Re: [PATCH v5 2/4] hwmon: (pmbus/max20830): add VOUT feedback resistor scaling support

[Guenter Roeck]

On Thu, Jul 30, 2026 at 09:03:34AM +0800, Alexis Czezar Torreno wrote:
> Implement support for external voltage divider scaling using the
> adi,vout-rfb1-ohms and adi,vout-rfb2-ohms device tree properties.
> 
> When the desired output voltage exceeds VREF, a resistor divider
> (RFB1 and RFB2) is used to scale down the feedback voltage. The
> driver reads these resistor values from device tree and applies
> the scaling formula: VOUT_actual = VOUT_measured × (1 + RFB1/RFB2)
> 
> The properties are optional. If not specified, the driver assumes
> no voltage divider is present and reports the raw VOUT reading.
> 
> Signed-off-by: Alexis Czezar Torreno <alexisczezar.torreno@xxxxxxxxxx>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/pmbus/max20830.c | 65 +++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 64 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/pmbus/max20830.c b/drivers/hwmon/pmbus/max20830.c
> index cb2c23672166d641852199ca07eb716924f4f286..ddead72a8db5d6f8491cbfbf356db0f8de64da03 100644
> --- a/drivers/hwmon/pmbus/max20830.c
> +++ b/drivers/hwmon/pmbus/max20830.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/errno.h>
>  #include <linux/i2c.h>
> +#include <linux/math64.h>
>  #include <linux/mod_devicetable.h>
>  #include <linux/module.h>
>  #include <linux/string.h>
> @@ -14,6 +15,56 @@
>  
>  #define MAX20830_IC_DEVICE_ID_LENGTH	9
>  
> +struct max20830_data {
> +	struct pmbus_driver_info info;
> +	u32 vout_rfb1;
> +	u32 vout_rfb2;
> +};
> +
> +/*
> + * MAX20830 only supports READ_VOUT for VOUT monitoring.
> + *
> + * Limit registers (VOUT_OV_WARN_LIMIT, VOUT_OV_FAULT_LIMIT, etc.) are not
> + * supported by this driver and return -ENODATA. This means sysfs attributes
> + * like in1_max, in1_crit, etc. will not be available. Only in1_input (the
> + * scaled output voltage) is supported.
> + *
> + * MAX20830 uses an external resistor divider for voltage sensing:
> + * - VOUT_COMMAND and VOUT_MAX set the reference voltage at the feedback pin
> + * - READ_VOUT reports the feedback voltage, which needs to be scaled for actual
> + *   output voltage
> + *
> + * Scaling formula: vout_actual = vout_fb × (1 + RFB1 / RFB2)
> + *
> + * If regulator support is added in the future, some adjustments are needed to
> + * ensure correct feedback voltages are set.
> + */
> +static int max20830_read_word_data(struct i2c_client *client, int page,
> +				   int phase, int reg)
> +{
> +	const struct pmbus_driver_info *info = pmbus_get_driver_info(client);
> +	const struct max20830_data *data = container_of(info, struct max20830_data, info);
> +	int ret;
> +	u64 temp;
> +
> +	switch (reg) {
> +	case PMBUS_READ_VOUT:
> +		ret = pmbus_read_word_data(client, page, phase, reg);
> +		if (ret < 0)
> +			return ret;
> +
> +		/* Apply voltage divider scaling if resistors are non-zero */
> +		if (data->vout_rfb1 && data->vout_rfb2) {
> +			temp = (u64)data->vout_rfb1 + (u64)data->vout_rfb2;
> +			temp = DIV_ROUND_CLOSEST_ULL((u64)ret * temp, data->vout_rfb2);
> +			ret = clamp_val(temp, 0, 0xFFFF);
> +		}
> +		return ret;
> +	default:
> +		return -ENODATA;
> +	}
> +}
> +
>  static struct pmbus_driver_info max20830_info = {
>  	.pages = 1,
>  	.format[PSC_VOLTAGE_IN] = linear,
> @@ -24,13 +75,25 @@ static struct pmbus_driver_info max20830_info = {
>  		PMBUS_HAVE_TEMP |
>  		PMBUS_HAVE_STATUS_VOUT | PMBUS_HAVE_STATUS_IOUT |
>  		PMBUS_HAVE_STATUS_INPUT | PMBUS_HAVE_STATUS_TEMP,
> +	.read_word_data = max20830_read_word_data,
>  };
>  
>  static int max20830_probe(struct i2c_client *client)
>  {
>  	u8 buf[I2C_SMBUS_BLOCK_MAX + 1] = {};
> +	struct max20830_data *data;
>  	int ret;
>  
> +	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->info = max20830_info;
> +
> +	/* Read optional voltage divider resistor values */
> +	device_property_read_u32(&client->dev, "adi,vout-rfb1-ohms", &data->vout_rfb1);
> +	device_property_read_u32(&client->dev, "adi,vout-rfb2-ohms", &data->vout_rfb2);
> +
>  	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_BLOCK_DATA) &&
>  	    !i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_READ_I2C_BLOCK))
>  		return -ENODEV;
> @@ -78,7 +141,7 @@ static int max20830_probe(struct i2c_client *client)
>  		return dev_err_probe(&client->dev, -ENODEV,
>  				     "Unsupported device: '%s'\n", buf);
>  
> -	return pmbus_do_probe(client, &max20830_info);
> +	return pmbus_do_probe(client, &data->info);
>  }
>  
>  static const struct i2c_device_id max20830_id[] = {