hwmon: (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)

Signed-off-by: Maciej Purski <m.purski@samsung.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
index 62e38fa8cda23c790635664364ba90e6d8292414..e362a932fe8c03f4d5029c401afd57a9d28f64b6 100644 (file)
--- a/drivers/hwmon/ina2xx.c
+++ b/drivers/hwmon/ina2xx.c
@@ -95,18 +95,20 @@ enum ina2xx_ids { ina219, ina226 };
 
 struct ina2xx_config {
        u16 config_default;
-       int calibration_factor;
+       int calibration_value;
        int registers;
        int shunt_div;
        int bus_voltage_shift;
        int bus_voltage_lsb;    /* uV */
-       int power_lsb;          /* uW */
+       int power_lsb_factor;
 };
 
 struct ina2xx_data {
        const struct ina2xx_config *config;
 
        long rshunt;
+       long current_lsb_uA;
+       long power_lsb_uW;
        struct mutex config_lock;
        struct regmap *regmap;
 
@@ -116,21 +118,21 @@ struct ina2xx_data {
 static const struct ina2xx_config ina2xx_config[] = {
        [ina219] = {
                .config_default = INA219_CONFIG_DEFAULT,
-               .calibration_factor = 40960000,
+               .calibration_value = 4096,
                .registers = INA219_REGISTERS,
                .shunt_div = 100,
                .bus_voltage_shift = 3,
                .bus_voltage_lsb = 4000,
-               .power_lsb = 20000,
+               .power_lsb_factor = 20,
        },
        [ina226] = {
                .config_default = INA226_CONFIG_DEFAULT,
-               .calibration_factor = 5120000,
+               .calibration_value = 2048,
                .registers = INA226_REGISTERS,
                .shunt_div = 400,
                .bus_voltage_shift = 0,
                .bus_voltage_lsb = 1250,
-               .power_lsb = 25000,
+               .power_lsb_factor = 25,
        },
 };
 
@@ -169,12 +171,16 @@ static u16 ina226_interval_to_reg(int interval)
        return INA226_SHIFT_AVG(avg_bits);
 }
 
+/*
+ * 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
+ * ina226 and 4096 for ina219. They are hardcoded as calibration_value.
+ */
 static int ina2xx_calibrate(struct ina2xx_data *data)
 {
-       u16 val = DIV_ROUND_CLOSEST(data->config->calibration_factor,
-                                   data->rshunt);
-
-       return regmap_write(data->regmap, INA2XX_CALIBRATION, val);
+       return regmap_write(data->regmap, INA2XX_CALIBRATION,
+                           data->config->calibration_value);
 }
 
 /*
@@ -187,10 +193,6 @@ static int ina2xx_init(struct ina2xx_data *data)
        if (ret < 0)
                return ret;
 
-       /*
-        * Set current LSB to 1mA, shunt is in uOhms
-        * (equation 13 in datasheet).
-        */
        return ina2xx_calibrate(data);
 }
 
@@ -268,15 +270,15 @@ static int ina2xx_get_value(struct ina2xx_data *data, u8 reg,
                val = DIV_ROUND_CLOSEST(val, 1000);
                break;
        case INA2XX_POWER:
-               val = regval * data->config->power_lsb;
+               val = regval * data->power_lsb_uW;
                break;
        case INA2XX_CURRENT:
-               /* signed register, LSB=1mA (selected), in mA */
-               val = (s16)regval;
+               /* signed register, result in mA */
+               val = regval * data->current_lsb_uA;
+               val = DIV_ROUND_CLOSEST(val, 1000);
                break;
        case INA2XX_CALIBRATION:
-               val = DIV_ROUND_CLOSEST(data->config->calibration_factor,
-                                       regval);
+               val = regval;
                break;
        default:
                /* programmer goofed */
@@ -304,9 +306,32 @@ static ssize_t ina2xx_show_value(struct device *dev,
                        ina2xx_get_value(data, attr->index, regval));
 }
 
-static ssize_t ina2xx_set_shunt(struct device *dev,
-                               struct device_attribute *da,
-                               const char *buf, size_t count)
+/*
+ * 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 ina2xx_set_shunt(struct ina2xx_data *data, long val)
+{
+       unsigned int dividend = DIV_ROUND_CLOSEST(1000000000,
+                                                 data->config->shunt_div);
+       if (val <= 0 || val > dividend)
+               return -EINVAL;
+
+       mutex_lock(&data->config_lock);
+       data->rshunt = val;
+       data->current_lsb_uA = DIV_ROUND_CLOSEST(dividend, val);
+       data->power_lsb_uW = data->config->power_lsb_factor *
+                            data->current_lsb_uA;
+       mutex_unlock(&data->config_lock);
+
+       return 0;
+}
+
+static ssize_t ina2xx_store_shunt(struct device *dev,
+                                 struct device_attribute *da,
+                                 const char *buf, size_t count)
 {
        unsigned long val;
        int status;
@@ -316,18 +341,9 @@ static ssize_t ina2xx_set_shunt(struct device *dev,
        if (status < 0)
                return status;
 
-       if (val == 0 ||
-           /* Values greater than the calibration factor make no sense. */
-           val > data->config->calibration_factor)
-               return -EINVAL;
-
-       mutex_lock(&data->config_lock);
-       data->rshunt = val;
-       status = ina2xx_calibrate(data);
-       mutex_unlock(&data->config_lock);
+       status = ina2xx_set_shunt(data, val);
        if (status < 0)
                return status;
-
        return count;
 }
 
@@ -387,7 +403,7 @@ static SENSOR_DEVICE_ATTR(power1_input, S_IRUGO, ina2xx_show_value, NULL,
 
 /* shunt resistance */
 static SENSOR_DEVICE_ATTR(shunt_resistor, S_IRUGO | S_IWUSR,
-                         ina2xx_show_value, ina2xx_set_shunt,
+                         ina2xx_show_value, ina2xx_store_shunt,
                          INA2XX_CALIBRATION);
 
 /* update interval (ina226 only) */
@@ -448,10 +464,7 @@ static int ina2xx_probe(struct i2c_client *client,
                        val = INA2XX_RSHUNT_DEFAULT;
        }
 
-       if (val <= 0 || val > data->config->calibration_factor)
-               return -ENODEV;
-
-       data->rshunt = val;
+       ina2xx_set_shunt(data, val);
 
        ina2xx_regmap_config.max_register = data->config->registers;