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iio: adc: ina2xx: Make calibration register value fixed

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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@samsung.com>
Reviewed-by:  Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Maciej Purski 2017-12-18 09:43:58 +01:00 committed by Greg Kroah-Hartman
parent bbdcbd12a5
commit a28caa7b8f
1 changed files with 33 additions and 31 deletions
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64
drivers/iio/adc/ina2xx-adc.c
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@ -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;
}