Re: [PATCH v2 2/5] hwmon: ina2xx: make shunt resistance configurable at run-time

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On 11/27/2014 01:59 AM, Bartosz Golaszewski wrote:
The shunt resistance can only be set via platform_data or device tree. This
isn't suitable for devices in which the shunt resistance can change/isn't
known at boot-time.

Add a sysfs attribute that allows to read and set the shunt resistance.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
---
  drivers/hwmon/ina2xx.c | 62 +++++++++++++++++++++++++++++++++++++++++++++-----
  1 file changed, 56 insertions(+), 6 deletions(-)

diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
index 0a6b60f..341da67 100644
--- a/drivers/hwmon/ina2xx.c
+++ b/drivers/hwmon/ina2xx.c
@@ -51,6 +51,8 @@
  #define INA226_ALERT_LIMIT		0x07
  #define INA226_DIE_ID			0xFF

+/* shunt resistor sysfs attribute index */
+#define INA2XX_RSHUNT			0x8

  /* register count */
  #define INA219_REGISTERS		6
@@ -65,6 +67,9 @@
  /* worst case is 68.10 ms (~14.6Hz, ina219) */
  #define INA2XX_CONVERSION_RATE		15

+/* default shunt resistance */
+#define INA2XX_RSHUNT_DEFAULT		10000
+
  enum ina2xx_ids { ina219, ina226 };

  struct ina2xx_config {
@@ -87,6 +92,8 @@ struct ina2xx_data {

  	int kind;
  	u16 regs[INA2XX_MAX_REGISTERS];
+
+	long rshunt;
  };

  static const struct ina2xx_config ina2xx_config[] = {
@@ -110,6 +117,11 @@ static const struct ina2xx_config ina2xx_config[] = {
  	},
  };

+static u16 ina2xx_calibration_val(const struct ina2xx_data *data)
+{
+	return data->config->calibration_factor / data->rshunt;
+}
+
  static struct ina2xx_data *ina2xx_update_device(struct device *dev)
  {
  	struct ina2xx_data *data = dev_get_drvdata(dev);
@@ -164,6 +176,9 @@ static int ina2xx_get_value(struct ina2xx_data *data, u8 reg)
  		/* signed register, LSB=1mA (selected), in mA */
  		val = (s16)data->regs[reg];
  		break;
+	case INA2XX_RSHUNT:
+		val = data->rshunt;
+		break;

That doesn't make sense. You neither read the current shunt resistor value
with update_device, nor use the register value to calculate the programmed
shunt resistor value. Just define a separate show function which reports
rshunt as configured.

A better alternative would be to actually _read_ and report rshunt as
programmed into the chip. Otherwise you'll get the "old" value of rshunt
even if the chip was, as your use case suggests, pulled and re-inserted.

  	default:
  		/* programmer goofed */
  		WARN_ON_ONCE(1);
@@ -187,6 +202,35 @@ static ssize_t ina2xx_show_value(struct device *dev,
  			ina2xx_get_value(data, attr->index));
  }

+static ssize_t ina2xx_set_shunt(struct device *dev,
+				struct device_attribute *da,
+				const char *buf, size_t count)
+{
+	struct ina2xx_data *data = ina2xx_update_device(dev);
+	long val;

This should be unsigned long since you now use kstrtoul.

+	int status;
+
+	if (IS_ERR(data))
+		return PTR_ERR(data);
+
+	status = kstrtoul(buf, 10, &val);
+	if (status < 0)
+		return status;

This will accept a value of 0xffffffff which is then converted into -1
since data->rshunt is defined as long.

+
+	if (val == 0)
+		return -EINVAL;
+
+	mutex_lock(&data->update_lock);
+	data->rshunt = val;
+	status = i2c_smbus_write_word_swapped(data->client, INA2XX_CALIBRATION,
+					      ina2xx_calibration_val(data));
+	mutex_unlock(&data->update_lock);
+	if (status < 0)
+		return status;
+
+	return count;
+}
+
  /* shunt voltage */
  static SENSOR_DEVICE_ATTR(in0_input, S_IRUGO, ina2xx_show_value, NULL,
  			  INA2XX_SHUNT_VOLTAGE);
@@ -203,12 +247,17 @@ static SENSOR_DEVICE_ATTR(curr1_input, S_IRUGO, ina2xx_show_value, NULL,
  static SENSOR_DEVICE_ATTR(power1_input, S_IRUGO, ina2xx_show_value, NULL,
  			  INA2XX_POWER);

+/* shunt resistance */
+static SENSOR_DEVICE_ATTR(shunt_resistor, S_IRUGO | S_IWUSR | S_IWGRP,

This will have to be S_IRUGO | S_IWUSR. We don't permit group writes.

+			  ina2xx_show_value, ina2xx_set_shunt, INA2XX_RSHUNT);
+
  /* pointers to created device attributes */
  static struct attribute *ina2xx_attrs[] = {
  	&sensor_dev_attr_in0_input.dev_attr.attr,
  	&sensor_dev_attr_in1_input.dev_attr.attr,
  	&sensor_dev_attr_curr1_input.dev_attr.attr,
  	&sensor_dev_attr_power1_input.dev_attr.attr,
+	&sensor_dev_attr_shunt_resistor.dev_attr.attr,
  	NULL,
  };
  ATTRIBUTE_GROUPS(ina2xx);
@@ -221,7 +270,6 @@ static int ina2xx_probe(struct i2c_client *client,
  	struct device *dev = &client->dev;
  	struct ina2xx_data *data;
  	struct device *hwmon_dev;
-	long shunt = 10000; /* default shunt value 10mOhms */
  	u32 val;
  	int ret;

@@ -234,13 +282,15 @@ static int ina2xx_probe(struct i2c_client *client,

  	if (dev_get_platdata(dev)) {
  		pdata = dev_get_platdata(dev);
-		shunt = pdata->shunt_uohms;
+		data->rshunt = pdata->shunt_uohms;
  	} else if (!of_property_read_u32(dev->of_node,
  					 "shunt-resistor", &val)) {
-		shunt = val;
+		data->rshunt = val;
+	} else {
+		data->rshunt = INA2XX_RSHUNT_DEFAULT;
  	}

-	if (shunt <= 0)
+	if (data->rshunt <= 0)
  		return -ENODEV;

  	/* set the device type */
@@ -260,7 +310,7 @@ static int ina2xx_probe(struct i2c_client *client,
  	 * (equation 13 in datasheet).
  	 */
  	ret = i2c_smbus_write_word_swapped(client, INA2XX_CALIBRATION,
-				data->config->calibration_factor / shunt);
+					   ina2xx_calibration_val(data));
  	if (ret < 0) {
  		dev_err(dev,
  			"error writing to the calibration register: %d", ret);
@@ -276,7 +326,7 @@ static int ina2xx_probe(struct i2c_client *client,
  		return PTR_ERR(hwmon_dev);

  	dev_info(dev, "power monitor %s (Rshunt = %li uOhm)\n",
-		 id->name, shunt);
+		 id->name, data->rshunt);

  	return 0;
  }



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