Re: [PATCH v4 3/3] iio: dac: ad5766: add driver support for AD5766

[Jonathan Cameron]

On Fri, 18 Dec 2020 19:12:31 +0200
Cristian Pop <cristian.pop@xxxxxxxxxx> wrote:

> The AD5766/AD5767 are 16-channel, 16-bit/12-bit, voltage output dense DACs
> Digital-to-Analog converters.
> 
> This change adds support for these DACs.
> 
> Signed-off-by: Cristian Pop <cristian.pop@xxxxxxxxxx>
Hi Cristian,

The addressing in this device 'interesting'. I'm not sure it can be handled
much better than you have done though.

Otherwise, a few minor bits and pieces inline.

Thanks,

Jonathan


> ---
> Changelog v4:
> 	- Select output range
> 	- Set possible dither source to: 0 - N0 and 1 for N1.
> 	- Better macros usage
> 	- Invert reset logic
> 	- Use GENMASK
> 	- Add/remove some commas
>  drivers/iio/dac/Kconfig  |  10 +
>  drivers/iio/dac/Makefile |   1 +
>  drivers/iio/dac/ad5766.c | 668 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 679 insertions(+)
>  create mode 100644 drivers/iio/dac/ad5766.c
> 
> diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
> index 6f6074a5d3db..cea07b4cced1 100644
> --- a/drivers/iio/dac/Kconfig
> +++ b/drivers/iio/dac/Kconfig
> @@ -189,6 +189,16 @@ config AD5764
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called ad5764.
>  
> +config AD5766
> +	tristate "Analog Devices AD5766/AD5767 DAC driver"
> +	depends on SPI_MASTER
> +	help
> +	  Say yes here to build support for Analog Devices AD5766, AD5767
> +	  Digital to Analog Converter.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called ad5766.
> +
>  config AD5770R
>  	tristate "Analog Devices AD5770R IDAC driver"
>  	depends on SPI_MASTER
> diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
> index 2fc481167724..33e16f14902a 100644
> --- a/drivers/iio/dac/Makefile
> +++ b/drivers/iio/dac/Makefile
> @@ -19,6 +19,7 @@ obj-$(CONFIG_AD5755) += ad5755.o
>  obj-$(CONFIG_AD5755) += ad5758.o
>  obj-$(CONFIG_AD5761) += ad5761.o
>  obj-$(CONFIG_AD5764) += ad5764.o
> +obj-$(CONFIG_AD5766) += ad5766.o
>  obj-$(CONFIG_AD5770R) += ad5770r.o
>  obj-$(CONFIG_AD5791) += ad5791.o
>  obj-$(CONFIG_AD5686) += ad5686.o
> diff --git a/drivers/iio/dac/ad5766.c b/drivers/iio/dac/ad5766.c
> new file mode 100644
> index 000000000000..b7405185f3d8
> --- /dev/null
> +++ b/drivers/iio/dac/ad5766.c
> @@ -0,0 +1,668 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Analog Devices AD5766, AD5767
> + * Digital to Analog Converters driver
> + * Copyright 2019-2020 Analog Devices Inc.
> + */
> +#include <linux/bitfield.h>
> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +#include <linux/unaligned/be_byteshift.h>
> +
> +#define AD5766_UPPER_WORD_SPI_MASK		GENMASK(31, 16)
> +#define AD5766_LOWER_WORD_SPI_MASK		GENMASK(15, 0)
> +#define AD5766_DITHER_SOURCE_MASK(ch)		GENMASK(((2 * ch) + 1), (2 * ch))
> +#define AD5766_DITHER_SOURCE(ch, source)	BIT((ch * 2) + source)
> +#define AD5766_DITHER_SCALE_MASK(x)		AD5766_DITHER_SOURCE_MASK(x)
> +#define AD5766_DITHER_SCALE(ch, scale)		(scale << (ch * 2))
> +#define AD5766_DITHER_ENABLE_MASK(ch)		BIT(ch)
> +#define AD5766_DITHER_ENABLE(ch, state)		((!state) << ch)
> +#define AD5766_DITHER_INVERT_MASK(ch)		BIT(ch)
> +#define AD5766_DITHER_INVERT(ch, state)		(state << ch)
> +
> +#define AD5766_CMD_NOP_MUX_OUT			0x00
> +#define AD5766_CMD_SDO_CNTRL			0x01
> +#define AD5766_CMD_WR_IN_REG(x)			(0x10 | ((x) & GENMASK(3, 0)))
> +#define AD5766_CMD_WR_DAC_REG(x)		(0x20 | ((x) & GENMASK(3, 0)))
> +#define AD5766_CMD_SW_LDAC			0x30
> +#define AD5766_CMD_SPAN_REG			0x40
> +#define AD5766_CMD_WR_PWR_DITHER		0x51
> +#define AD5766_CMD_WR_DAC_REG_ALL		0x60
> +#define AD5766_CMD_SW_FULL_RESET		0x70
> +#define AD5766_CMD_READBACK_REG(x)		(0x80 | ((x) & GENMASK(3, 0)))
> +#define AD5766_CMD_DITHER_SIG_1			0x90
> +#define AD5766_CMD_DITHER_SIG_2			0xA0
> +#define AD5766_CMD_INV_DITHER			0xB0
> +#define AD5766_CMD_DITHER_SCALE_1		0xC0
> +#define AD5766_CMD_DITHER_SCALE_2		0xD0

These addresses struck me as 'unusual' so I went and had a look at the datasheet.
I would separate the definition of C3-C0 and A3-A0 as then it will look a lot
more obvious as we will just have registers 0x0 to 0xD, some of which are banked
with the address bits acting as selector.

However. There are at least 2 special cases where the address bits aren't acting
to specify a banked per output channel register *sigh* so perhaps what you have
is the best we can do.

> +
> +#define AD5766_FULL_RESET_CODE			0x1234
> +
> +enum ad5766_type {
> +	ID_AD5766,
> +	ID_AD5767,
> +};
> +
> +enum ad5766_voltage_range {
> +	AD5766_VOLTAGE_RANGE_M20V_0V,
> +	AD5766_VOLTAGE_RANGE_M16V_to_0V,
> +	AD5766_VOLTAGE_RANGE_M10V_to_0V,
> +	AD5766_VOLTAGE_RANGE_M12V_to_14V,
> +	AD5766_VOLTAGE_RANGE_M16V_to_10V,
> +	AD5766_VOLTAGE_RANGE_M10V_to_6V,
> +	AD5766_VOLTAGE_RANGE_M5V_to_5V,
> +	AD5766_VOLTAGE_RANGE_M10V_to_10V,
> +};
> +
> +/**
> + * struct ad5766_chip_info - chip specific information
> + * @num_channels:	number of channels
> + * @channel:	        channel specification
> + */
> +struct ad5766_chip_info {
> +	unsigned int			num_channels;
> +	const struct iio_chan_spec	*channels;
> +};
> +
> +enum {
> +	AD5766_DITHER_ENABLE,
> +	AD5766_DITHER_INVERT,
> +	AD5766_DITHER_SOURCE,
> +};
> +
> +/*
> + * Dither signal can also be scaled.
> + * Available dither scale strings corresponding to "dither_scale" field in
> + * "struct ad5766_state".
> + */
> +static const char * const ad5766_dither_scales[] = {
> +	"100",
> +	"75",
> +	"50",
> +	"25",
> +};
> +
> +/**
> + * struct ad5766_state - driver instance specific data
> + * @spi:		SPI device
> + * @lock:		Lock used to restrict concurent access to SPI device
> + * @chip_info:		Chip model specific constants
> + * @gpio_reset:		Reset GPIO, used to reset the device
> + * @crt_range:		Current selected output range
> + * @dither_enable:	Power enable bit for each channel dither block (for
> + *			example, D15 = DAC 15,D8 = DAC 8, and D0 = DAC 0)
> + *			0 - Normal operation, 1 - Power down
> + * @dither_invert:	Inverts the dither signal applied to the selected DAC
> + *			outputs
> + * @dither_source:	Selects between 2 possible sources:
> + *			1: N0, 2: N1
> + *			Two bits are used for each channel
> + * @dither_scale:	Two bits are used for each of the 16 channels:
> + *			0: 100% SCALING, 1: 75% SCALING, 2: 50% SCALING,
> + *			3: 25% SCALING.
> + * @data:		SPI transfer buffers
> + */
> +struct ad5766_state {
> +	struct spi_device		*spi;
> +	struct mutex			lock;
> +	const struct ad5766_chip_info	*chip_info;
> +	struct gpio_desc		*gpio_reset;
> +	enum ad5766_voltage_range	crt_range;
> +	u16		dither_enable;
> +	u16		dither_invert;
> +	u32		dither_source;
> +	u32		dither_scale;
> +	union {
> +		u32	d32;
> +		u16	w16[2];
> +		u8	b8[4];
> +	} data[3] ____cacheline_aligned;
> +};
> +
> +struct ad5766_span_tbl {
> +	int		min;
> +	int		max;
> +};
> +
> +static const struct ad5766_span_tbl ad5766_span_tbl[] = {
> +	[AD5766_VOLTAGE_RANGE_M20V_0V] = {
Giving naming you 'could' just assume the min, max element was clear enough
and go with
        [AD5766_VOLTAGE_RANGE_M20V_0V] = {-20, 0}, etc
I don't think there would be any significant loss in readability.

> +		.min = -20,
> +		.max = 0,
> +	},
> +	[AD5766_VOLTAGE_RANGE_M16V_to_0V] = {
> +		.min = -16,
> +		.max = 0,
> +	},
> +	[AD5766_VOLTAGE_RANGE_M10V_to_0V] = {
> +		.min = -10,
> +		.max = 0,
> +	},
> +	[AD5766_VOLTAGE_RANGE_M12V_to_14V] = {
> +		.min = -12,
> +		.max = 14,
> +	},
> +	[AD5766_VOLTAGE_RANGE_M16V_to_10V] = {
> +		.min = -16,
> +		.max = 10,
> +	},
> +	[AD5766_VOLTAGE_RANGE_M10V_to_6V] = {
> +		.min = -10,
> +		.max = 6,
> +	},
> +	[AD5766_VOLTAGE_RANGE_M5V_to_5V] = {
> +		.min = -5,
> +		.max = 5,
> +	},
> +	[AD5766_VOLTAGE_RANGE_M10V_to_10V] = {
> +		.min = -10,
> +		.max = 10,
> +	},
> +};
> +
> +static int __ad5766_spi_read(struct ad5766_state *st, u8 dac, int *val)
> +{
> +	int ret;
> +	struct spi_transfer xfers[] = {
> +		{
> +			.tx_buf = &st->data[0].d32,
> +			.bits_per_word = 8,
> +			.len = 3,
> +			.cs_change = 1,
> +		}, {
> +			.tx_buf = &st->data[1].d32,
> +			.rx_buf = &st->data[2].d32,
> +			.bits_per_word = 8,
> +			.len = 3,
> +		},
> +	};
> +
> +	st->data[0].d32 = AD5766_CMD_READBACK_REG(dac);
> +	st->data[1].d32 = AD5766_CMD_NOP_MUX_OUT;
> +
> +	ret = spi_sync_transfer(st->spi, xfers, ARRAY_SIZE(xfers));
> +	if (ret)
> +		return ret;
> +
> +	*val = st->data[2].w16[1];
> +
> +	return ret;
> +}
> +
> +static int __ad5766_spi_write(struct ad5766_state *st, u8 command, u16 data)
> +{
> +	st->data[0].b8[0] = command;
> +	put_unaligned_be16(data, &st->data[0].b8[1]);
> +
> +	return spi_write(st->spi, &st->data[0].b8[0], 3);
> +}
> +
> +static int ad5766_read(struct iio_dev *indio_dev, u8 dac, int *val)
> +{
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	mutex_lock(&st->lock);
> +	ret = __ad5766_spi_read(st, dac, val);
> +	mutex_unlock(&st->lock);
> +
> +	return ret;
> +}
> +
> +static int ad5766_write(struct iio_dev *indio_dev, u8 dac, u16 data)
> +{
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	mutex_lock(&st->lock);
> +	ret = __ad5766_spi_write(st, AD5766_CMD_WR_DAC_REG(dac), data);
> +	mutex_unlock(&st->lock);
> +
> +	return ret;
> +}
> +
> +static int ad5766_reset(struct ad5766_state *st)
> +{
> +	int ret;
> +
> +	if (st->gpio_reset) {
> +		gpiod_set_value_cansleep(st->gpio_reset, 1);
> +		ndelay(100); /* t_reset >= 100ns */
> +		gpiod_set_value_cansleep(st->gpio_reset, 0);
> +	} else {
> +		ret = __ad5766_spi_write(st, AD5766_CMD_SW_FULL_RESET,
> +					AD5766_FULL_RESET_CODE);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	/*
> +	 * Minimum time between a reset and the subsequent successful write is
> +	 * typically 25 ns
> +	 */
> +	ndelay(25);
> +
> +	return 0;
> +}
> +
> +static int ad5766_read_raw(struct iio_dev *indio_dev,
> +			   struct iio_chan_spec const *chan,
> +			   int *val,
> +			   int *val2,
> +			   long m)
> +{
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (m) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = ad5766_read(indio_dev, chan->address, val);
> +		if (ret)
> +			return ret;
> +
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_OFFSET:
> +		*val = ad5766_span_tbl[st->crt_range].min;
> +
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = ad5766_span_tbl[st->crt_range].max -
> +		       ad5766_span_tbl[st->crt_range].min;
> +		*val2 = st->chip_info->channels[0].scan_type.realbits;
> +
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int ad5766_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val,
> +			    int val2,
> +			    long info)
> +{
> +	switch (info) {
> +	case IIO_CHAN_INFO_RAW:
> +	{
> +		const int max_val = GENMASK(chan->scan_type.realbits - 1, 0);
> +
> +		if (val > max_val || val < 0)
> +			return -EINVAL;
> +		val <<= chan->scan_type.shift;
> +		return ad5766_write(indio_dev, chan->address, val);
> +	}
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info ad5766_info = {
> +	.read_raw = ad5766_read_raw,
> +	.write_raw = ad5766_write_raw,
> +};
> +
> +static int ad5766_get_dither_source(struct iio_dev *dev,
> +				    const struct iio_chan_spec *chan)
> +{
> +	struct ad5766_state *st = iio_priv(dev);
> +	u32 source;
> +
> +	source = st->dither_source & AD5766_DITHER_SOURCE_MASK(chan->channel);
> +	source = source >> (chan->channel * 2);
> +	source -= 1;
> +
> +	return source;
> +}
> +
> +static int ad5766_set_dither_source(struct iio_dev *dev,
> +			  const struct iio_chan_spec *chan,
> +			  unsigned int source)
> +{
> +	struct ad5766_state *st = iio_priv(dev);
> +	uint16_t val;
> +	int ret;
> +
> +	st->dither_source &= ~AD5766_DITHER_SOURCE_MASK(chan->channel);
> +	st->dither_source |= AD5766_DITHER_SOURCE(chan->channel, source);
> +
> +	val = FIELD_GET(AD5766_LOWER_WORD_SPI_MASK, st->dither_source);
> +	ret = ad5766_write(dev, AD5766_CMD_DITHER_SIG_1, val);
> +	if (ret)
> +		return ret;
> +
> +	val = FIELD_GET(AD5766_UPPER_WORD_SPI_MASK, st->dither_source);
> +
> +	return ad5766_write(dev, AD5766_CMD_DITHER_SIG_2, val);
> +}
> +
> +static int ad5766_get_dither_scale(struct iio_dev *dev,
> +				   const struct iio_chan_spec *chan)
> +{
> +	struct ad5766_state *st = iio_priv(dev);
> +	u32 scale;
> +
> +	scale = st->dither_scale & AD5766_DITHER_SCALE_MASK(chan->channel);
> +
> +	return (scale >> (chan->channel * 2));
> +}
> +
> +static int ad5766_set_dither_scale(struct iio_dev *dev,
> +			  const struct iio_chan_spec *chan,
> +			  unsigned int scale)
> +{
> +	int ret;
> +	struct ad5766_state *st = iio_priv(dev);
> +	uint16_t val;
> +
> +	st->dither_scale &= ~AD5766_DITHER_SCALE_MASK(chan->channel);
> +	st->dither_scale |= AD5766_DITHER_SCALE(chan->channel, scale);
> +
> +	val = FIELD_GET(AD5766_LOWER_WORD_SPI_MASK, st->dither_scale);
> +	ret = ad5766_write(dev, AD5766_CMD_DITHER_SCALE_1, val);
> +	if (ret)
> +		return ret;
> +	val = FIELD_GET(AD5766_UPPER_WORD_SPI_MASK, st->dither_scale);
> +
> +	return ad5766_write(dev, AD5766_CMD_DITHER_SCALE_2, val);
> +}
> +
> +static const struct iio_enum ad5766_dither_scale_enum = {
> +	.items = ad5766_dither_scales,
> +	.num_items = ARRAY_SIZE(ad5766_dither_scales),
> +	.set = ad5766_set_dither_scale,
> +	.get = ad5766_get_dither_scale,
> +};
> +
> +static ssize_t ad5766_read_ext(struct iio_dev *indio_dev,
> +			       uintptr_t private,
> +			       const struct iio_chan_spec *chan,
> +			       char *buf)
> +{
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (private) {
> +	case AD5766_DITHER_ENABLE:
> +		return sprintf(buf, "%u\n",
> +			       !(st->dither_enable & BIT(chan->channel)));
> +		break;
> +	case AD5766_DITHER_INVERT:
> +		return sprintf(buf, "%u\n",
> +			       !!(st->dither_invert & BIT(chan->channel)));
> +		break;
> +	case AD5766_DITHER_SOURCE:
> +		return sprintf(buf, "%u\n",
> +			       ad5766_get_dither_source(indio_dev, chan));
> +	default:
> +		return -EINVAL;
> +	}
> +

Can't get here

> +	return ret;
> +}
> +
> +static ssize_t ad5766_write_ext(struct iio_dev *indio_dev,
> +				 uintptr_t private,
> +				 const struct iio_chan_spec *chan,
> +				 const char *buf, size_t len)
> +{
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +	bool readin;
> +	int ret;
> +
> +	ret = kstrtobool(buf, &readin);
> +	if (ret)
> +		return ret;
> +
> +	switch (private) {
> +	case AD5766_DITHER_ENABLE:
> +		st->dither_enable &= ~AD5766_DITHER_ENABLE_MASK(chan->channel);
> +		st->dither_enable |= AD5766_DITHER_ENABLE(chan->channel,
> +							  readin);
> +		ret = ad5766_write(indio_dev, AD5766_CMD_WR_PWR_DITHER,
> +				   st->dither_enable);
> +		break;
> +	case AD5766_DITHER_INVERT:
> +		st->dither_invert &= ~AD5766_DITHER_INVERT_MASK(chan->channel);
> +		st->dither_invert |= AD5766_DITHER_INVERT(chan->channel,
> +							  readin);
> +		ret = ad5766_write(indio_dev, AD5766_CMD_INV_DITHER,
> +				   st->dither_invert);
> +		break;
> +	case AD5766_DITHER_SOURCE:
> +		ret = ad5766_set_dither_source(indio_dev, chan, readin);
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return ret ? ret : len;
> +}
> +
> +#define _AD5766_CHAN_EXT_INFO(_name, _what, _shared) { \
> +	.name = _name, \
> +	.read = ad5766_read_ext, \
> +	.write = ad5766_write_ext, \
> +	.private = _what, \
> +	.shared = _shared, \
> +}
> +
> +#define IIO_ENUM_AVAILABLE_SHARED(_name, _shared, _e) \
> +{ \
> +	.name = (_name "_available"), \
> +	.shared = _shared, \
> +	.read = iio_enum_available_read, \
> +	.private = (uintptr_t)(_e), \
> +}
> +
> +static const struct iio_chan_spec_ext_info ad5766_ext_info[] = {
> +
> +	_AD5766_CHAN_EXT_INFO("dither_enable", AD5766_DITHER_ENABLE,
> +			      IIO_SEPARATE),
> +	_AD5766_CHAN_EXT_INFO("dither_invert", AD5766_DITHER_INVERT,
> +			      IIO_SEPARATE),
> +	_AD5766_CHAN_EXT_INFO("dither_source", AD5766_DITHER_SOURCE,
> +			      IIO_SEPARATE),
> +	IIO_ENUM("dither_scale", IIO_SEPARATE, &ad5766_dither_scale_enum),
> +	IIO_ENUM_AVAILABLE_SHARED("dither_scale",
> +				  IIO_SEPARATE,
> +				  &ad5766_dither_scale_enum),
> +	{}
> +};
> +
> +#define AD576x_CHANNEL(_chan, _bits) {					\
> +	.type = IIO_VOLTAGE,						\
> +	.indexed = 1,							\
> +	.output = 1,							\
> +	.channel = (_chan),						\
> +	.address = (_chan),						\
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),			\
> +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |		\
> +		BIT(IIO_CHAN_INFO_SCALE),				\
> +	.scan_type = {							\
> +		.sign = 'u',						\
> +		.realbits = (_bits),					\
> +		.storagebits = 16,					\
> +		.shift = 16 - (_bits),					\
> +	},								\
> +	.ext_info = ad5766_ext_info,					\
> +}
> +
> +#define DECLARE_AD576x_CHANNELS(_name, _bits)			\
> +const struct iio_chan_spec _name[] = {				\
> +	AD576x_CHANNEL(0, (_bits)),				\
> +	AD576x_CHANNEL(1, (_bits)),				\
> +	AD576x_CHANNEL(2, (_bits)),				\
> +	AD576x_CHANNEL(3, (_bits)),				\
> +	AD576x_CHANNEL(4, (_bits)),				\
> +	AD576x_CHANNEL(5, (_bits)),				\
> +	AD576x_CHANNEL(6, (_bits)),				\
> +	AD576x_CHANNEL(7, (_bits)),				\
> +	AD576x_CHANNEL(8, (_bits)),				\
> +	AD576x_CHANNEL(9, (_bits)),				\
> +	AD576x_CHANNEL(10, (_bits)),				\
> +	AD576x_CHANNEL(11, (_bits)),				\
> +	AD576x_CHANNEL(12, (_bits)),				\
> +	AD576x_CHANNEL(13, (_bits)),				\
> +	AD576x_CHANNEL(14, (_bits)),				\
> +	AD576x_CHANNEL(15, (_bits)),				\
> +}
> +
> +static DECLARE_AD576x_CHANNELS(ad5766_channels, 16);
> +static DECLARE_AD576x_CHANNELS(ad5767_channels, 12);
> +
> +static const struct ad5766_chip_info ad5766_chip_infos[] = {
> +	[ID_AD5766] = {
> +		.num_channels = ARRAY_SIZE(ad5766_channels),
> +		.channels = ad5766_channels,
> +	},
> +	[ID_AD5767] = {
> +		.num_channels = ARRAY_SIZE(ad5767_channels),
> +		.channels = ad5767_channels,
> +	},
> +};
> +
> +static int ad5766_get_output_range(struct ad5766_state *st)
> +{
> +	int i, ret, min, max, tmp[2];
> +
> +	ret = device_property_read_u32_array(&st->spi->dev,
> +					     "output-range",
> +					     tmp, 2);
> +	if (ret)
> +		return ret;
> +
> +	min = tmp[0];
> +	max = tmp[1];
> +	for (i = 0; i < ARRAY_SIZE(ad5766_span_tbl); i++) {
> +		if (ad5766_span_tbl[i].min != min ||
> +		    ad5766_span_tbl[i].max != max)
> +			continue;
> +
> +		st->crt_range = i;
> +
> +		return 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int ad5766_default_setup(struct ad5766_state *st)
> +{
> +	uint16_t val;
> +	int ret, i;
> +
> +	/* Always issue a reset before writing to the span register. */
> +	ret = ad5766_reset(st);
> +	if (ret)
> +		return ret;
> +
> +	ret = ad5766_get_output_range(st);
> +	if (ret)
> +		return ret;
> +
> +	/* Dither power down */
> +	st->dither_enable = GENMASK(15, 0);
> +	ret = __ad5766_spi_write(st, AD5766_CMD_WR_PWR_DITHER,
> +			     st->dither_enable);
> +	if (ret)
> +		return ret;
> +
> +	st->dither_source = 0;
> +	for (i = 0; i < ARRAY_SIZE(ad5766_channels); i++)
> +		st->dither_source |= AD5766_DITHER_SOURCE(i, 0);
> +	val = FIELD_GET(AD5766_LOWER_WORD_SPI_MASK, st->dither_source);
> +	ret = __ad5766_spi_write(st, AD5766_CMD_DITHER_SIG_1, val);
> +	if (ret)
> +		return ret;
> +
> +	val = FIELD_GET(AD5766_UPPER_WORD_SPI_MASK, st->dither_source);
> +	ret = __ad5766_spi_write(st, AD5766_CMD_DITHER_SIG_2, val);
> +	if (ret)
> +		return ret;
> +
> +	st->dither_scale = 0;
> +	val = FIELD_GET(AD5766_LOWER_WORD_SPI_MASK, st->dither_scale);
> +	ret = __ad5766_spi_write(st, AD5766_CMD_DITHER_SCALE_1, val);
> +	if (ret)
> +		return ret;
> +
> +	val = FIELD_GET(AD5766_UPPER_WORD_SPI_MASK, st->dither_scale);

This is a rather unusual use of FIELD_GET to split a value that we then
write to two 16 bit registers. I guess it works, but does feel a bit odd.
If you are happy with it, I guess I can cope with it confusing me.

> +	ret = __ad5766_spi_write(st, AD5766_CMD_DITHER_SCALE_2, val);
> +	if (ret)
> +		return ret;
> +
> +	st->dither_invert = 0;
> +	ret = __ad5766_spi_write(st, AD5766_CMD_INV_DITHER, st->dither_invert);
> +	if (ret)
> +		return ret;
> +
> +	return  __ad5766_spi_write(st, AD5766_CMD_SPAN_REG, st->crt_range);
> +}
> +
> +static int ad5766_probe(struct spi_device *spi)
> +{
> +	enum ad5766_type type;
> +	struct iio_dev *indio_dev;
> +	struct ad5766_state *st;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	st = iio_priv(indio_dev);
> +	mutex_init(&st->lock);
> +
> +	st->spi = spi;
> +	type = spi_get_device_id(spi)->driver_data;
> +	st->chip_info = &ad5766_chip_infos[type];
> +
> +	indio_dev->channels = st->chip_info->channels;
> +	indio_dev->num_channels = st->chip_info->num_channels;
> +	indio_dev->info = &ad5766_info;
> +	indio_dev->dev.parent = &spi->dev;
> +	indio_dev->dev.of_node = spi->dev.of_node;
> +	indio_dev->name = spi_get_device_id(spi)->name;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +
> +	st->gpio_reset = devm_gpiod_get_optional(&st->spi->dev, "reset",
> +						GPIOD_OUT_LOW);

Minor point, but in theory this might return an error code rather than
NULL (which it will return if no gpio was specified). Should probably
handle that.

> +
> +	ret = ad5766_default_setup(st);
> +	if (ret)
> +		return ret;
> +
> +	return devm_iio_device_register(&spi->dev, indio_dev);
> +}
> +
...