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SubjectRe: [PATCH 1/2] iio: adc: ina2xx: Make calibration register value fixed
Date
On Wednesday, November 22, 2017 4:32:14 PM 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)
>
> Signed-off-by: Maciej Purski <m.purski@samsung.com>

Looks fine in general, but will need rebasing on top of Jonathans git tree.
Some comments inline ...

Kind regards,

Stefan

> ---
> drivers/iio/adc/ina2xx-adc.c | 59
> ++++++++++++++++++++++++-------------------- 1 file changed, 32
> insertions(+), 27 deletions(-)
>
> diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> index 84a4387..0f25087 100644
> --- a/drivers/iio/adc/ina2xx-adc.c
> +++ b/drivers/iio/adc/ina2xx-adc.c
> @@ -110,11 +110,11 @@ enum ina2xx_ids { ina219, ina226 };
>
> struct ina2xx_config {
> u16 config_default;
> - int calibration_factor;
> + int calibration_value;
> int shunt_div;
> int bus_voltage_shift;
> int bus_voltage_lsb; /* uV */
> - int power_lsb; /* uW */
> + int power_lsb_factor;
> enum ina2xx_ids chip_id;
> };
>
> @@ -124,6 +124,8 @@ struct ina2xx_chip_info {
> const struct ina2xx_config *config;
> struct mutex state_lock;
> unsigned int shunt_resistor_uohm;
> + unsigned int current_lsb_uA;
> + unsigned int power_lsb_uW;

I think power_lsb_uW is unneeded, see below.

> int avg;
> int int_time_vbus; /* Bus voltage integration time uS */
> int int_time_vshunt; /* Shunt voltage integration time uS */
> @@ -133,20 +135,20 @@ struct ina2xx_chip_info {
> static const struct ina2xx_config ina2xx_config[] = {
> [ina219] = {
> .config_default = INA219_CONFIG_DEFAULT,
> - .calibration_factor = 40960000,
> + .calibration_value = 4096,
> .shunt_div = 100,
> .bus_voltage_shift = 3,
> .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_div = 400,
> .bus_voltage_shift = 0,
> .bus_voltage_lsb = 1250,
> - .power_lsb = 25000,
> + .power_lsb_factor = 25,
> .chip_id = ina226,
> },
> };
> @@ -210,14 +212,15 @@ 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->power_lsb_uW;
> *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;
> }
> }
>
> @@ -434,28 +437,35 @@ 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 (eq. 3) the best values are 2048 for

Nitpick - eq. 3 is only correct for INA226, IIRC, so maybe:
(INA226: Eq. 3, INA219: Eq. ?)

> + * 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);
> + chip->power_lsb_uW = chip->config->power_lsb_factor *
> + chip->current_lsb_uA;

As the calculation is trivial an only used in ina2xx_read_raw, I think you
should remove the extra struct member and do the calculation in
ina2xx_read_raw.


> return 0;
> }
> @@ -485,11 +495,6 @@ 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;
> }


--
Stefan Brüns / Bergstraße 21 / 52062 Aachen
home: +49 241 53809034 mobile: +49 151 50412019[unhandled content-type:application/pgp-signature]
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