iio: adc: ina2xx: Make calibration register value fixed

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>

diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
index 2621a34..94d506f 100644 (file)
--- 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;
 }