Re: [PATCH v5 3/3] iio: adc: add driver for the MAX34417 Four-Channel High Dynamic Range Power Accumulator

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 02 Nov 2026 15:49:06 +0100
Neil Armstrong <neil.armstrong@linaro.org> 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.
> 
> Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>

The use of the regmap_noinc stuff to deal with the variable
size 'registers' is novel.  Might be worth just adding a little
commentary on that to somewhere. Perhaps the regmap_config as a comment.

Other than that, just a question about why we need the postfixes
for the labels. That seems superfluous.

Thanks,

Jonathan


> diff --git a/drivers/iio/adc/max34417.c b/drivers/iio/adc/max34417.c
> new file mode 100644
> index 000000000000..e679cf142141
> --- /dev/null
> +++ b/drivers/iio/adc/max34417.c

> +
> +static const struct regmap_config max34417_regmap_config = {
> +	.reg_bits	= 8,
> +	.val_bits	= 8,
As noted above. This isn't really true.  You are just use noinc
reads to pretend it is.  Those are normally only used for
fifo registers so I think we should have a comment here talking
about that choice.

It is pretty neat so I'm not against it but it might rather
surprise anyone looking at the datasheet!



> +	.max_register	= MAX34417_BULK_VOLTAGE_READOUT_REG,
> +	.writeable_reg	= max34417_writeable_reg,
> +	.readable_reg	= max34417_readable_reg,
> +	.volatile_reg	= max34417_volatile_reg,
> +	/* No cache since the only non-volatile register is read-only */
> +};



> +
> +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);

Why add the postfix? The channel type will turn up in the file name anyway.
I don't think anything prevents us having the same label for channels of
different types.  Is this a copy of something elsewhere?


> +		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);
Same applies here.  The postfix seems excessive.
> +	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 int max34417_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct max34417_data *max34417;
> +	struct iio_dev *indio_dev;
> +	struct regmap *map;
> +	int rc;
> +
> +	map = devm_regmap_init_i2c(client, &max34417_regmap_config);
> +	if (IS_ERR(map))
> +		return dev_err_probe(dev, PTR_ERR(map), "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 = map;
> +	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_uOhm, index;
> +
> +		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, -ECHRNG, "invalid reg %d of %pfwP\n",
> +					     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",

Don't worry about going a bit longer - stcik to aligning after (
Or.. Maybe use a helper function for the per channel parsing.


> +						node);
> +		}
> +
> +		if (fwnode_property_present(node, "shunt-resistor-micro-ohms")) {
> +			rc = fwnode_property_read_u32(node, "shunt-resistor-micro-ohms",
> +						      &rsense_uOhm);
> +			if (rc)
> +				return dev_err_probe(dev, rc,
> +						"failure reading shunt property of %pfwP\n",
> +						node);
> +
> +			if (rsense_uOhm < MAX34417_MIN_RSENSE ||
> +			    rsense_uOhm > MAX34417_MAX_RSENSE)
> +				return dev_err_probe(dev, -EINVAL,
> +						     "invalid shunt value %d of %pfwP\n",
> +						     rsense_uOhm, node);
> +
> +			max34417->input_correction[index] =
> +				max34417_calc_input_correction(rsense_uOhm);
> +		}
> +	}