Re: [PATCH v4 3/3] iio: adc: add driver for the MAX34417 Four-Channel High Dynamic Range Power Accumulator

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Wed, Oct 28, 2026 at 02:19:06PM +0100, 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, 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		(1 * MILLI) /* 1000 microOhm */
> +#define MAX34417_MAX_RSENSE		(100 * MILLI) /* 100000 microOhm */
> +#define MAX34417_DEFAULT_RSENSE		(1 * MILLI) /* 1000 microOhm */

Add unit suffix. The comment versus MILLI multiplier is quite confusing.
What I read, it's milli-Ohms by value.

...

> +struct max34417_data {
> +	struct iio_dev *indio_dev;
> +	struct regmap *regmap;
> +	struct mutex lock;
> +	u32 input_correction[MAX34417_CHANNEL_COUNT];
> +	const char *input_label[MAX34417_CHANNEL_COUNT];
> +	bool cam_mode;

Don't you have 4-byte gap here in some cases? Can you confirm the layout
with `pahole`? On top you can check binary size by running `bloat-o-meter`.

> +	u64 acc_power[MAX34417_CHANNEL_COUNT];
> +	u64 acc_count[MAX34417_CHANNEL_COUNT];
> +};

...

> +static bool max34417_volatile_reg(struct device *dev, unsigned int reg)
> +{
> +	switch (reg) {
> +	case MAX34417_DID_REG:
> +		return false;
> +	default:
> +	/* MAX34417_CONTROL_REG field OVF is volatile */

Why not add a case instead of a comment?

> +		return true;
> +	}
> +}

...

> +static int max34417_reset_smm(struct max34417_data *max34417)
> +{
> +	int rc;
> +
> +	/* Set SMM=0 to re-init the SMM mode */
> +	rc = regmap_clear_bits(max34417->regmap, MAX34417_CONTROL_REG,
> +			       MAX34417_CONTROL_SMM);

With

	struct regmap *map = max34417->regmap;

this becomes a single line

	rc = regmap_clear_bits(map, MAX34417_CONTROL_REG, MAX34417_CONTROL_SMM);

Use this trick elsewhere where appropriate.

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

...

> +	*val = lower_32_bits(power);
> +	*val2 = upper_32_bits(power);

Have you included wordpart.h?

...

> +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 (input_label) {
> +		switch (chan->type) {
> +		case IIO_VOLTAGE:
> +			return sysfs_emit(label, "%s-voltage\n", input_label);

sysfs.h for sysfs_emit().

> +		case IIO_POWER:
> +			return sysfs_emit(label, "%s-power\n", input_label);
> +		case IIO_ENERGY:
> +			return sysfs_emit(label, "%s-energy\n", input_label);
> +		default:
> +			return 0;
> +		}
> +	}
> +
> +	switch (chan->type) {
> +	case IIO_VOLTAGE:
> +		return sysfs_emit(label, "channel%d-voltage\n", chan->channel);
> +	case IIO_POWER:
> +		return sysfs_emit(label, "channel%d-power\n", chan->channel);
> +	case IIO_ENERGY:
> +		return sysfs_emit(label, "channel%d-energy\n", chan->channel);
> +	default:
> +		return 0;
> +	}
> +}

...

> +static unsigned int max34417_calc_input_correction(u32 rsense_microOhm)

rsense_uOhm is shorter

> +{
> +	/* (100 milliOhm / rsense) * MAX34417_PWR_CORRECTION_SCALE */

Comment in this form is almost useless. Rather explain that we except
the result in the certain units or something like this.

> +	return (MAX34417_MAX_RSENSE * MAX34417_PWR_CORRECTION_SCALE) / rsense_microOhm;
> +}

...

> +static int max34417_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct max34417_data *max34417;
> +	struct iio_dev *indio_dev;
> +	struct regmap *regmap;

*map is shorter

> +	int rc;
> +
> +	regmap = devm_regmap_init_i2c(client, &max34417_regmap_config);
> +	if (IS_ERR(regmap))
> +		return dev_err_probe(dev, PTR_ERR(regmap), "regmap_init failed\n");
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*max34417));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	rc = devm_regulator_get_enable(dev, "vdd");
> +	if (rc)
> +		return dev_err_probe(dev, rc, "failed to get vdd regulator\n");
> +
> +	rc = devm_regulator_get_enable(dev, "vio");
> +	if (rc)
> +		return dev_err_probe(dev, rc, "failed to get vio regulator\n");
> +
> +	max34417 = iio_priv(indio_dev);
> +	max34417->regmap = regmap;
> +	max34417->indio_dev = indio_dev;
> +
> +	rc = devm_mutex_init(dev, &max34417->lock);
> +	if (rc)
> +		return rc;
> +
> +	/* Set default input correction for all channels */
> +	for (int i = 0; i < MAX34417_CHANNEL_COUNT; i++)
> +		max34417->input_correction[i] =
> +			max34417_calc_input_correction(MAX34417_DEFAULT_RSENSE);
> +
> +	device_for_each_child_node_scoped(dev, node) {
> +		u32 rsense_microOhm, index;

rsense_uOhm

> +		rc = fwnode_property_read_u32(node, "reg", &index);
> +		if (rc)
> +			return dev_err_probe(dev, rc, "failure reading reg property of %pfwP\n",
> +					     node);
> +
> +		if (index >= MAX34417_CHANNEL_COUNT)
> +			return dev_err_probe(dev, -EINVAL, "invalid reg %d of %pfwP\n",

-ECHRNG

> +					     index, node);
> +
> +		if (fwnode_property_present(node, "label")) {
> +			rc = fwnode_property_read_string(node, "label",
> +							 &max34417->input_label[index]);
> +			if (rc)
> +				return dev_err_probe(dev, rc,
> +						"failure reading label property of %pfwP\n",
> +						node);
> +		}
> +
> +		if (fwnode_property_present(node, "shunt-resistor-micro-ohms")) {
> +			rc = fwnode_property_read_u32(node, "shunt-resistor-micro-ohms",
> +						      &rsense_microOhm);
> +			if (rc)
> +				return dev_err_probe(dev, rc,
> +						"failure reading shunt property of %pfwP\n",
> +						node);
> +
> +			if (rsense_microOhm < MAX34417_MIN_RSENSE ||
> +			    rsense_microOhm > MAX34417_MAX_RSENSE)
> +				return dev_err_probe(dev, -EINVAL,
> +						     "invalid shunt value %d of %pfwP\n",
> +						     rsense_microOhm, node);
> +
> +			max34417->input_correction[index] =
> +				max34417_calc_input_correction(rsense_microOhm);
> +		}
> +	}
> +
> +	indio_dev->channels = max34417_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(max34417_channels);
> +	indio_dev->name = "max34417";
> +	indio_dev->info = &max34417_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +
> +	/*
> +	 * Reset mode and set accumulator width to Wide
> +	 *
> +	 * The MAX34407 variant could be supported by setting the
> +	 * MAX34417_CONTROL_MODE field to 0 and handling a smaller
> +	 * accumulator width.
> +	 */
> +	rc = regmap_write(max34417->regmap, MAX34417_CONTROL_REG, MAX34417_CONTROL_MODE);

You have local variable for regmap, use it.

> +	if (rc)
> +		return dev_err_probe(dev, rc, "Error writing control register\n");
> +
> +	/* Reset the accumulators */
> +	rc = regmap_write(max34417->regmap, MAX34417_UPDATE_REG, 1);
> +	if (rc)
> +		return rc;
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}

-- 
With Best Regards,
Andy Shevchenko