From a28caa7b8fe19ac2c31b7630772107e0d50ce18e Mon Sep 17 00:00:00 2001 From: Maciej Purski Date: Mon, 18 Dec 2017 09:43:58 +0100 Subject: iio: adc: ina2xx: Make calibration register value fixed MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Stefan Brüns Signed-off-by: Jonathan Cameron Signed-off-by: Greg Kroah-Hartman --- drivers/iio/adc/ina2xx-adc.c | 64 +++++++++++++++++++++++--------------------- 1 file changed, 33 insertions(+), 31 deletions(-) (limited to 'drivers/iio/adc') diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c index 2621a34ee5c6..94d506f0f404 100644 --- a/drivers/iio/adc/ina2xx-adc.c +++ b/drivers/iio/adc/ina2xx-adc.c @@ -124,11 +124,12 @@ 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 */ + /* fixed relation between current and power lsb, uW/uA */ + int power_lsb_factor; enum ina2xx_ids chip_id; }; @@ -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, }, }; @@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev, *val2 = 1000; return IIO_VAL_FRACTIONAL; - case INA2XX_POWER: - /* processed (mW) = raw*lsb (uW) / 1000 */ - *val = chip->config->power_lsb; - *val2 = 1000; + case INA2XX_CURRENT: + /* + * processed (mA) = raw * current_lsb (mA) + * current_lsb (mA) = shunt_voltage_lsb (nV) / + * shunt_resistor (uOhm) + */ + *val = chip->config->shunt_voltage_lsb; + *val2 = chip->shunt_resistor_uohm; return IIO_VAL_FRACTIONAL; - case INA2XX_CURRENT: - /* processed (mA) = raw (mA) */ - *val = 1; - return IIO_VAL_INT; + case INA2XX_POWER: + /* + * processed (mW) = raw * power_lsb (mW) + * power_lsb (mW) = power_lsb_factor (mW/mA) * + * current_lsb (mA) + */ + *val = chip->config->power_lsb_factor * + chip->config->shunt_voltage_lsb; + *val2 = chip->shunt_resistor_uohm; + return IIO_VAL_FRACTIONAL; } case IIO_CHAN_INFO_HARDWAREGAIN: @@ -541,25 +552,21 @@ 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); } static int set_shunt_resistor(struct ina2xx_chip_info *chip, unsigned int val) { - if (val <= 0 || val > chip->config->calibration_factor) + if (val == 0 || val > INT_MAX) return -EINVAL; chip->shunt_resistor_uohm = val; @@ -592,11 +599,6 @@ 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; } -- cgit v1.2.3