Re: [PATCH 2/2] hwmon: (ina2xx) Make calibration register value fixed
From: Guenter Roeck
Date: Sat Nov 25 2017 - 13:50:35 EST
On 11/22/2017 07:32 AM, 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@xxxxxxxxxxx>
Setting the calibration register to a specific value may optimize precision,
but limits the supported value range, which is the whole point of providing
a calibration register. What am I missing here ?
Guenter
---
drivers/hwmon/ina2xx.c | 87 +++++++++++++++++++++++++++++---------------------
1 file changed, 50 insertions(+), 37 deletions(-)
diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
index 62e38fa..e362a93 100644
--- 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;