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SubjectRe: [PATCH v2 2/5] hwmon: ina2xx: make shunt resistance configurable at run-time
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@baylibre.com>
> ---
> 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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