Re: [2/2] hwmon: (ina2xx) Make calibration register value fixed

[Guenter Roeck]

On Wed, Nov 22, 2017 at 04:32:15PM +0100, Maciej Purski wrote:
> Calibration register is used for calculating current register in
> hardware according to datasheet:
> current = shunt_volt * calib_register / 2048 (ina 226)
> current = shunt_volt * calib_register / 4096 (ina 219)
> 
> Fix calib_register value to 2048 for ina226 and 4096 for ina 219 in
> order to avoid truncation error and provide best precision allowed
> by shunt_voltage measurement. Make current scale value follow changes
> of shunt_resistor from sysfs as calib_register value is now fixed.
> 
> Power_lsb value should also follow shunt_resistor changes as stated in
> datasheet:
> power_lsb = 25 * current_lsb (ina 226)
> power_lsb = 20 * current_lsb (ina 219)
> 
> Signed-off-by: Maciej Purski <m.purski@xxxxxxxxxxx>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/ina2xx.c | 87 +++++++++++++++++++++++++++++---------------------
>  1 file changed, 50 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
> index 62e38fa..e362a93 100644
> --- a/drivers/hwmon/ina2xx.c
> +++ b/drivers/hwmon/ina2xx.c
> @@ -95,18 +95,20 @@ enum ina2xx_ids { ina219, ina226 };
>  
>  struct ina2xx_config {
>  	u16 config_default;
> -	int calibration_factor;
> +	int calibration_value;
>  	int registers;
>  	int shunt_div;
>  	int bus_voltage_shift;
>  	int bus_voltage_lsb;	/* uV */
> -	int power_lsb;		/* uW */
> +	int power_lsb_factor;
>  };
>  
>  struct ina2xx_data {
>  	const struct ina2xx_config *config;
>  
>  	long rshunt;
> +	long current_lsb_uA;
> +	long power_lsb_uW;
>  	struct mutex config_lock;
>  	struct regmap *regmap;
>  
> @@ -116,21 +118,21 @@ struct ina2xx_data {
>  static const struct ina2xx_config ina2xx_config[] = {
>  	[ina219] = {
>  		.config_default = INA219_CONFIG_DEFAULT,
> -		.calibration_factor = 40960000,
> +		.calibration_value = 4096,
>  		.registers = INA219_REGISTERS,
>  		.shunt_div = 100,
>  		.bus_voltage_shift = 3,
>  		.bus_voltage_lsb = 4000,
> -		.power_lsb = 20000,
> +		.power_lsb_factor = 20,
>  	},
>  	[ina226] = {
>  		.config_default = INA226_CONFIG_DEFAULT,
> -		.calibration_factor = 5120000,
> +		.calibration_value = 2048,
>  		.registers = INA226_REGISTERS,
>  		.shunt_div = 400,
>  		.bus_voltage_shift = 0,
>  		.bus_voltage_lsb = 1250,
> -		.power_lsb = 25000,
> +		.power_lsb_factor = 25,
>  	},
>  };
>  
> @@ -169,12 +171,16 @@ static u16 ina226_interval_to_reg(int interval)
>  	return INA226_SHIFT_AVG(avg_bits);
>  }
>  
> +/*
> + * Calibration register is set to the best value, which eliminates
> + * truncation errors on calculating current register in hardware.
> + * According to datasheet (eq. 3) the best values are 2048 for
> + * ina226 and 4096 for ina219. They are hardcoded as calibration_value.
> + */
>  static int ina2xx_calibrate(struct ina2xx_data *data)
>  {
> -	u16 val = DIV_ROUND_CLOSEST(data->config->calibration_factor,
> -				    data->rshunt);
> -
> -	return regmap_write(data->regmap, INA2XX_CALIBRATION, val);
> +	return regmap_write(data->regmap, INA2XX_CALIBRATION,
> +			    data->config->calibration_value);
>  }
>  
>  /*
> @@ -187,10 +193,6 @@ static int ina2xx_init(struct ina2xx_data *data)
>  	if (ret < 0)
>  		return ret;
>  
> -	/*
> -	 * Set current LSB to 1mA, shunt is in uOhms
> -	 * (equation 13 in datasheet).
> -	 */
>  	return ina2xx_calibrate(data);
>  }
>  
> @@ -268,15 +270,15 @@ static int ina2xx_get_value(struct ina2xx_data *data, u8 reg,
>  		val = DIV_ROUND_CLOSEST(val, 1000);
>  		break;
>  	case INA2XX_POWER:
> -		val = regval * data->config->power_lsb;
> +		val = regval * data->power_lsb_uW;
>  		break;
>  	case INA2XX_CURRENT:
> -		/* signed register, LSB=1mA (selected), in mA */
> -		val = (s16)regval;
> +		/* signed register, result in mA */
> +		val = regval * data->current_lsb_uA;
> +		val = DIV_ROUND_CLOSEST(val, 1000);
>  		break;
>  	case INA2XX_CALIBRATION:
> -		val = DIV_ROUND_CLOSEST(data->config->calibration_factor,
> -					regval);
> +		val = regval;
>  		break;
>  	default:
>  		/* programmer goofed */
> @@ -304,9 +306,32 @@ static ssize_t ina2xx_show_value(struct device *dev,
>  			ina2xx_get_value(data, attr->index, regval));
>  }
>  
> -static ssize_t ina2xx_set_shunt(struct device *dev,
> -				struct device_attribute *da,
> -				const char *buf, size_t count)
> +/*
> + * In order to keep calibration register value fixed, the product
> + * of current_lsb and shunt_resistor should also be fixed and equal
> + * to shunt_voltage_lsb = 1 / shunt_div multiplied by 10^9 in order
> + * to keep the scale.
> + */
> +static int ina2xx_set_shunt(struct ina2xx_data *data, long val)
> +{
> +	unsigned int dividend = DIV_ROUND_CLOSEST(1000000000,
> +						  data->config->shunt_div);
> +	if (val <= 0 || val > dividend)
> +		return -EINVAL;
> +
> +	mutex_lock(&data->config_lock);
> +	data->rshunt = val;
> +	data->current_lsb_uA = DIV_ROUND_CLOSEST(dividend, val);
> +	data->power_lsb_uW = data->config->power_lsb_factor *
> +			     data->current_lsb_uA;
> +	mutex_unlock(&data->config_lock);
> +
> +	return 0;
> +}
> +
> +static ssize_t ina2xx_store_shunt(struct device *dev,
> +				  struct device_attribute *da,
> +				  const char *buf, size_t count)
>  {
>  	unsigned long val;
>  	int status;
> @@ -316,18 +341,9 @@ static ssize_t ina2xx_set_shunt(struct device *dev,
>  	if (status < 0)
>  		return status;
>  
> -	if (val == 0 ||
> -	    /* Values greater than the calibration factor make no sense. */
> -	    val > data->config->calibration_factor)
> -		return -EINVAL;
> -
> -	mutex_lock(&data->config_lock);
> -	data->rshunt = val;
> -	status = ina2xx_calibrate(data);
> -	mutex_unlock(&data->config_lock);
> +	status = ina2xx_set_shunt(data, val);
>  	if (status < 0)
>  		return status;
> -
>  	return count;
>  }
>  
> @@ -387,7 +403,7 @@ static SENSOR_DEVICE_ATTR(power1_input, S_IRUGO, ina2xx_show_value, NULL,
>  
>  /* shunt resistance */
>  static SENSOR_DEVICE_ATTR(shunt_resistor, S_IRUGO | S_IWUSR,
> -			  ina2xx_show_value, ina2xx_set_shunt,
> +			  ina2xx_show_value, ina2xx_store_shunt,
>  			  INA2XX_CALIBRATION);
>  
>  /* update interval (ina226 only) */
> @@ -448,10 +464,7 @@ static int ina2xx_probe(struct i2c_client *client,
>  			val = INA2XX_RSHUNT_DEFAULT;
>  	}
>  
> -	if (val <= 0 || val > data->config->calibration_factor)
> -		return -ENODEV;
> -
> -	data->rshunt = val;
> +	ina2xx_set_shunt(data, val);
>  
>  	ina2xx_regmap_config.max_register = data->config->registers;
>