[PATCH v3 1/2] hwmon: (adm1275): Allow setting shunt reg value

[Guenter Roeck]

On Wed, Oct 17, 2018 at 03:26:39PM -0700, Kun Yi wrote:
> The ADM series of hotswap controllers support extending
> the current measurement range by using a sensing resistor
> value other than the typical 1 mOhm. For example, using a 0.5 mOhm
> sensing resistor doubles the maximal current can be measured.
> 
> Current driver assumes a shunt resistor value of 1 mOhm in calculation,
> meaning for other resistor values, hwmon will report scaled
> current/power measurements. This patch parses device tree parameter
> "shunt-resistor-micro-ohms", if there is one.
> 
> Signed-off-by: Kun Yi <kunyi at google.com>

Applied to hwmon-next.

Thanks,
Guenter

> ---
> Changes in v3:
> - splitted hwmon and device tree binding patches
> 
>  Documentation/hwmon/adm1275   |  3 +++
>  drivers/hwmon/pmbus/adm1275.c | 15 +++++++++++++--
>  2 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/hwmon/adm1275 b/Documentation/hwmon/adm1275
> index 39033538eb03..5e277b0d91ce 100644
> --- a/Documentation/hwmon/adm1275
> +++ b/Documentation/hwmon/adm1275
> @@ -58,6 +58,9 @@ The ADM1075, unlike many other PMBus devices, does not support internal voltage
>  or current scaling. Reported voltages, currents, and power are raw measurements,
>  and will typically have to be scaled.
>  
> +The shunt value in micro-ohms can be set via device tree at compile-time. Please
> +refer to the Documentation/devicetree/bindings/hwmon/adm1275.txt for bindings
> +if the device tree is used.
>  
>  Platform data support
>  ---------------------
> diff --git a/drivers/hwmon/pmbus/adm1275.c b/drivers/hwmon/pmbus/adm1275.c
> index 13600fa79e7f..f569372c9204 100644
> --- a/drivers/hwmon/pmbus/adm1275.c
> +++ b/drivers/hwmon/pmbus/adm1275.c
> @@ -373,6 +373,7 @@ static int adm1275_probe(struct i2c_client *client,
>  	const struct coefficients *coefficients;
>  	int vindex = -1, voindex = -1, cindex = -1, pindex = -1;
>  	int tindex = -1;
> +	u32 shunt;
>  
>  	if (!i2c_check_functionality(client->adapter,
>  				     I2C_FUNC_SMBUS_READ_BYTE_DATA
> @@ -421,6 +422,13 @@ static int adm1275_probe(struct i2c_client *client,
>  	if (!data)
>  		return -ENOMEM;
>  
> +	if (of_property_read_u32(client->dev.of_node,
> +				 "shunt-resistor-micro-ohms", &shunt))
> +		shunt = 1000; /* 1 mOhm if not set via DT */
> +
> +	if (shunt == 0)
> +		return -EINVAL;
> +
>  	data->id = mid->driver_data;
>  
>  	info = &data->info;
> @@ -654,12 +662,15 @@ static int adm1275_probe(struct i2c_client *client,
>  		info->R[PSC_VOLTAGE_OUT] = coefficients[voindex].R;
>  	}
>  	if (cindex >= 0) {
> -		info->m[PSC_CURRENT_OUT] = coefficients[cindex].m;
> +		/* Scale current with sense resistor value */
> +		info->m[PSC_CURRENT_OUT] =
> +			coefficients[cindex].m * shunt / 1000;
>  		info->b[PSC_CURRENT_OUT] = coefficients[cindex].b;
>  		info->R[PSC_CURRENT_OUT] = coefficients[cindex].R;
>  	}
>  	if (pindex >= 0) {
> -		info->m[PSC_POWER] = coefficients[pindex].m;
> +		info->m[PSC_POWER] =
> +			coefficients[pindex].m * shunt / 1000;
>  		info->b[PSC_POWER] = coefficients[pindex].b;
>  		info->R[PSC_POWER] = coefficients[pindex].R;
>  	}