From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Stefan =?ISO-8859-1?Q?Br=FCns?= To: Maciej Purski CC: Jonathan Cameron , , , , "Peter Meerwald-Stadler" , Lars-Peter Clausen , Hartmut Knaack , Jean Delvare , "Guenter Roeck" , Marek Szyprowski , Bartlomiej Zolnierkiewicz Subject: Re: [PATCH v4] iio: adc: ina2xx: Make calibration register value fixed Date: Mon, 18 Dec 2017 10:02:44 +0100 Message-ID: <5526600.j0ivttN8ph@bacchus.fritz.box> In-Reply-To: <1513586638-6036-1-git-send-email-m.purski@samsung.com> References: <1513586638-6036-1-git-send-email-m.purski@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" List-ID: On Monday, December 18, 2017 9:43:58 AM CET Maciej Purski wrote: > Calibration register is used for calculating current register in > hardware according to datasheet: > current =3D shunt_volt * calib_register / 2048 (ina 226) > current =3D shunt_volt * calib_register / 4096 (ina 219) >=20 > 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. >=20 > Power_lsb value should also follow shunt_resistor changes as stated in > datasheet: > power_lsb =3D 25 * current_lsb (ina 226) > power_lsb =3D 20 * current_lsb (ina 219) >=20 > This is a part of the patchset: https://lkml.org/lkml/2017/11/22/394 >=20 > Signed-off-by: Maciej Purski Reviewed-by: Stefan Br=FCns > --- > Changes in v4: > - fix comments >=20 > Changes in v3: > - remove variable current_lsb and calculate it on each read of current > and power scale value > - update comments >=20 > 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 | 64 > +++++++++++++++++++++++--------------------- 1 file changed, 33 > insertions(+), 31 deletions(-) >=20 > diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c > index ddf8781..9e8ca12 100644 > --- a/drivers/iio/adc/ina2xx-adc.c > +++ b/drivers/iio/adc/ina2xx-adc.c > @@ -124,11 +124,12 @@ enum ina2xx_ids { ina219, ina226 }; >=20 > 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; > }; >=20 > @@ -149,20 +150,20 @@ struct ina2xx_chip_info { > static const struct ina2xx_config ina2xx_config[] =3D { > [ina219] =3D { > .config_default =3D INA219_CONFIG_DEFAULT, > - .calibration_factor =3D 40960000, > + .calibration_value =3D 4096, > .shunt_voltage_lsb =3D 10000, > .bus_voltage_shift =3D INA219_BUS_VOLTAGE_SHIFT, > .bus_voltage_lsb =3D 4000, > - .power_lsb =3D 20000, > + .power_lsb_factor =3D 20, > .chip_id =3D ina219, > }, > [ina226] =3D { > .config_default =3D INA226_CONFIG_DEFAULT, > - .calibration_factor =3D 5120000, > + .calibration_value =3D 2048, > .shunt_voltage_lsb =3D 2500, > .bus_voltage_shift =3D 0, > .bus_voltage_lsb =3D 1250, > - .power_lsb =3D 25000, > + .power_lsb_factor =3D 25, > .chip_id =3D ina226, > }, > }; > @@ -227,16 +228,26 @@ static int ina2xx_read_raw(struct iio_dev *indio_de= v, > *val2 =3D 1000; > return IIO_VAL_FRACTIONAL; >=20 > - case INA2XX_POWER: > - /* processed (mW) =3D raw*lsb (uW) / 1000 */ > - *val =3D chip->config->power_lsb; > - *val2 =3D 1000; > + case INA2XX_CURRENT: > + /* > + * processed (mA) =3D raw * current_lsb (mA) > + * current_lsb (mA) =3D shunt_voltage_lsb (nV) / > + * shunt_resistor (uOhm) > + */ > + *val =3D chip->config->shunt_voltage_lsb; > + *val2 =3D chip->shunt_resistor_uohm; > return IIO_VAL_FRACTIONAL; >=20 > - case INA2XX_CURRENT: > - /* processed (mA) =3D raw (mA) */ > - *val =3D 1; > - return IIO_VAL_INT; > + case INA2XX_POWER: > + /* > + * processed (mW) =3D raw * power_lsb (mW) > + * power_lsb (mW) =3D power_lsb_factor (mW/mA) * > + * current_lsb (mA) > + */ > + *val =3D chip->config->power_lsb_factor * > + chip->config->shunt_voltage_lsb; > + *val2 =3D chip->shunt_resistor_uohm; > + return IIO_VAL_FRACTIONAL; > } >=20 > case IIO_CHAN_INFO_HARDWAREGAIN: > @@ -541,25 +552,21 @@ static ssize_t ina2xx_allow_async_readout_store(str= uct > device *dev, } >=20 > /* > - * 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 =3D 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); > } >=20 > static int set_shunt_resistor(struct ina2xx_chip_info *chip, unsigned int > val) { > - if (val <=3D 0 || val > chip->config->calibration_factor) > + if (val =3D=3D 0 || val > INT_MAX) > return -EINVAL; >=20 > chip->shunt_resistor_uohm =3D val; > @@ -592,11 +599,6 @@ static ssize_t ina2xx_shunt_resistor_store(struct > device *dev, if (ret) > return ret; >=20 > - /* Update the Calibration register */ > - ret =3D ina2xx_set_calibration(chip); > - if (ret) > - return ret; > - > return len; > } =2D-=20 Stefan Br=FCns / Bergstra=DFe 21 / 52062 Aachen phone: +49 241 53809034 mobile: +49 151 50412019