Re: [PATCH v1 2/2] iio: adc: add MAX40080 current-sense amplifier driver

[David Lechner]

On 7/3/26 5:29 AM, Stefan Popa wrote:
> The MAX40080 is a bidirectional current-sense amplifier with an
> integrated 12-bit ADC and an I2C/SMBus interface. It measures the
> voltage across an external shunt resistor and the input bus voltage,
> storing the results in an internal FIFO.
> 
> Add a direct-mode IIO driver exposing the current and voltage channels
> with raw, scale and hardware-gain attributes, a configurable

Patch does not implemnt hardware-gain attribute (which is correct,
so just fix the commit message).

> oversampling (digital averaging) ratio, and PEC-protected register
> access. The current scale is derived from the shunt resistor value
> described in the device tree.
> 
> +static int max40080_update_bits(struct max40080_state *st, u8 reg,
> +				u16 mask, u16 val)
> +{
> +	int ret;
> +	int tmp;
> +
> +	guard(mutex)(&st->lock);

Usually we don't want the lock at this level in case anything needs to
update more than one register in an atomic operation.

> +
> +	tmp = i2c_smbus_read_word_data(st->client, reg);
> +	if (tmp < 0)
> +		return tmp;
> +
> +	tmp &= ~mask;
> +	tmp |= val & mask;
> +
> +	ret = i2c_smbus_write_word_data(st->client, reg, tmp);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +

...

> +static int max40080_read_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     int *val,
> +			     int *val2,
> +			     long mask)
> +{
> +	struct max40080_state *st = iio_priv(indio_dev);
> +	unsigned int range;
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		if (chan->type == IIO_CURRENT) {
> +			ret = max40080_get_current(st, val);
> +			if (ret)
> +				return ret;
> +		} else if (chan->type == IIO_VOLTAGE) {
> +			ret = max40080_get_voltage(st, val);
> +			if (ret)
> +				return ret;
> +		}

Se usually use switch statement in IIO instead of else if.

> +
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		if (chan->type == IIO_CURRENT) {
> +			/*
> +			 * The selectable current-sense range is exposed through
> +			 * scale: each RANGE setting has its own precomputed
> +			 * mA-per-code value. Userspace picks the range by writing
> +			 * the matching scale.
> +			 */
> +			ret = max40080_get_range(st, &range);
> +			if (ret)
> +				return ret;
> +
> +			*val = st->current_scale[range][0];
> +			*val2 = st->current_scale[range][1];
> +			return IIO_VAL_INT_PLUS_NANO;
> +		}
> +		/* voltage[mV] = raw * Vref[mV] * buffer_gain / ADC_RES */
> +		*val = MAX40080_INTER_VREF_MV * MAX40080_V_BUFF_GAIN;
> +		*val2 = MAX40080_ADC_RES;
> +		return IIO_VAL_FRACTIONAL;
> +	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> +		ret = max40080_get_oversampling_ratio(st, val);
> +		if (ret)
> +			return ret;
> +		return IIO_VAL_INT;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +

...

> +static int max40080_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct iio_dev *indio_dev;
> +	struct max40080_state *st;
> +	int ret;
> +
> +	if (!i2c_check_functionality(client->adapter,
> +				     I2C_FUNC_SMBUS_WORD_DATA |
> +				     I2C_FUNC_SMBUS_I2C_BLOCK |
> +				     I2C_FUNC_SMBUS_QUICK))
> +		return -EOPNOTSUPP;
> +
> +	client->flags |= I2C_CLIENT_PEC;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	i2c_set_clientdata(client, indio_dev);
> +
> +	st = iio_priv(indio_dev);
> +	st->client = client;
> +
> +	ret = devm_mutex_init(dev, &st->lock);
> +	if (ret)
> +		return ret;
> +
> +	if (device_property_read_u32(dev, "shunt-resistor-micro-ohms",
> +				     &st->shunt_resistor_uohm))
> +		st->shunt_resistor_uohm = 1000000; /* default 1 ohm */
> +
> +	if (!st->shunt_resistor_uohm)
> +		return dev_err_probe(dev, -EINVAL,
> +				     "shunt-resistor-micro-ohms must be non-zero\n");
> +
> +	max40080_calc_current_scale(st);
> +
> +	indio_dev->name = "max40080";
> +	indio_dev->info = &max40080_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = max40080_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(max40080_channels);
> +
> +	/* No averaging by default; configurable at runtime via sysfs. */
> +	ret = max40080_init(st, 1);

Why have a paramter if it is always the same value? Can just move
this comment into the init function and drop the arg.

> +	if (ret)
> +		return ret;
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}
> +
> +static const struct i2c_device_id max40080_i2c_ids[] = {
> +	{ "max40080" },

Include `.name = `

> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, max40080_i2c_ids);
> +