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

[Jonathan Cameron]

On Fri, 20 Mar 2026 13:03:56 +0200
Radu Sabau via B4 Relay <devnull+radu.sabau.analog.com@xxxxxxxxxx> 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>
Hi Radu,

Just a few minor comments from me.
I'd have tweak them whilst applying but looks like you are doing a v5 anyway
for other comments.

Jonathan


> diff --git a/drivers/iio/adc/ad4691.c b/drivers/iio/adc/ad4691.c
> new file mode 100644
> index 000000000000..5e02eb44ca44
> --- /dev/null
> +++ b/drivers/iio/adc/ad4691.c

> +#define AD4691_CHANNEL(ch)						\
> +	{								\
> +		.type = IIO_VOLTAGE,					\
> +		.indexed = 1,						\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW)		\
> +				    | BIT(IIO_CHAN_INFO_SAMP_FREQ),	\
> +		.info_mask_separate_available =				\
> +				      BIT(IIO_CHAN_INFO_SAMP_FREQ),	\
> +		.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SCALE),	\
> +		.channel = ch,						\
> +		.scan_index = ch,					\
> +		.scan_type = {						\
> +			.sign = 'u',					\
> +			.realbits = 16,					\
> +			.storagebits = 16,				\
> +			.shift = 0,					\

Unless there is a reason to need the 0 to act as documentation we normally
assume it's the natural default and don't set it explicitly (let the C
struct initialization rules deal with setting it to 0 for us).

> +		},							\
> +	}


> +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;

Use 1 * HZ_PER_MHZ

May seem pointless but that conversion scale macro on it's own looks
strange with respect to what is it converting.

> +	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)

I would flip this around to reduce the indent of the path for when
we have a match.

		if ((int)ad4691_osc_freqs[i] != freq)
			continue;

		return regmap_update_bits(st->regmap, AD4691_OSC_FREQ_REG,
					  AD4691_OSC_FREQ_MASK, i);


> +			return regmap_update_bits(st->regmap, AD4691_OSC_FREQ_REG,
> +						  AD4691_OSC_FREQ_MASK, i);
> +	}
> +
> +	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)]));

Go long on this line for readability.
			    ad4691_osc_freqs[FIELD_GET(AD4691_OSC_FREQ_MASK, reg_val)]));
Is fine.  The whole 80-100 char range is fine to use if it improves redability and
here I think it does.

> +
> +	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);
> +

I think we should have convention of no blank line here.
The bit above is setting a variable then we are checking it for error.

> +		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_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");

Unless there is an ordering constraint for power supplies, I'd move this up to
just after avdd so the two non optional ones are done together.

> +
> +	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;
> +	}