Re: [PATCH v3 3/3] iio: adc: add driver for the MAX34417 Four-Channel High Dynamic Range Power Accumulator

[Andy Shevchenko]

On Tue, Oct 13, 2026 at 04:07:13PM +0200, Neil Armstrong wrote:
> The MAX34417 is a specialized current and voltage monitor used to
> determine power consumption of portable systems. The driver support
> getting the channels voltage, average power and accumulated average
> power and energy over an I2C/SMBUS serial interface.
> 
> The MAX34417 datasheet only specified on how to calculate the
> accumulated average power, but with the Sample Per Second rate
> we can easily get accumulated Energy in mJ.
> 
> By default the IIO driver only supports single-shot Voltage
> and Power sensing, but the accumulation can be enabled by
> enabling the Energy IIO channel which then enables the
> Continuous Accumulation Mode.
> 
> The counter is common to all channels, so when reading a single
> channel we will copy all accumulators to registers, so in order
> to permit reading individual channels we must accumulate the
> other channels in the driver when Continuous Accumulation Mode
> is enabled.

...

> +#define MAX34417_MIN_RSENSE		(MILLI)	/* 1 milliOhm */

1 * MILLI

> +#define MAX34417_MAX_RSENSE		(100 * MILLI) /* 100 milliOhm */
> +#define MAX34417_DEFAULT_RSENSE		MAX34417_MIN_RSENSE

I would rather put the exact value here as well.

...

> +struct max34417_data {
> +	struct iio_dev *indio_dev;

> +	struct regmap *regmap;
> +	struct device *dev;

One of them seems redundant (I suppose the 'dev').

> +	struct mutex lock;
> +	u32 input_correction[MAX34417_CHANNEL_COUNT];
> +	const char *input_label[MAX34417_CHANNEL_COUNT];
> +	bool cam_mode;
> +	u64 acc_power[MAX34417_CHANNEL_COUNT];
> +	u32 acc_count[MAX34417_CHANNEL_COUNT];
> +};
> +
> +static const struct regmap_config max34417_regmap_config = {
> +	.reg_bits	= 8,
> +	.val_bits	= 8,
> +	.max_register	= MAX34417_BULK_VOLTAGE_READOUT_REG,

No cache? All registers are volatile?

> +};

...

> +#define MAX34417_CHANNEL(_index, _v_address, _power_address)	\
> +	{							\
> +		.type = IIO_VOLTAGE,				\
> +		.info_mask_separate	= BIT(IIO_CHAN_INFO_RAW) | \
> +					  BIT(IIO_CHAN_INFO_SCALE), \

Instead of broken indentation at the end, use different style for these type of
assignments, like

		.info_mask_separate =
			BIT(IIO_CHAN_INFO_RAW) |		\
			BIT(IIO_CHAN_INFO_SCALE),		\

Also do not use brokenly indented '=', just a space after the field is enough.


> +		.channel = (_index),				\
> +		.address = (_v_address),			\
> +		.indexed = 1,					\
> +	},							\
> +	{							\
> +		.type = IIO_POWER,				\
> +		.info_mask_separate	= BIT(IIO_CHAN_INFO_RAW) | \
> +					  BIT(IIO_CHAN_INFO_AVERAGE_RAW) | \
> +					  BIT(IIO_CHAN_INFO_SCALE), \
> +		.channel = (_index),				\
> +		.address = (_power_address),			\
> +		.indexed = 1,					\
> +	},							\
> +	{							\
> +		.type = IIO_ENERGY,				\
> +		.info_mask_separate	= BIT(IIO_CHAN_INFO_RAW) | \
> +					  BIT(IIO_CHAN_INFO_SCALE), \
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_ENABLE), \
> +		.channel = (_index),				\
> +		.address = (_power_address),			\
> +		.indexed = 1,					\
> +	}

...

> +static int max34417_reset_smm(struct max34417_data *max34417)
> +{
> +	u32 control;
> +	int rc;
> +
> +	rc = regmap_read(max34417->regmap, MAX34417_CONTROL_REG, &control);
> +	if (rc)
> +		return rc;
> +
> +	/* Set SMM=0 to re-init the SMM mode */
> +	control &= ~(MAX34417_CONTROL_SMM);
> +	rc = regmap_write(max34417->regmap, MAX34417_CONTROL_REG, control);
> +	if (rc)
> +		return rc;

regmap_update_bits() / regmap_clear_bits()?

> +	/* Reset accumulators after setting SMM=0 */
> +	rc = regmap_write(max34417->regmap, MAX34417_UPDATE_REG, 1);
> +	if (rc)
> +		return rc;

regmap_set_bits() ?

> +	return 0;
> +}

...

Also check the rest of the code for the similar RMW cases.

...

> +	/*
> +	 * UPDATE commands should be no less than 1msec apart for reliable
> +	 * measurements.
> +	 */
> +	fsleep(1000);

1 * USEC_PER_MSEC

> +	u32 acc_count;
> +	int rc;
> +
> +	rc = max34417_read_acc_count(max34417, &acc_count);
> +	if (rc)
> +		return rc;
> +
> +	for (i = 0; i < MAX34417_CHANNEL_COUNT; ++i) {

'i' is not used outside of the loop AFAICS. Also why pre-increment?

	for (int i = 0; i < MAX34417_CHANNEL_COUNT; i++) {

> +		rc = max34417_read_acc_power(max34417, MAX34417_PWR_ACC_1_REG + i,
> +					     &acc_power);
> +		if (rc)
> +			return rc;
> +
> +		max34417->acc_power[i] += acc_power;
> +		max34417->acc_count[i] += acc_count;
> +	}

...

> +	/* Check for overflow */
> +	rc = max34417_check_ovf(max34417);
> +	if (rc)
> +		return rc;
> +
> +	return 0;

	return ..._check_ovf(...);

...

> +	/* Ignore byte0 */
> +	voltage = get_unaligned_be16(&buf[MAX34417_VOLTAGE_READ_OFFSET]);
> +	voltage >>= 2;

The above comment is odd. Please, clarify, ideally with a reference to
the datasheet table / section / et cetera.

Also can be folded into a single expression:

	voltage = get_unaligned_be16(&buf[MAX34417_VOLTAGE_READ_OFFSET]) >> 2;

...

> +		if (unlikely(acc_count == 0)) {

Why unlikely()? Is this a hot-path? What is the performance effect will it give?

> +			dev_warn(max34417->dev, "unexpected zero accumulator count\n");
> +
> +			*val = 0;
> +			*val2 = 0;
> +
> +			return IIO_VAL_INT_64;
> +		}

...

> +	/*
> +	 * Move the data to the SMBus registers
> +	 */

A single line comment.

...

> +static int max34417_setup_cam_mode(struct max34417_data *max34417, int val)
> +{
> +	u32 control;
> +	int rc, i;
> +
> +	guard(mutex)(&max34417->lock);
> +
> +	rc = regmap_read(max34417->regmap, MAX34417_CONTROL_REG, &control);
> +	if (rc)
> +		return rc;
> +
> +	if (max34417->cam_mode && !val) {
> +		/* SMM and CAM modes should not be enabled at the same time */
> +		control &= ~(MAX34417_CONTROL_CAM | MAX34417_CONTROL_SMM);
> +		rc = regmap_write(max34417->regmap, MAX34417_CONTROL_REG, control);
> +		if (rc)
> +			return rc;
> +
> +		/*
> +		 * If CAM mode must be set, the Control byte must be set to
> +		 * desired values with CAM = 0, then followed by an UPDATE
> +		 */
> +		rc = regmap_write(max34417->regmap, MAX34417_UPDATE_REG, 1);
> +		if (rc)
> +			return rc;
> +	} else if (!max34417->cam_mode && val) {
> +		/*
> +		 * After this, the CAM mode bit can be set and another
> +		 * UPDATE must be sent.
> +		 */
> +		control |= MAX34417_CONTROL_CAM;
> +		/* SMM and CAM modes should not be enabled at the same time */
> +		control &= ~(MAX34417_CONTROL_SMM);
> +		rc = regmap_write(max34417->regmap, MAX34417_CONTROL_REG, control);
> +		if (rc)
> +			return rc;
> +
> +		rc = regmap_write(max34417->regmap, MAX34417_UPDATE_REG, 1);
> +		if (rc)
> +			return rc;
> +
> +		/* Reset counters and accumulators */
> +		for (i = 0; i < MAX34417_CHANNEL_COUNT; ++i) {

		for (int i = 0; i < MAX34417_CHANNEL_COUNT; i++) {

> +			max34417->acc_power[i] = 0;
> +			max34417->acc_count[i] = 0;
> +		}
> +	}
> +
> +	max34417->cam_mode = val;
> +
> +	return 0;
> +}

...

> +static int max34417_read_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     int *val, int *val2, long mask)
> +{
> +	struct max34417_data *max34417 = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		switch (chan->type) {
> +		case IIO_VOLTAGE:
> +			return max34417_read_voltage(max34417, chan, val);
> +		case IIO_POWER:
> +			/* In default mode, we return a single measurement */
> +			if (max34417->cam_mode)
> +				return -EINVAL;
> +
> +			return max34417_read_power(max34417, chan, val, val2);
> +		case IIO_ENERGY:
> +			if (!max34417->cam_mode)
> +				return -EINVAL;
> +
> +			return max34417_read_energy(max34417, chan, val, val2);
> +		default:
> +			return -EINVAL;
> +		}
> +	case IIO_CHAN_INFO_AVERAGE_RAW:
> +		if (chan->type != IIO_POWER)
> +			return -EINVAL;
> +
> +		/* In CAM mode, we return an average measurement */
> +		if (!max34417->cam_mode)
> +			return -EINVAL;
> +
> +		return max34417_read_power(max34417, chan, val, val2);
> +	case IIO_CHAN_INFO_SCALE:
> +		if (chan->type == IIO_VOLTAGE) {
> +			/* Scale to mV */
> +			*val = MAX34417_VOLTAGE_CORRECTION_SCALE * MILLI;
> +			*val2 = MAX34417_VOLTAGE_FULL_SCALE_BITS;
> +
> +			return IIO_VAL_FRACTIONAL_LOG2;
> +		} else if (chan->type == IIO_POWER) {
> +			/*
> +			 * Scale to mW
> +			 * (1000 * (Power Accumulation / Counter) * Correction) / 2^30
> +			 */
> +			*val = max34417->input_correction[chan->channel] * MILLI;

MILLIWATT_PER_WATT

> +			*val2 = MAX34417_PWR_AVG_FULL_SCALE_BITS;
> +
> +			return IIO_VAL_FRACTIONAL_LOG2;
> +		} else if (chan->type == IIO_ENERGY) {
> +			/*
> +			 * Scale to mJ
> +			 * P=(1000 * (Power Accumulation / Counter) * Correction) / 2^30
> +			 * t=(Counter / Samples per Second)
> +			 * E=(P * t)
> +			 * Can be simplified to:
> +			 * (1000 * Power Accumulation * Correction) / (2^30 * SPS)
> +			 * The denominator doesn't fit in 32bit so scale down both terms.
> +			 */
> +			*val = max34417->input_correction[chan->channel];
> +			*val2 = ((u64)(1 << MAX34417_PWR_AVG_FULL_SCALE_BITS) *

Why not BIT_ULL() and drop that casting altogether? Also seems that it becomes
64-bit division. Does it compile on 32-bit?

> +				 MAX34417_FAST_SPS_CAM) / MILLI;
> +
> +			return IIO_VAL_FRACTIONAL;
> +		}
> +
> +		return -EINVAL;
> +	case IIO_CHAN_INFO_ENABLE:
> +		*val = max34417->cam_mode;
> +
> +		return IIO_VAL_INT;
> +	default:
> +		return -EINVAL;
> +	}
> +}

...

> +static int max34417_read_label(struct iio_dev *indio_dev,
> +			       struct iio_chan_spec const *chan,
> +			       char *label)
> +{
> +	struct max34417_data *max34417 = iio_priv(indio_dev);
> +	const char *input_label = max34417->input_label[chan->channel];
> +
> +	if (chan->type == IIO_VOLTAGE) {
> +		if (input_label)
> +			return sysfs_emit(label, "%s-voltage\n", input_label);
> +
> +		return sysfs_emit(label, "channel%d-voltage\n", chan->channel);
> +	}
> +
> +	if (chan->type == IIO_POWER) {
> +		if (input_label)
> +			return sysfs_emit(label, "%s-power\n", input_label);
> +
> +		return sysfs_emit(label, "channel%d-power\n", chan->channel);
> +	}
> +
> +	if (chan->type == IIO_ENERGY) {
> +		if (input_label)
> +			return sysfs_emit(label, "%s-energy\n", input_label);
> +
> +		return sysfs_emit(label, "channel%d-energy\n", chan->channel);
> +	}
> +
> +	return 0;
> +}

This can be simplified, right?

	if (input_label) {
		switch (chan->type) {
		case IIO_VOLTAGE:
			return sysfs_emit(label, "%s-voltage\n", input_label);
		...
		default:
			return 0;
		}
	}

	switch (chan->type) {
	case IIO_VOLTAGE:
		return sysfs_emit(label, "channel%d-voltage\n", chan->channel);
	...
	default:
		return 0;
	}

...

> +	mutex_init(&max34417->lock);

Why not devm_mutex_init()?

...

> +	/* Set default input correction for all channels */
> +	for (i = 0; i < MAX34417_CHANNEL_COUNT; ++i)

	for (int i = 0; i < MAX34417_CHANNEL_COUNT; i++)

> +		max34417->input_correction[i] =
> +			max34417_calc_input_correction(MAX34417_DEFAULT_RSENSE);

...

> +		if (fwnode_property_present(node, "shunt-resistor-micro-ohms")) {
> +			rc = fwnode_property_read_u32(node, "shunt-resistor-micro-ohms",
> +						      &rsense);

Name the variable with units, rsense_mOhm.

> +			if (rc)
> +				return dev_err_probe(dev, rc,
> +						"failure reading shunt property of %pfwP\n",
> +						node);
> +
> +			if (!rsense || rsense < MAX34417_MIN_RSENSE ||
> +			    rsense > MAX34417_MAX_RSENSE)

Please, make it logically split

			// also == 0 is okay for the actual values
			// (which have not a semantic of pointer or error)
			if (rsense == 0 ||
			    rsense < MAX34417_MIN_RSENSE || rsense > MAX34417_MAX_RSENSE)

> +				return dev_err_probe(dev, -EINVAL,
> +						     "invalid shunt value %d of %pfwP\n",
> +						     rsense, node);
> +
> +			max34417->input_correction[index] =
> +				max34417_calc_input_correction(rsense);
> +		}
> +	}

-- 
With Best Regards,
Andy Shevchenko