD4000_SDI_GND,
+};
+
+/* maps adi,sdi-pin property value to enum */
+static const char * const ad4000_sdi_pin[] = {
+	[AD4000_SDI_MOSI] = "sdi",
+	[AD4000_SDI_VIO] = "high",
+	[AD4000_SDI_CS] = "cs",
+	[AD4000_SDI_GND] = "low",
+};
+
+/* Gains stored as fractions of 1000 so they can be expressed by integers. */
+static const int ad4000_gains[] = {
+	454, 909, 1000, 1900,
+};
+
+struct ad4000_chip_info {
+	const char *dev_name;
+	struct iio_chan_spec chan_spec;
+	struct iio_chan_spec reg_access_chan_spec;
+	bool has_hardware_gain;
+};
+
+static const struct ad4000_chip_info ad4000_chip_info = {
+	.dev_name = "ad4000",
+	.chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 16, 0),
+	.reg_access_chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 16, 1),
+};
+
+static const struct ad4000_chip_info ad4001_chip_info = {
+	.dev_name = "ad4001",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 16, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 16, 1),
+};
+
+static const struct ad4000_chip_info ad4002_chip_info = {
+	.dev_name = "ad4002",
+	.chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 18, 0),
+	.reg_access_chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 18, 1),
+};
+
+static const struct ad4000_chip_info ad4003_chip_info = {
+	.dev_name = "ad4003",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 18, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 18, 1),
+};
+
+static const struct ad4000_chip_info ad4004_chip_info = {
+	.dev_name = "ad4004",
+	.chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 16, 0),
+	.reg_access_chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 16, 1),
+};
+
+static const struct ad4000_chip_info ad4005_chip_info = {
+	.dev_name = "ad4005",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 16, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 16, 1),
+};
+
+static const struct ad4000_chip_info ad4006_chip_info = {
+	.dev_name = "ad4006",
+	.chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 18, 0),
+	.reg_access_chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 18, 1),
+};
+
+static const struct ad4000_chip_info ad4007_chip_info = {
+	.dev_name = "ad4007",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 18, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 18, 1),
+};
+
+static const struct ad4000_chip_info ad4008_chip_info = {
+	.dev_name = "ad4008",
+	.chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 16, 0),
+	.reg_access_chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 16, 1),
+};
+
+static const struct ad4000_chip_info ad4010_chip_info = {
+	.dev_name = "ad4010",
+	.chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 18, 0),
+	.reg_access_chan_spec = AD4000_PSEUDO_DIFF_CHANNEL('u', 18, 1),
+};
+
+static const struct ad4000_chip_info ad4011_chip_info = {
+	.dev_name = "ad4011",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 18, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 18, 1),
+};
+
+static const struct ad4000_chip_info ad4020_chip_info = {
+	.dev_name = "ad4020",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 20, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 20, 1),
+};
+
+static const struct ad4000_chip_info ad4021_chip_info = {
+	.dev_name = "ad4021",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 20, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 20, 1),
+};
+
+static const struct ad4000_chip_info ad4022_chip_info = {
+	.dev_name = "ad4022",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 20, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 20, 1),
+};
+
+static const struct ad4000_chip_info adaq4001_chip_info = {
+	.dev_name = "adaq4001",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 16, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 16, 1),
+	.has_hardware_gain = true,
+};
+
+static const struct ad4000_chip_info adaq4003_chip_info = {
+	.dev_name = "adaq4003",
+	.chan_spec = AD4000_DIFF_CHANNEL('s', 18, 0),
+	.reg_access_chan_spec = AD4000_DIFF_CHANNEL('s', 18, 1),
+	.has_hardware_gain = true,
+};
+
+struct ad4000_state {
+	struct spi_device *spi;
+	struct gpio_desc *cnv_gpio;
+	struct spi_transfer xfers[2];
+	struct spi_message msg;
+	struct mutex lock; /* Protect read modify write cycle */
+	int vref_mv;
+	enum ad4000_sdi sdi_pin;
+	bool span_comp;
+	u16 gain_milli;
+	int scale_tbl[AD4000_SCALE_OPTIONS][2];
+
+	/*
+	 * DMA (thus cache coherency maintenance) requires the transfer buffers
+	 * to live in their own cache lines.
+	 */
+	struct {
+		union {
+			__be16 sample_buf16;
+			__be32 sample_buf32;
+		} data;
+		s64 timestamp __aligned(8);
+	} scan __aligned(IIO_DMA_MINALIGN);
+	u8 tx_buf[2];
+	u8 rx_buf[2];
+};
+
+static void ad4000_fill_scale_tbl(struct ad4000_state *st,
+				  struct iio_chan_spec const *chan)
+{
+	int val, tmp0, tmp1;
+	int scale_bits;
+	u64 tmp2;
+
+	/*
+	 * ADCs that output two's complement code have one less bit to express
+	 * voltage magnitude.
+	 */
+	if (chan->scan_type.sign == 's')
+		scale_bits = chan->scan_type.realbits - 1;
+	else
+		scale_bits = chan->scan_type.realbits;
+
+	/*
+	 * The gain is stored as a fraction of 1000 and, as we need to
+	 * divide vref_mv by the gain, we invert the gain/1000 fraction.
+	 * Also multiply by an extra MILLI to preserve precision.
+	 * Thus, we have MILLI * MILLI equals MICRO as fraction numerator.
+	 */
+	val = mult_frac(st->vref_mv, MICRO, st->gain_milli);
+
+	/* Would multiply by NANO here but we multiplied by extra MILLI */
+	tmp2 = shift_right((u64)val * MICRO, scale_bits);
+	tmp0 = div_s64_rem(tmp2, NANO, &tmp1);
+
+	/* Store scale for when span compression is disabled */
+	st->scale_tbl[0][0] = tmp0; /* Integer part */
+	st->scale_tbl[0][1] = abs(tmp1); /* Fractional part */
+
+	/* Store scale for when span compression is enabled */
+	st->scale_tbl[1][0] = tmp0;
+
+	/* The integer part is always zero so don't bother to divide it. */
+	if (chan->differential)
+		st->scale_tbl[1][1] = DIV_ROUND_CLOSEST(abs(tmp1) * 4, 5);
+	else
+		st->scale_tbl[1][1] = DIV_ROUND_CLOSEST(abs(tmp1) * 9, 10);
+}
+
+static int ad4000_write_reg(struct ad4000_state *st, uint8_t val)
+{
+	st->tx_buf[0] = AD4000_WRITE_COMMAND;
+	st->tx_buf[1] = val;
+	return spi_write(st->spi, st->tx_buf, ARRAY_SIZE(st->tx_buf));
+}
+
+static int ad4000_read_reg(struct ad4000_state *st, unsigned int *val)
+{
+	struct spi_transfer t = {
+		.tx_buf = st->tx_buf,
+		.rx_buf = st->rx_buf,
+		.len = 2,
+	};
+	int ret;
+
+	st->tx_buf[0] = AD4000_READ_COMMAND;
+	ret = spi_sync_transfer(st->spi, &t, 1);
+	if (ret < 0)
+		return ret;
+
+	*val = st->rx_buf[1];
+	return ret;
+}
+
+static int ad4000_convert_and_acquire(struct ad4000_state *st)
+{
+	int ret;
+
+	/*
+	 * In 4-wire mode, the CNV line is held high for the entire conversion
+	 * and acquisition process. In other modes, the CNV GPIO is optional
+	 * and, if provided, replaces controller CS. If CNV GPIO is not defined
+	 * gpiod_set_value_cansleep() has no effect.
+	 */
+	gpiod_set_value_cansleep(st->cnv_gpio, 1);
+	ret = spi_sync(st->spi, &st->msg);
+	gpiod_set_value_cansleep(st->cnv_gpio, 0);
+
+	return ret;
+}
+
+static int ad4000_single_conversion(struct iio_dev *indio_dev,
+				    const struct iio_chan_spec *chan, int *val)
+{
+	struct ad4000_state *st = iio_priv(indio_dev);
+	u32 sample;
+	int ret;
+
+	ret = ad4000_convert_and_acquire(st);
+	if (ret < 0)
+		return ret;
+
+	if (chan->scan_type.storagebits > 16)
+		sample = be32_to_cpu(st->scan.data.sample_buf32);
+	else
+		sample = be16_to_cpu(st->scan.data.sample_buf16);
+
+	sample >>= chan->scan_type.shift;
+
+	if (chan->scan_type.sign == 's')
+		*val = sign_extend32(sample, chan->scan_type.realbits - 1);
+
+	return IIO_VAL_INT;
+}
+
+static int ad4000_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan, int *val,
+			   int *val2, long info)
+{
+	struct ad4000_state *st = iio_priv(indio_dev);
+
+	switch (info) {
+	case IIO_CHAN_INFO_RAW:
+		iio_device_claim_direct_scoped(return -EBUSY, indio_dev)
+			return ad4000_single_conversion(indio_dev, chan, val);
+		unreachable();
+	case IIO_CHAN_INFO_SCALE:
+		*val = st->scale_tbl[st->span_comp][0];
+		*val2 = st->scale_tbl[st->span_comp][1];
+		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_OFFSET:
+		*val = 0;
+		if (st->span_comp)
+			*val = mult_frac(st->vref_mv, 1, 10);
+
+		return IIO_VAL_INT;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int ad4000_read_avail(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     const int **vals, int *type, int *length,
+			     long info)
+{
+	struct ad4000_state *st = iio_priv(indio_dev);
+
+	switch (info) {
+	case IIO_CHAN_INFO_SCALE:
+		*vals = (int *)st->scale_tbl;
+		*length = AD4000_SCALE_OPTIONS * 2;
+		*type = IIO_VAL_INT_PLUS_NANO;
+		return IIO_AVAIL_LIST;
+	default:
+		return -EINVAL;
+	}
+}
+
+static int ad4000_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;
+	default:
+		return IIO_VAL_INT_PLUS_MICRO;
+	}
+}
+
+static int ad4000_write_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan, int val, int val2,
+			    long mask)
+{
+	struct ad4000_state *st = iio_priv(indio_dev);
+	unsigned int reg_val;
+	bool span_comp_en;
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
+			guard(mutex)(&st->lock);
+
+			ret = ad4000_read_reg(st, &reg_val);
+			if (ret < 0)
+				return ret;
+
+			span_comp_en = val2 == st->scale_tbl[1][1];
+			reg_val &= ~AD4000_CFG_SPAN_COMP;
+			reg_val |= FIELD_PREP(AD4000_CFG_SPAN_COMP, span_comp_en);
+
+			ret = ad4000_write_reg(st, reg_val);
+			if (ret < 0)
+				return ret;
+
+			st->span_comp = span_comp_en;
+			return 0;
+		}
+		unreachable();
+	default:
+		return -EINVAL;
+	}
+}
+
+static irqreturn_t ad4000_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct ad4000_state *st = iio_priv(indio_dev);
+	int ret;
+
+	ret = ad4000_convert_and_acquire(st);
+	if (ret < 0)
+		goto err_out;
+
+	iio_push_to_buffers_with_timestamp(indio_dev, &st->scan, pf->timestamp);
+
+err_out:
+	iio_trigger_notify_done(indio_dev->trig);
+	return IRQ_HANDLED;
+}
+
+static const struct iio_info ad4000_reg_access_info = {
+	.read_raw = &ad4000_read_raw,
+	.read_avail = &ad4000_read_avail,
+	.write_raw = &ad4000_write_raw,
+	.write_raw_get_fmt = &ad4000_write_raw_get_fmt,
+};
+
+static const struct iio_info ad4000_info = {
+	.read_raw = &ad4000_read_raw,
+};
+
+/*
+ * This executes a data sample transfer for when the device connections are
+ * in "3-wire" mode, selected when the adi,sdi-pin device tree property is
+ * absent or set to "high". In this connection mode, the ADC SDI pin is
+ * connected to MOSI or to VIO and ADC CNV pin is connected either to a SPI
+ * controller CS or to a GPIO.
+ * AD4000 series of devices initiate conversions on the rising edge of CNV pin.
+ *
+ * If the CNV pin is connected to an SPI controller CS line (which is by default
+ * active low), the ADC readings would have a latency (delay) of one read.
+ * Moreover, since we also do ADC sampling for filling the buffer on triggered
+ * buffer mode, the timestamps of buffer readings would be disarranged.
+ * To prevent the read latency and reduce the time discrepancy between the
+ * sample read request and the time of actual sampling by the ADC, do a
+ * preparatory transfer to pulse the CS/CNV line.
+ */
+static int ad4000_prepare_3wire_mode_message(struct ad4000_state *st,
+					     const struct iio_chan_spec *chan)
+{
+	unsigned int cnv_pulse_time = AD4000_TCONV_NS;
+	struct spi_transfer *xfers = st->xfers;
+
+	xfers[0].cs_change = 1;
+	xfers[0].cs_change_delay.value = cnv_pulse_time;
+	xfers[0].cs_change_delay.unit = SPI_DELAY_UNIT_NSECS;
+
+	xfers[1].rx_buf = &st->scan.data;
+	xfers[1].len = BITS_TO_BYTES(chan->scan_type.storagebits);
+	xfers[1].delay.value = AD4000_TQUIET2_NS;
+	xfers[1].delay.unit = SPI_DELAY_UNIT_NSECS;
+
+	spi_message_init_with_transfers(&st->msg, st->xfers, 2);
+
+	return devm_spi_optimize_message(&st->spi->dev, st->spi, &st->msg);
+}
+
+/*
+ * This executes a data sample transfer for when the device connections are
+ * in "4-wire" mode, selected when the adi,sdi-pin device tree property is
+ * set to "cs". In this connection mode, the controller CS pin is connected to
+ * ADC SDI pin and a GPIO is connected to ADC CNV pin.
+ * The GPIO connected to ADC CNV pin is set outside of the SPI transfer.
+ */
+static int ad4000_prepare_4wire_mode_message(struct ad4000_state *st,
+					     const struct iio_chan_spec *chan)
+{
+	unsigned int cnv_to_sdi_time = AD4000_TCONV_NS;
+	struct spi_transfer *xfers = st->xfers;
+
+	/*
+	 * Dummy transfer to cause enough delay between CNV going high and SDI
+	 * going low.
+	 */
+	xfers[0].cs_off = 1;
+	xfers[0].delay.value = cnv_to_sdi_time;
+	xfers[0].delay.unit = SPI_DELAY_UNIT_NSECS;
+
+	xfers[1].rx_buf = &st->scan.data;
+	xfers[1].len = BITS_TO_BYTES(chan->scan_type.storagebits);
+
+	spi_message_init_with_transfers(&st->msg, st->xfers, 2);
+
+	return devm_spi_optimize_message(&st->spi->dev, st->spi, &st->msg);
+}
+
+static int ad4000_config(struct ad4000_state *st)
+{
+	unsigned int reg_val = AD4000_CONFIG_REG_DEFAULT;
+
+	if (device_property_present(&st->spi->dev, "adi,high-z-input"))
+		reg_val |= FIELD_PREP(AD4000_CFG_HIGHZ, 1);
+
+	return ad4000_write_reg(st, reg_val);
+}
+
+static int ad4000_probe(struct spi_device *spi)
+{
+	const struct ad4000_chip_info *chip;
+	struct device *dev = &spi->dev;
+	struct iio_dev *indio_dev;
+	struct ad4000_state *st;
+	int gain_idx, ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	chip = spi_get_device_match_data(spi);
+	if (!chip)
+		return -EINVAL;
+
+	st = iio_priv(indio_dev);
+	st->spi = spi;
+
+	ret = devm_regulator_bulk_get_enable(dev, ARRAY_SIZE(ad4000_power_supplies),
+					     ad4000_power_supplies);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to enable power supplies\n");
+
+	ret = devm_regulator_get_enable_read_voltage(dev, "ref");
+	if (ret < 0)
+		return dev_err_probe(dev, ret,
+				     "Failed to get ref regulator reference\n");
+	st->vref_mv = ret / 1000;
+
+	st->cnv_gpio = devm_gpiod_get_optional(dev, "cnv", GPIOD_OUT_HIGH);
+	if (IS_ERR(st->cnv_gpio))
+		return dev_err_probe(dev, PTR_ERR(st->cnv_gpio),
+				     "Failed to get CNV GPIO");
+
+	ret = device_property_match_property_string(dev, "adi,sdi-pin",
+						    ad4000_sdi_pin,
+						    ARRAY_SIZE(ad4000_sdi_pin));
+	if (ret < 0 && ret != -EINVAL)
+		return dev_err_probe(dev, ret,
+				     "getting adi,sdi-pin property failed\n");
+
+	/* Default to usual SPI connections if pin properties are not present */
+	st->sdi_pin = ret == -EINVAL ? AD4000_SDI_MOSI : ret;
+	switch (st->sdi_pin) {
+	case AD4000_SDI_MOSI:
+		indio_dev->info = &ad4000_reg_access_info;
+		indio_dev->channels = &chip->reg_access_chan_spec;
+
+		/*
+		 * In "3-wire mode", the ADC SDI line must be kept high when
+		 * data is not being clocked out of the controller.
+		 * Request the SPI controller to make MOSI idle high.
+		 */
+		spi->mode |= SPI_MOSI_IDLE_HIGH;
+		ret = spi_setup(spi);
+		if (ret < 0)
+			return ret;
+
+		ret = ad4000_prepare_3wire_mode_message(st, indio_dev->channels);
+		if (ret)
+			return ret;
+
+		ret = ad4000_config(st);
+		if (ret < 0)
+			return dev_err_probe(dev, ret, "Failed to config device\n");
+
+		break;
+	case AD4000_SDI_VIO:
+		indio_dev->info = &ad4000_info;
+		indio_dev->channels = &chip->chan_spec;
+		ret = ad4000_prepare_3wire_mode_message(st, indio_dev->channels);
+		if (ret)
+			return ret;
+
+		break;
+	case AD4000_SDI_CS:
+		indio_dev->info = &ad4000_info;
+		indio_dev->channels = &chip->chan_spec;
+		ret = ad4000_prepare_4wire_mode_message(st, indio_dev->channels);
+		if (ret)
+			return ret;
+
+		break;
+	case AD4000_SDI_GND:
+		return dev_err_probe(dev, -EPROTONOSUPPORT,
+				     "Unsupported connection mode\n");
+
+	default:
+		return dev_err_probe(dev, -EINVAL, "Unrecognized connection mode\n");
+	}
+
+	indio_dev->name = chip->dev_name;
+	indio_dev->num_channels = 1;
+
+	devm_mutex_init(dev, &st->lock);
+
+	st->gain_milli = 1000;
+	if (chip->has_hardware_gain) {
+		ret = device_property_read_u16(dev, "adi,gain-milli",
+					       &st->gain_milli);
+		if (!ret) {
+			/* Match gain value from dt to one of supported gains */
+			gain_idx = find_closest(st->gain_milli, ad4000_gains,
+						ARRAY_SIZE(ad4000_gains));
+			st->gain_milli = ad4000_gains[gain_idx];
+		} else {
+			return dev_err_probe(dev, ret,
+					     "Failed to read gain property\n");
+		}
+	}
+
+	ad4000_fill_scale_tbl(st, indio_dev->channels);
+
+	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+					      &iio_pollfunc_store_time,
+					      &ad4000_trigger_handler, NULL);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct spi_device_id ad4000_id[] = {
+	{ "ad4000", (kernel_ulong_t)&ad4000_chip_info },
+	{ "ad4001", (kernel_ulong_t)&ad4001_chip_info },
+	{ "ad4002", (kernel_ulong_t)&ad4002_chip_info },
+	{ "ad4003", (kernel_ulong_t)&ad4003_chip_info },
+	{ "ad4004", (kernel_ulong_t)&ad4004_chip_info },
+	{ "ad4005", (kernel_ulong_t)&ad4005_chip_info },
+	{ "ad4006", (kernel_ulong_t)&ad4006_chip_info },
+	{ "ad4007", (kernel_ulong_t)&ad4007_chip_info },
+	{ "ad4008", (kernel_ulong_t)&ad4008_chip_info },
+	{ "ad4010", (kernel_ulong_t)&ad4010_chip_info },
+	{ "ad4011", (kernel_ulong_t)&ad4011_chip_info },
+	{ "ad4020", (kernel_ulong_t)&ad4020_chip_info },
+	{ "ad4021", (kernel_ulong_t)&ad4021_chip_info },
+	{ "ad4022", (kernel_ulong_t)&ad4022_chip_info },
+	{ "adaq4001", (kernel_ulong_t)&adaq4001_chip_info },
+	{ "adaq4003", (kernel_ulong_t)&adaq4003_chip_info },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, ad4000_id);
+
+static const struct of_device_id ad4000_of_match[] = {
+	{ .compatible = "adi,ad4000", .data = &ad4000_chip_info },
+	{ .compatible = "adi,ad4001", .data = &ad4001_chip_info },
+	{ .compatible = "adi,ad4002", .data = &ad4002_chip_info },
+	{ .compatible = "adi,ad4003", .data = &ad4003_chip_info },
+	{ .compatible = "adi,ad4004", .data = &ad4004_chip_info },
+	{ .compatible = "adi,ad4005", .data = &ad4005_chip_info },
+	{ .compatible = "adi,ad4006", .data = &ad4006_chip_info },
+	{ .compatible = "adi,ad4007", .data = &ad4007_chip_info },
+	{ .compatible = "adi,ad4008", .data = &ad4008_chip_info },
+	{ .compatible = "adi,ad4010", .data = &ad4010_chip_info },
+	{ .compatible = "adi,ad4011", .data = &ad4011_chip_info },
+	{ .compatible = "adi,ad4020", .data = &ad4020_chip_info },
+	{ .compatible = "adi,ad4021", .data = &ad4021_chip_info },
+	{ .compatible = "adi,ad4022", .data = &ad4022_chip_info },
+	{ .compatible = "adi,adaq4001", .data = &adaq4001_chip_info },
+	{ .compatible = "adi,adaq4003", .data = &adaq4003_chip_info },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ad4000_of_match);
+
+static struct spi_driver ad4000_driver = {
+	.driver = {
+		.name   = "ad4000",
+		.of_match_table = ad4000_of_match,
+	},
+	.probe          = ad4000_probe,
+	.id_table       = ad4000_id,
+};
+module_spi_driver(ad4000_driver);
+
+MODULE_AUTHOR("Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Analog Devices AD4000 ADC driver");
+MODULE_LICENSE("GPL");
-- 
2.43.0