Re: [PATCH v3 3/3] iio: dac: ad5766: add driver support for AD5766

[Jonathan Cameron]

On Tue, 8 Dec 2020 15:19:57 +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.
> 
> Link: https://www.analog.com/media/en/technical-documentation/data-sheets/ad5766-5767.pdf
> 
> Signed-off-by: Cristian Pop <cristian.pop@xxxxxxxxxx>

I'm not sure if Andy's review crossed with this, but there are a few questions
outstanding there I think.

A few minor comments in here, but mostly stuff following on from the
comments on patches 1 and 2.

Thanks,

Jonathan

> ---
>  Changelog in v3:
> 	- Add ABI doc
> 	- Add build files
> 	- Fix build, define local macro "IIO_ENUM_AVAILABLE_SHARED"
> 	- Better description for "lock" variable
> 	- Use "put_unaligned_xx16"a
> 	- Rename to: "_ad5766_spi_write" and "_ad5766_spi_read" from 
> 	  "_ad5766_spi_write" and "_ad5766_spi_read"
> 
>  drivers/iio/dac/Kconfig  |  10 +
>  drivers/iio/dac/Makefile |   1 +
>  drivers/iio/dac/ad5766.c | 766 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 777 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..3c634d63a6db
> --- /dev/null
> +++ b/drivers/iio/dac/ad5766.c
> @@ -0,0 +1,766 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Analog Devices AD5766, AD5767
> + * Digital to Analog Converters driver
> + *
> + * Copyright 2019-2020 Analog Devices Inc.
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +#include <linux/iio/iio.h>
> +#include <linux/bitfield.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(x)		GENMASK(((2 * x) + 1), (2 * x))
> +#define AD5766_DITHER_SCALE_MASK(x)		AD5766_DITHER_SOURCE_MASK(x)
> +
> +#define AD5766_CMD_NOP_MUX_OUT			0x00
> +#define AD5766_CMD_SDO_CNTRL			0x01
> +#define AD5766_CMD_WR_IN_REG(x)			(0x10 | ((x) & 0xF))
> +#define AD5766_CMD_WR_DAC_REG(x)		(0x20 | ((x) & 0xF))
> +#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) & 0xF))
> +#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
> +
> +#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,
> +	AD5766_VOLTAGE_RANGE_MAX,
> +};
> +
> +/**
> + * 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_PWR,
> +	AD5766_DITHER_INVERT
> +};
> +
> +/*
> + * External dither signal can be composed with the DAC output, if activated.
> + * The dither signals are applied to the N0 and N1 input pins.
> + * Dither source for each of the channel can be selected by writing to
> + * "dither_source",a 32 bit variable and two bits are used for each of the 16
> + * channels: 0: NO_DITHER, 1: N0, 2: N1.
> + * This variable holds available dither source strings.
> + */
> +static const char * const ad5766_dither_sources[] = {
> +	"NO_DITHER",
> +	"N0",
> +	"N1",
> +};
> +
> +/*
> + * Dither signal can also be scaled.
> + * Available dither scale strings coresponding to "dither_scale" field in
> + * "struct ad5766_state".
> + * "dither_scale" is a 32 bit variable and two bits are used for each of the 16
> + * channels: 0: NO_SCALING, 1: 75%_SCALING, 2: 50%_SCALING, 3: 25%_SCALING.
> + */
> +static const char * const ad5766_dither_scales[] = {
> +	"NO_SCALING",
> +	"75%_SCALING",
> +	"50%_SCALING",
> +	"25%_SCALING",

See ABI docs discussion.

> +};
> +
> +/**
> + * 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
> + * @cached_offset:	Cached range coresponding to the selected offset
> + * @dither_power_ctrl:	Power-down 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 3 possible sources:
> + *			0: No dither, 1: N0, 2: N1
> + *			Two bits are used for each channel
> + * @dither_scale:	Selects between 4 possible scales:
> + *			0: No scale, 1: 75%, 2: 50%, 3: 25%
> + *			Two bits are used for each channel
> + * @scale_avail:	Scale available table
> + * @offset_avail:	Offest available table
> + * @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;
> +	enum ad5766_voltage_range	cached_offset;
> +	u16		dither_power_ctrl;
> +	u16		dither_invert;
> +	u32		dither_source;
> +	u32		dither_scale;
> +	int		scale_avail[AD5766_VOLTAGE_RANGE_MAX][2];
> +	int		offset_avail[AD5766_VOLTAGE_RANGE_MAX][2];
> +	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] = {
> +		.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 = 0;
> +
> +	if (st->gpio_reset) {
> +		gpiod_set_value_cansleep(st->gpio_reset, 0);
> +		ndelay(100); /* t_reset >= 100ns */
> +		gpiod_set_value_cansleep(st->gpio_reset, 1);
> +	} 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_default_setup(struct ad5766_state *st,
> +	enum ad5766_voltage_range range)
> +{
> +	int ret;
> +	uint16_t val;
> +
> +	/* Always issue a software reset before writing to the span register. */
> +	ret = ad5766_reset(st);
> +	if (ret)
> +		return ret;
> +
> +	ret = __ad5766_spi_write(st, AD5766_CMD_SPAN_REG, range);
> +	if (ret)
> +		return ret;
> +
> +	st->crt_range = range;
> +	st->cached_offset = range;
> +
> +	st->dither_power_ctrl = 0;
> +	ret = __ad5766_spi_write(st, AD5766_CMD_WR_PWR_DITHER,
> +			     st->dither_power_ctrl);
> +	if (ret)
> +		return ret;
> +
> +	st->dither_source = 0;
> +	val = FIELD_GET(AD5766_LOWER_WORD_SPI_MASK, st->dither_source);
> +	ret = __ad5766_spi_write(st, AD5766_CMD_DITHER_SIG_1,
> +			  st->dither_source & 0xFFFF);
> +	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);
> +	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 0;
> +}
> +
> +static int ad5766_set_offset(struct ad5766_state *st, int val, int val2)
> +{
> +	int i;
> +	s32 (*tbl)[AD5766_VOLTAGE_RANGE_MAX][2] = &(st->offset_avail);
> +
> +	for (i = 0; i < AD5766_VOLTAGE_RANGE_MAX; i++) {
> +		if ((*tbl)[i][0] == val && (*tbl)[i][1] == val2) {
> +			st->cached_offset = i;
> +			return 0;
> +		}
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int ad5766_set_scale(struct ad5766_state *st, int val, int val2)
> +{
> +	int i;
> +	enum ad5766_voltage_range offset_idx = st->cached_offset;
> +	s32 (*offset_tbl)[AD5766_VOLTAGE_RANGE_MAX][2] = &(st->offset_avail);
> +	s32 (*scale_tbl)[AD5766_VOLTAGE_RANGE_MAX][2] = &(st->scale_avail);
> +
> +	for (i = 0; i < AD5766_VOLTAGE_RANGE_MAX; i++) {
> +		if ((*scale_tbl)[i][0] != val || (*scale_tbl)[i][1] != val2)
> +			continue;
> +
> +		if ((*offset_tbl)[i][0] != (*offset_tbl)[offset_idx][0] ||
> +			(*offset_tbl)[i][1] != (*offset_tbl)[offset_idx][1])
> +			continue;
> +
> +		return ad5766_default_setup(st, i);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int ad5766_read_avail(struct iio_dev *indio_dev,
> +				 struct iio_chan_spec const *chan,
> +				 const int **vals, int *type, int *length,
> +				 long mask)
> +{
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SCALE:
> +		*vals = (const int *)st->scale_avail;
> +		*type = IIO_VAL_INT_PLUS_MICRO;
> +		/* Values are stored in a 2D matrix  */
> +		*length = AD5766_VOLTAGE_RANGE_MAX * 2;
> +
> +		return IIO_AVAIL_LIST;
> +	case IIO_CHAN_INFO_OFFSET:
> +		*vals = (const int *)st->offset_avail;
> +		*type = IIO_VAL_INT_PLUS_MICRO;
> +		/* Values are stored in a 2D matrix  */
> +		*length = AD5766_VOLTAGE_RANGE_MAX * 2;
> +
> +		return IIO_AVAIL_LIST;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int ad5766_read_raw(struct iio_dev *indio_dev,
> +			   struct iio_chan_spec const *chan,
> +			   int *val,
> +			   int *val2,
> +			   long m)
> +{
> +	int ret;
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +
> +	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_SCALE:
> +		*val = st->scale_avail[st->crt_range][0];
> +		*val2 = st->scale_avail[st->crt_range][1];
> +
> +		return IIO_VAL_INT_PLUS_MICRO;
> +
> +	case IIO_CHAN_INFO_OFFSET:
> +		*val = st->offset_avail[st->crt_range][0];
> +		*val2 = st->offset_avail[st->crt_range][1];
> +
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	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)
> +{
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +
> +	switch (info) {
> +	case IIO_CHAN_INFO_RAW:
> +	{
> +		const int max_val = (1 << chan->scan_type.realbits);
> +
> +		if (val >= max_val || val < 0)
> +			return -EINVAL;
> +		val <<= chan->scan_type.shift;
> +		return ad5766_write(indio_dev, chan->address, val);
> +	}
> +	case IIO_CHAN_INFO_OFFSET:
> +		return ad5766_set_offset(st, val, val2);
> +	case IIO_CHAN_INFO_SCALE:
> +		return ad5766_set_scale(st, val, val2);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info ad5766_info = {
> +	.read_raw = ad5766_read_raw,
> +	.write_raw = ad5766_write_raw,
> +	.read_avail = ad5766_read_avail,
> +};
> +
> +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);
> +
> +	return (source >> chan->channel * 2);
> +}
> +
> +static int ad5766_set_dither_source(struct iio_dev *dev,
> +			  const struct iio_chan_spec *chan,
> +			  unsigned int mode)
> +{
> +	int ret;
> +	struct ad5766_state *st = iio_priv(dev);
> +	uint16_t val;
> +
> +	st->dither_source &= ~AD5766_DITHER_SOURCE_MASK(chan->channel);
> +	st->dither_source |= (mode << (chan->channel * 2));
> +
> +	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 const struct iio_enum ad5766_dither_source_enum = {
> +	.items = ad5766_dither_sources,
> +	.num_items = ARRAY_SIZE(ad5766_dither_sources),
> +	.set = ad5766_set_dither_source,
> +	.get = ad5766_get_dither_source,
> +};
> +
> +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 |= (scale << (chan->channel * 2));
> +
> +	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)
> +{
> +	int ret;
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +
> +	switch ((u32)private) {
> +	case AD5766_DITHER_PWR:
> +		return sprintf(buf, "%u\n", 0x01 &
> +			       ~(st->dither_power_ctrl >> chan->channel));
> +		break;
> +	case AD5766_DITHER_INVERT:
> +		return sprintf(buf, "%u\n", 0x01 &
> +			       (st->dither_invert >> chan->channel));
> +		break;
> +	default:
> +		ret = -EINVAL;

return -EINVAL;
and drop the break + return below.

> +		break;
> +	}
> +
> +	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)
> +{
> +	bool readin;
> +	int ret;
> +	struct ad5766_state *st = iio_priv(indio_dev);
> +
> +	ret = kstrtobool(buf, &readin);
> +	if (ret)
> +		return ret;
> +
> +	switch ((u32)private) {
> +	case AD5766_DITHER_PWR:
> +		ret = kstrtobool(buf, &readin);
> +		if (ret)
> +			break;
> +		readin = !readin;
> +		st->dither_power_ctrl = (st->dither_power_ctrl &
> +					 ~BIT(chan->channel)) |
> +					 (readin << chan->channel);
> +		ret = ad5766_write(indio_dev, AD5766_CMD_WR_PWR_DITHER,
> +			     st->dither_power_ctrl);
> +		break;
> +	case AD5766_DITHER_INVERT:
> +		st->dither_invert = (st->dither_invert &
> +						~BIT(chan->channel)) |
> +						(readin << chan->channel);
> +		ret = ad5766_write(indio_dev, AD5766_CMD_INV_DITHER,
> +				st->dither_power_ctrl);
> +		break;
> +	default:
> +		ret = -EINVAL;
return -EINVAL; here is cleaner.

> +		break;
> +	}
> +
> +	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_pwr", AD5766_DITHER_PWR, IIO_SEPARATE),
> +	_AD5766_CHAN_EXT_INFO("dither_invert", AD5766_DITHER_INVERT,
> +			      IIO_SEPARATE),
> +	IIO_ENUM("dither_source", IIO_SEPARATE, &ad5766_dither_source_enum),
> +	IIO_ENUM_AVAILABLE_SHARED("dither_source",
> +				  IIO_SEPARATE,
> +				  &ad5766_dither_source_enum),
> +	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),				\
> +	.info_mask_shared_by_type_available =				\
> +		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 void ad5766_init_scale_tables(struct ad5766_state *st)
> +{
> +	int i;
> +	s32 denom;
> +	s64 offset;
> +	u64 scale;
> +	u8 realbits = st->chip_info->channels[0].scan_type.realbits;
> +
> +	for (i = 0; i < AD5766_VOLTAGE_RANGE_MAX; i++) {
> +		offset = (1 << realbits) * ad5766_span_tbl[i].min;
> +		denom = ad5766_span_tbl[i].max - ad5766_span_tbl[i].min;
> +		offset = div_s64(offset * 1000000, denom);
> +		st->offset_avail[i][0] = div_s64(offset, 1000000);
> +		div_s64_rem(offset, 1000000, &st->offset_avail[i][1]);
> +
> +		scale = ad5766_span_tbl[i].max - ad5766_span_tbl[i].min;
> +		scale = div_u64((scale * 1000000000), (1 << realbits));
> +		st->scale_avail[i][0] = (int)div_u64(scale, 1000000);
> +		div_s64_rem(scale, 1000000, &st->scale_avail[i][1]);
> +	}
> +}
> +
> +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_HIGH);

It's a not reset signal. Which means that you should treat it as active
low which at least means that when we set it to off we come out of reset
and hence aligns with the naming.

Lots of drivers get this wrong :( Let's not introduce another one.

> +
> +	ad5766_init_scale_tables(st);
> +
> +	ret = ad5766_default_setup(st, AD5766_VOLTAGE_RANGE_M5V_to_5V);
> +	if (ret)
> +		return ret;
> +
> +	return devm_iio_device_register(&spi->dev, indio_dev);
> +}
> +
> +static const struct of_device_id ad5766_dt_match[] = {
> +	{ .compatible = "adi,ad5766" },
> +	{ .compatible = "adi,ad5767" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, ad5766_dt_match);
> +
> +static const struct spi_device_id ad5766_spi_ids[] = {
> +	{ "ad5766", ID_AD5766 },
> +	{ "ad5767", ID_AD5767 },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(spi, ad5766_spi_ids);
> +
> +static struct spi_driver ad5766_driver = {
> +	.driver = {
> +		.name = "ad5766",
> +		.of_match_table = ad5766_dt_match,
> +	},
> +	.probe = ad5766_probe,
> +	.id_table = ad5766_spi_ids,
> +};
> +module_spi_driver(ad5766_driver);
> +
> +MODULE_AUTHOR("Denis-Gabriel Gheorghescu <denis.gheorghescu@xxxxxxxxxx>");
> +MODULE_DESCRIPTION("Analog Devices AD5766/AD5767 DACs");
> +MODULE_LICENSE("GPL v2");