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) This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394 Signed-off-by: Maciej Purski <m.purski@xxxxxxxxxxx> --- Changes in v2: - rebase on top of the latest next - remove a redundant variable - power_lsb_uW - fix comments --- drivers/iio/adc/ina2xx-adc.c | 58 +++++++++++++++++++++++--------------------- 1 file changed, 31 insertions(+), 27 deletions(-) diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c index ddf8781..3e4972f 100644 --- a/drivers/iio/adc/ina2xx-adc.c +++ b/drivers/iio/adc/ina2xx-adc.c @@ -124,11 +124,11 @@ enum ina2xx_ids { ina219, ina226 }; struct ina2xx_config { u16 config_default; - int calibration_factor; + int calibration_value; int shunt_voltage_lsb; /* nV */ int bus_voltage_shift; /* position of lsb */ int bus_voltage_lsb; /* uV */ - int power_lsb; /* uW */ + int power_lsb_factor; enum ina2xx_ids chip_id; }; @@ -138,6 +138,7 @@ struct ina2xx_chip_info { const struct ina2xx_config *config; struct mutex state_lock; unsigned int shunt_resistor_uohm; + unsigned int current_lsb_uA; int avg; int int_time_vbus; /* Bus voltage integration time uS */ int int_time_vshunt; /* Shunt voltage integration time uS */ @@ -149,20 +150,20 @@ struct ina2xx_chip_info { static const struct ina2xx_config ina2xx_config[] = { [ina219] = { .config_default = INA219_CONFIG_DEFAULT, - .calibration_factor = 40960000, + .calibration_value = 4096, .shunt_voltage_lsb = 10000, .bus_voltage_shift = INA219_BUS_VOLTAGE_SHIFT, .bus_voltage_lsb = 4000, - .power_lsb = 20000, + .power_lsb_factor = 20, .chip_id = ina219, }, [ina226] = { .config_default = INA226_CONFIG_DEFAULT, - .calibration_factor = 5120000, + .calibration_value = 2048, .shunt_voltage_lsb = 2500, .bus_voltage_shift = 0, .bus_voltage_lsb = 1250, - .power_lsb = 25000, + .power_lsb_factor = 25, .chip_id = ina226, }, }; @@ -229,14 +230,16 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev, case INA2XX_POWER: /* processed (mW) = raw*lsb (uW) / 1000 */ - *val = chip->config->power_lsb; + *val = chip->config->power_lsb_factor * + chip->current_lsb_uA; *val2 = 1000; return IIO_VAL_FRACTIONAL; case INA2XX_CURRENT: - /* processed (mA) = raw (mA) */ - *val = 1; - return IIO_VAL_INT; + /* processed (mA) = raw*lsb (uA) / 1000 */ + *val = chip->current_lsb_uA; + *val2 = 1000; + return IIO_VAL_FRACTIONAL; } case IIO_CHAN_INFO_HARDWAREGAIN: @@ -541,28 +544,34 @@ static ssize_t ina2xx_allow_async_readout_store(struct device *dev, } /* - * Set current LSB to 1mA, shunt is in uOhms - * (equation 13 in datasheet). We hardcode a Current_LSB - * of 1.0 x10-3. The only remaining parameter is RShunt. - * There is no need to expose the CALIBRATION register - * to the user for now. But we need to reset this register - * if the user updates RShunt after driver init, e.g upon - * reading an EEPROM/Probe-type value. + * Calibration register is set to the best value, which eliminates + * truncation errors on calculating current register in hardware. + * According to datasheet (INA 226: eq. 3, INA219: eq. 4) the best values + * are 2048 for ina226 and 4096 for ina219. They are hardcoded as + * calibration_value. */ static int ina2xx_set_calibration(struct ina2xx_chip_info *chip) { - u16 regval = DIV_ROUND_CLOSEST(chip->config->calibration_factor, - chip->shunt_resistor_uohm); - - return regmap_write(chip->regmap, INA2XX_CALIBRATION, regval); + return regmap_write(chip->regmap, INA2XX_CALIBRATION, + chip->config->calibration_value); } +/* + * 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 set_shunt_resistor(struct ina2xx_chip_info *chip, unsigned int val) { - if (val <= 0 || val > chip->config->calibration_factor) + unsigned int dividend = DIV_ROUND_CLOSEST(1000000000, + chip->config->shunt_div); + + if (val <= 0 || val > dividend) return -EINVAL; chip->shunt_resistor_uohm = val; + chip->current_lsb_uA = DIV_ROUND_CLOSEST(dividend, val); return 0; } @@ -592,11 +601,6 @@ static ssize_t ina2xx_shunt_resistor_store(struct device *dev, if (ret) return ret; - /* Update the Calibration register */ - ret = ina2xx_set_calibration(chip); - if (ret) - return ret; - return len; } -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
