Re: [PATCH v4 2/4] iio: adc: ad4691: add initial driver for AD4691 family

[Nuno Sá]

Hi Radu,

minor comments on top of what was said already,

On Fri, 2026-03-20 at 13:03 +0200, Radu Sabau via B4 Relay wrote:
> From: Radu Sabau <radu.sabau@xxxxxxxxxx>
> 
> Add support for the Analog Devices AD4691 family of high-speed,
> low-power multichannel SAR ADCs: AD4691 (16-ch, 500 kSPS),
> AD4692 (16-ch, 1 MSPS), AD4693 (8-ch, 500 kSPS) and
> AD4694 (8-ch, 1 MSPS).
> 
> The driver implements a custom regmap layer over raw SPI to handle the
> device's mixed 1/2/3/4-byte register widths and uses the standard IIO
> read_raw/write_raw interface for single-channel reads.
> 
> The chip idles in Autonomous Mode so that single-shot read_raw can use
> the internal oscillator without disturbing the hardware configuration.
> 
> Three voltage supply domains are managed: avdd (required), vio, and a
> reference supply on either the REF pin (ref-supply, external buffer)
> or the REFIN pin (refin-supply, uses the on-chip reference buffer;
> REFBUF_EN is set accordingly). Hardware reset is performed via
> the reset controller framework; a software reset through SPI_CONFIG_A
> is used as fallback when no hardware reset is available.
> 
> Accumulator channel masking for single-shot reads uses ACC_MASK_REG via
> an ADDR_DESCENDING SPI write, which covers both mask bytes in a single
> 16-bit transfer.
> 
> Signed-off-by: Radu Sabau <radu.sabau@xxxxxxxxxx>
> ---
>  MAINTAINERS              |   1 +
>  drivers/iio/adc/Kconfig  |  11 +
>  drivers/iio/adc/Makefile |   1 +
>  drivers/iio/adc/ad4691.c | 686 +++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 699 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 438ca850fa1c..24e4502b8292 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1490,6 +1490,7 @@ L:	linux-iio@xxxxxxxxxxxxxxx
>  S:	Supported
>  W:	https://ez.analog.com/linux-software-drivers
>  F:	Documentation/devicetree/bindings/iio/adc/adi,ad4691.yaml
> +F:	drivers/iio/adc/ad4691.c
>  

...

> 
> +
> +struct ad4691_state {
> +	const struct ad4691_chip_info	*info;
> +	struct regmap			*regmap;
> +	int				vref_uV;
> +	bool				refbuf_en;
> +	bool				ldo_en;
> +	/*
> +	 * Synchronize access to members of the driver state, and ensure
> +	 * atomicity of consecutive SPI operations.
> +	 */
> +	struct mutex			lock;
> +};

I would not use tabs and align all the members. Makes thinks harder in the future if
an update is needed. I would just use a simple space.

> +
> +static int ad4691_reg_read(void *context, unsigned int reg, unsigned int *val)
> +{
> +	struct spi_device *spi = context;
> +	u8 tx[2], rx[4];
> +	int ret;
> +
> +	put_unaligned_be16(0x8000 | reg, tx);
> +
> +	switch (reg) {
> +	case 0 ... AD4691_OSC_FREQ_REG:
> +	case AD4691_SPARE_CONTROL ... AD4691_ACC_SAT_OVR_REG(15):
> +		ret = spi_write_then_read(spi, tx, 2, rx, 1);
> +		if (ret)
> +			return ret;
> +		*val = rx[0];
> +		return 0;
> +	case AD4691_STD_SEQ_CONFIG:
> +	case AD4691_AVG_IN(0) ... AD4691_AVG_IN(15):
> +		ret = spi_write_then_read(spi, tx, 2, rx, 2);
> +		if (ret)
> +			return ret;
> +		*val = get_unaligned_be16(rx);
> +		return 0;
> +	case AD4691_AVG_STS_IN(0) ... AD4691_AVG_STS_IN(15):
> +	case AD4691_ACC_IN(0) ... AD4691_ACC_IN(15):
> +		ret = spi_write_then_read(spi, tx, 2, rx, 3);
> +		if (ret)
> +			return ret;
> +		*val = get_unaligned_be24(rx);
> +		return 0;
> +	case AD4691_ACC_STS_DATA(0) ... AD4691_ACC_STS_DATA(15):
> +		ret = spi_write_then_read(spi, tx, 2, rx, 4);
> +		if (ret)
> +			return ret;
> +		*val = get_unaligned_be32(rx);
> +		return 0;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int ad4691_reg_write(void *context, unsigned int reg, unsigned int val)
> +{
> +	struct spi_device *spi = context;
> +	u8 tx[4];
> +
> +	put_unaligned_be16(reg, tx);
> +
> +	switch (reg) {
> +	case 0 ... AD4691_OSC_FREQ_REG:
> +	case AD4691_SPARE_CONTROL ... AD4691_ACC_MASK_REG - 1:
> +	case AD4691_ACC_MASK_REG + 1 ... AD4691_GPIO_MODE2_REG:
> +		if (val > 0xFF)
> +			return -EINVAL;
> +		tx[2] = val;
> +		return spi_write_then_read(spi, tx, 3, NULL, 0);
> +	case AD4691_ACC_MASK_REG:
> +	case AD4691_STD_SEQ_CONFIG:
> +		if (val > 0xFFFF)
> +			return -EINVAL;
> +		put_unaligned_be16(val, &tx[2]);
> +		return spi_write_then_read(spi, tx, 4, NULL, 0);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static bool ad4691_volatile_reg(struct device *dev, unsigned int reg)
> +{
> +	switch (reg) {
> +	case AD4691_STATUS_REG:
> +	case AD4691_CLAMP_STATUS1_REG:
> +	case AD4691_CLAMP_STATUS2_REG:
> +	case AD4691_GPIO_READ:
> +	case AD4691_ACC_STATUS_FULL1_REG ... AD4691_ACC_STATUS_SAT2_REG:
> +	case AD4691_ACC_SAT_OVR_REG(0) ... AD4691_ACC_SAT_OVR_REG(15):
> +	case AD4691_AVG_IN(0) ... AD4691_AVG_IN(15):
> +	case AD4691_AVG_STS_IN(0) ... AD4691_AVG_STS_IN(15):
> +	case AD4691_ACC_IN(0) ... AD4691_ACC_IN(15):
> +	case AD4691_ACC_STS_DATA(0) ... AD4691_ACC_STS_DATA(15):
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
> +static bool ad4691_readable_reg(struct device *dev, unsigned int reg)
> +{
> +	switch (reg) {
> +	case 0 ... AD4691_OSC_FREQ_REG:
> +	case AD4691_SPARE_CONTROL ... AD4691_ACC_SAT_OVR_REG(15):
> +	case AD4691_STD_SEQ_CONFIG:
> +	case AD4691_AVG_IN(0) ... AD4691_AVG_IN(15):
> +	case AD4691_AVG_STS_IN(0) ... AD4691_AVG_STS_IN(15):
> +	case AD4691_ACC_IN(0) ... AD4691_ACC_IN(15):
> +	case AD4691_ACC_STS_DATA(0) ... AD4691_ACC_STS_DATA(15):
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
> +static bool ad4691_writeable_reg(struct device *dev, unsigned int reg)
> +{
> +	switch (reg) {
> +	case 0 ... AD4691_OSC_FREQ_REG:
> +	case AD4691_STD_SEQ_CONFIG:
> +	case AD4691_SPARE_CONTROL ... AD4691_GPIO_MODE2_REG:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
> +static const struct regmap_config ad4691_regmap_config = {
> +	.reg_bits = 16,
> +	.val_bits = 32,
> +	.reg_read = ad4691_reg_read,
> +	.reg_write = ad4691_reg_write,
> +	.volatile_reg = ad4691_volatile_reg,
> +	.readable_reg = ad4691_readable_reg,
> +	.writeable_reg = ad4691_writeable_reg,
> +	.max_register = AD4691_ACC_STS_DATA(15),
> +	.cache_type = REGCACHE_MAPLE,
> +};
> +
> +static int ad4691_get_sampling_freq(struct ad4691_state *st, int *val)
> +{
> +	unsigned int reg_val;
> +	int ret;
> +
> +	ret = regmap_read(st->regmap, AD4691_OSC_FREQ_REG, &reg_val);
> +	if (ret)
> +		return ret;
> +
> +	*val = ad4691_osc_freqs[FIELD_GET(AD4691_OSC_FREQ_MASK, reg_val)];
> +	return IIO_VAL_INT;
> +}
> +
> +static int ad4691_set_sampling_freq(struct iio_dev *indio_dev, int freq)
> +{
> +	struct ad4691_state *st = iio_priv(indio_dev);
> +	unsigned int start = (st->info->max_rate == HZ_PER_MHZ) ? 0 : 1;
> +	unsigned int i;
> +
> +	IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
> +	if (IIO_DEV_ACQUIRE_FAILED(claim))
> +		return -EBUSY;
> +
> +	for (i = start; i < ARRAY_SIZE(ad4691_osc_freqs); i++) {
> +		if ((int)ad4691_osc_freqs[i] == freq)

maybe just make the array signed.

> +			return regmap_update_bits(st->regmap, AD4691_OSC_FREQ_REG,
> +						  AD4691_OSC_FREQ_MASK, i);
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static int ad4691_read_avail(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     const int **vals, int *type,
> +			     int *length, long mask)
> +{
> +	struct ad4691_state *st = iio_priv(indio_dev);
> +	unsigned int start = (st->info->max_rate == HZ_PER_MHZ) ? 0 : 1;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		*vals = (const int *)&ad4691_osc_freqs[start];
> +		*type = IIO_VAL_INT;
> +		*length = ARRAY_SIZE(ad4691_osc_freqs) - start;
> +		return IIO_AVAIL_LIST;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int ad4691_single_shot_read(struct iio_dev *indio_dev,
> +				   struct iio_chan_spec const *chan, int *val)
> +{
> +	struct ad4691_state *st = iio_priv(indio_dev);
> +	unsigned int reg_val;
> +	int ret;
> +
> +	guard(mutex)(&st->lock);
> +
> +	/*
> +	 * Use AUTONOMOUS mode for single-shot reads. The chip always
> +	 * operates in AUTONOMOUS mode in this driver revision.
> +	 */
> +	ret = regmap_write(st->regmap, AD4691_STATE_RESET_REG,
> +			   AD4691_STATE_RESET_ALL);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(st->regmap, AD4691_STD_SEQ_CONFIG,
> +			   BIT(chan->channel));
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(st->regmap, AD4691_ACC_MASK_REG,
> +			   (u16)~BIT(chan->channel));
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_read(st->regmap, AD4691_OSC_FREQ_REG, &reg_val);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_write(st->regmap, AD4691_OSC_EN_REG, 1);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Wait for at least 2 internal oscillator periods for the
> +	 * conversion to complete.
> +	 */
> +	fsleep(DIV_ROUND_UP(2 * USEC_PER_SEC,
> +			    ad4691_osc_freqs[FIELD_GET(AD4691_OSC_FREQ_MASK,
> +						       reg_val)]));
> +
> +	ret = regmap_write(st->regmap, AD4691_OSC_EN_REG, 0);
> +	if (ret)
> +		return ret;
> +
> +	ret = regmap_read(st->regmap, AD4691_AVG_IN(chan->channel), &reg_val);
> +	if (ret)
> +		return ret;
> +
> +	*val = reg_val;
> +
> +	ret = regmap_write(st->regmap, AD4691_STATE_RESET_REG, AD4691_STATE_RESET_ALL);
> +	if (ret)
> +		return ret;
> +
> +	return IIO_VAL_INT;
> +}
> +
> +static int ad4691_read_raw(struct iio_dev *indio_dev,
> +			   struct iio_chan_spec const *chan, int *val,
> +			   int *val2, long info)
> +{
> +	struct ad4691_state *st = iio_priv(indio_dev);
> +
> +	switch (info) {
> +	case IIO_CHAN_INFO_RAW: {
> +		IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
> +
nit: I would drop the extra new line. The check below is related to the
above.

> +		if (IIO_DEV_ACQUIRE_FAILED(claim))
> +			return -EBUSY;
> +
> +		return ad4691_single_shot_read(indio_dev, chan, val);
> +	}
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return ad4691_get_sampling_freq(st, val);
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = st->vref_uV / (MICRO / MILLI);
> +		*val2 = chan->scan_type.realbits;
> +		return IIO_VAL_FRACTIONAL_LOG2;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int ad4691_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val, int val2, long mask)
> +{
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return ad4691_set_sampling_freq(indio_dev, val);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int ad4691_reg_access(struct iio_dev *indio_dev, unsigned int reg,
> +			     unsigned int writeval, unsigned int *readval)
> +{
> +	struct ad4691_state *st = iio_priv(indio_dev);
> +
> +	guard(mutex)(&st->lock);
> +
> +	if (readval)
> +		return regmap_read(st->regmap, reg, readval);
> +
> +	return regmap_write(st->regmap, reg, writeval);
> +}
> +
> +static const struct iio_info ad4691_info = {
> +	.read_raw = &ad4691_read_raw,
> +	.write_raw = &ad4691_write_raw,
> +	.read_avail = &ad4691_read_avail,
> +	.debugfs_reg_access = &ad4691_reg_access,
> +};
> +
> +static int ad4691_regulator_setup(struct ad4691_state *st)
> +{
> +	struct device *dev = regmap_get_device(st->regmap);
> +	int ret;
> +
> +	ret = devm_regulator_get_enable(dev, "avdd");
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to get and enable AVDD\n");
> +
> +	ret = devm_regulator_get_enable(dev, "ldo-in");
> +	if (ret && ret != -ENODEV)
> +		return dev_err_probe(dev, ret, "Failed to get and enable LDO-IN\n");
> +	st->ldo_en = (ret == -ENODEV);
> +
> +	ret = devm_regulator_get_enable(dev, "vio");
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to get and enable VIO\n");
> +
> +	st->vref_uV = devm_regulator_get_enable_read_voltage(dev, "ref");
> +	if (st->vref_uV >= 0) {
> +		st->refbuf_en = false;
> +	} else if (st->vref_uV == -ENODEV) {
> +		st->vref_uV = devm_regulator_get_enable_read_voltage(dev, "refin");
> +		st->refbuf_en = true;
> +	}
> +	if (st->vref_uV < 0)
> +		return dev_err_probe(dev, st->vref_uV,
> +				     "Failed to get reference supply\n");
> +
> +	if (st->vref_uV < AD4691_VREF_uV_MIN || st->vref_uV > AD4691_VREF_uV_MAX)
> +		return dev_err_probe(dev, -EINVAL,
> +				     "vref(%d) must be in the range [%u...%u]\n",
> +				     st->vref_uV, AD4691_VREF_uV_MIN,
> +				     AD4691_VREF_uV_MAX);
> +
> +	return 0;
> +}
> +
> +static int ad4691_reset(struct ad4691_state *st)
> +{
> +	struct device *dev = regmap_get_device(st->regmap);
> +	struct reset_control *rst;
> +
> +	rst = devm_reset_control_get_optional_exclusive(dev, NULL);
> +	if (IS_ERR(rst))
> +		return dev_err_probe(dev, PTR_ERR(rst), "Failed to get reset\n");
> +
> +	if (!rst)
> +		/* No hardware reset available, fall back to software reset. */
> +		return regmap_write(st->regmap, AD4691_SPI_CONFIG_A_REG,
> +				    AD4691_SW_RESET);
> +
> +	reset_control_assert(rst);

Can't we ask for the reset in the asserted state already?

> +	/* Reset delay required. See datasheet Table 5. */
> +	fsleep(300);
> +	reset_control_deassert(rst);
> +
> +	return 0;
> +}
> +
> +static int ad4691_config(struct ad4691_state *st)
> +{
> +	struct device *dev = regmap_get_device(st->regmap);
> +	enum ad4691_ref_ctrl ref_val;
> +	int ret;
> +
> +	switch (st->vref_uV) {
> +	case AD4691_VREF_uV_MIN ... AD4691_VREF_2P5_uV_MAX:
> +		ref_val = AD4691_VREF_2P5;
> +		break;
> +	case AD4691_VREF_2P5_uV_MAX + 1 ... AD4691_VREF_3P0_uV_MAX:
> +		ref_val = AD4691_VREF_3P0;
> +		break;
> +	case AD4691_VREF_3P0_uV_MAX + 1 ... AD4691_VREF_3P3_uV_MAX:
> +		ref_val = AD4691_VREF_3P3;
> +		break;
> +	case AD4691_VREF_3P3_uV_MAX + 1 ... AD4691_VREF_4P096_uV_MAX:
> +		ref_val = AD4691_VREF_4P096;
> +		break;
> +	case AD4691_VREF_4P096_uV_MAX + 1 ... AD4691_VREF_uV_MAX:
> +		ref_val = AD4691_VREF_5P0;
> +		break;
> +	default:
> +		return dev_err_probe(dev, -EINVAL,
> +				     "Unsupported vref voltage: %d uV\n",
> +				     st->vref_uV);
> +	}
> +
> +	ret = regmap_write(st->regmap, AD4691_REF_CTRL,
> +			   FIELD_PREP(AD4691_REF_CTRL_MASK, ref_val) |
> +			   (st->refbuf_en ? AD4691_REFBUF_EN : 0));
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to write REF_CTRL\n");
> +
> +	ret = regmap_write(st->regmap, AD4691_DEVICE_SETUP,
> +			   st->ldo_en ? AD4691_LDO_EN : 0);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to write DEVICE_SETUP\n");
> +
> +	/*
> +	 * Set the internal oscillator to the highest valid rate for this chip.
> +	 * Index 0 (1 MHz) is valid only for AD4692/AD4694; AD4691/AD4693 start
> +	 * at index 1 (500 kHz).
> +	 */
> +	ret = regmap_write(st->regmap, AD4691_OSC_FREQ_REG,
> +			   (st->info->max_rate == HZ_PER_MHZ) ? 0 : 1);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to write OSC_FREQ\n");
> +
> +	/* Device always operates in AUTONOMOUS mode. */

Kind of obvious from the code. Drop the comment please.


- Nuno Sá