On Donnerstag, 7. Dezember 2017 13:02:47 CET 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) > > 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; I don't think you need current_lsb_uA, see below ... > 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; .. this is the only place where current_lsb_uA is used ... > + 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); 1st: shunt_div no longer exists, but shunt_voltage_lsb[nV], so this code does not even compile ... This function does two things - range check and calculation of the curren_lsb_uA auxiliary variable. Lets start with the second part: read_raw returns the IIO_VAL_FRACTIONAL val / val2 = current_lsb_uA / 1000 (1) from set_shunt_resistor(...): dividend = 1e9 / shunt_div (2) current_lsb_uA = dividend / shunt_resistor_uohm (3) shunt_div no longer exists, but can be substituted: shunt_div = 1e6 / shunt_voltage_lsb (4) substituting (2), (3) and (4) in (1), we end up with val / val2 = 1e9 / (shunt_div * shunt_resistor_uohm * 1000) => val / val2 = 1e6 / ((1e6 / shunt_voltage_lsb) * shunt_resistor_uohm) => val / val2 = shunt_voltage_lsb / shunt_resistor_uohm => [mA] = [nV] / [uOhm] The auxiliary variable is gone, as are the two DIV_ROUND_CLOSEST calls. Part 2, range check: lower bound is obviously 1 uOhm. The upper bound is only limited by typeof(val2) and typeof(shunt_resistor_uohm), both are ints. so the range check can be simplified to if (val == 0 || val > INT_MAX) return -EINVAL Kind regards, Stefan -- 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
