Re: [v8, 5/5] hwmon: ina2xx: allow to change the averaging rate at run-time

[Guenter Roeck]

On Mon, Jan 05, 2015 at 03:20:56PM +0100, Bartosz Golaszewski wrote:
> The averaging rate of ina226 is hardcoded to 16 in the driver. Make it
> modifiable at run-time via a new sysfs attribute.
> 
> While we're at it - add an additional variable to ina2xx_data, which holds
> the current configuration settings - this way we'll be able to restore the
> configuration in case of an unexpected chip reset.
> 
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> ---
>  Documentation/hwmon/ina2xx |   3 ++
>  drivers/hwmon/ina2xx.c     | 129 +++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 128 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/hwmon/ina2xx b/Documentation/hwmon/ina2xx
> index 320dd69..a11256d 100644
> --- a/Documentation/hwmon/ina2xx
> +++ b/Documentation/hwmon/ina2xx
> @@ -48,3 +48,6 @@ The shunt value in micro-ohms can be set via platform data or device tree at
>  compile-time or via the shunt_resistor attribute in sysfs at run-time. Please
>  refer to the Documentation/devicetree/bindings/i2c/ina2xx.txt for bindings
>  if the device tree is used.
> +
> +The averaging rate of INA226 and INA230 can be changed via the avg_rate sysfs
> +attribute. The available rates are: 1, 4, 16, 64, 128, 256, 512 and 1024.

You do accept other values, so you might want to add that other values will be
rounded to the above.

> diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
> index 49537ea..6f6aebd 100644
> --- a/drivers/hwmon/ina2xx.c
> +++ b/drivers/hwmon/ina2xx.c
> @@ -68,6 +68,15 @@
>  
>  #define INA2XX_RSHUNT_DEFAULT		10000
>  
> +/* bit masks for the averaging setting in the configuration register */
> +#define INA226_AVG_RD_MASK		0x0E00
> +#define INA226_AVG_WR_MASK		0xF1FF

You could define INA226_AVG_MASK as 0x0e00 and use ~INA226_AVG_MASK to negate
it. This is more common than the above and less error prone.

> +
> +#define INA226_READ_AVG(reg) ((reg & INA226_AVG_RD_MASK) >> 9)

	(reg)

Also, it might make sense to define INA226_AVG_SHIFT since you use it twice.

> +
> +/* common attrs, ina226 attrs and NULL */
> +#define INA2XX_MAX_ATTRIBUTE_GROUPS	3
> +
>  enum ina2xx_ids { ina219, ina226 };
>  
>  struct ina2xx_config {
> @@ -85,12 +94,14 @@ struct ina2xx_data {
>  	const struct ina2xx_config *config;
>  
>  	long rshunt;
> +	u16 curr_config;
>  
>  	struct mutex update_lock;
>  	bool valid;
>  	unsigned long last_updated;
>  
>  	int kind;
> +	const struct attribute_group *groups[INA2XX_MAX_ATTRIBUTE_GROUPS];
>  	u16 regs[INA2XX_MAX_REGISTERS];
>  };
>  
> @@ -115,6 +126,39 @@ static const struct ina2xx_config ina2xx_config[] = {
>  	},
>  };
>  
> +/*
> + * Available averaging rates for ina226. The indices correspond with
> + * the bit values expected by the chip (according to the ina226 datasheet,
> + * table 3 AVG bit settings, found at
> + * http://www.ti.com/lit/ds/symlink/ina226.pdf.
> + */
> +static const int ina226_avg_tab[] = { 1, 4, 16, 64, 128, 256, 512, 1024 };
> +
> +static int ina226_avg_bits(int avg)
> +{
> +	int i;
> +
> +	/* Get the closest average from the tab. */
> +	for (i = 0; i < ARRAY_SIZE(ina226_avg_tab) - 1; i++) {
> +		if (avg <= (ina226_avg_tab[i] + ina226_avg_tab[i + 1]) / 2)
> +			return i;
> +	}
> +
> +	return i; /* Return 0b0111 for other values. */
> +}
> +
> +static int ina226_avg_val(int bits)
> +{
> +	/*
> +	 * Value read from the config register should be correct, but do check
> +	 * the boundary just in case.
> +	 */
> +	if (bits >= ARRAY_SIZE(ina226_avg_tab))
> +		return -ENODEV;
> +
Logically this can not happen, since the calling code uses INA226_READ_AVG()
which can only return 0..7. So this check is really unnecessary. It might
possibly make sense to pass in the configuration register value and apply  
INA226_READ_AVG in this function to make this more obvious. See more below,
though; the function itself is unnecessary.

> +	return ina226_avg_tab[bits];
> +}
> +
>  static int ina2xx_calibrate(struct ina2xx_data *data)
>  {
>  	return i2c_smbus_write_word_swapped(data->client, INA2XX_CALIBRATION,
> @@ -131,7 +175,7 @@ static int ina2xx_init(struct ina2xx_data *data)
>  
>  	/* device configuration */
>  	ret = i2c_smbus_write_word_swapped(client, INA2XX_CONFIG,
> -					   data->config->config_default);
> +					   data->curr_config);
>  	if (ret < 0)
>  		return ret;
>  
> @@ -292,6 +336,62 @@ static ssize_t ina2xx_set_shunt(struct device *dev,
>  	return count;
>  }
>  
> +static ssize_t ina226_show_avg(struct device *dev,
> +			       struct device_attribute *da, char *buf)
> +{
> +	struct ina2xx_data *data = ina2xx_update_device(dev);
> +	int avg, i;
> +
> +	if (IS_ERR(data))
> +		return PTR_ERR(data);
> +
> +	avg = ina226_avg_val(INA226_READ_AVG(data->regs[INA2XX_CONFIG]));
> +	if (avg < 0)
> +		return avg;
> +
> +	for (i = 0; i < ARRAY_SIZE(ina226_avg_tab); i++) {
> +		if (avg == ina226_avg_tab[i])
> +			break;

ina226_avg_val() calculates the average value from ina226_avg_tab
and then you loop through ina226_avg_tab to find the index into ina226_avg_tab
again, only to use the thus calculated index for accessing ina226_avg_tab[]
once more. Think about it. A simple
	avg = ina226_avg_tab[INA226_READ_AVG(data->regs[INA2XX_CONFIG])];
	return snprintf(buf, PAGE_SIZE, "%d\n", avg);
or even
	return snprintf(buf, PAGE_SIZE, "%d\n",
			ina226_avg_tab[INA226_READ_AVG(data->regs[INA2XX_CONFIG])]);

would accomplish exactly the same.

> +	}
> +
> +	return snprintf(buf, PAGE_SIZE, "%d\n", ina226_avg_tab[i]);
> +}
> +
> +static ssize_t ina226_set_avg(struct device *dev,
> +			      struct device_attribute *da,
> +			      const char *buf, size_t count)
> +{
> +	struct ina2xx_data *data = dev_get_drvdata(dev);
> +	unsigned long val;
> +	int status, avg;
> +
> +	if (IS_ERR(data))
> +		return PTR_ERR(data);
> +
> +	status = kstrtoul(buf, 10, &val);
> +	if (status < 0)
> +		return status;
> +
> +	if (val > INT_MAX || val == 0)
> +		return -EINVAL;
> +
> +	avg = ina226_avg_bits(val);
> +
> +	mutex_lock(&data->update_lock);
> +	data->curr_config = (data->regs[INA2XX_CONFIG] &
> +			     INA226_AVG_WR_MASK) | (avg << 9);
> +	status = i2c_smbus_write_word_swapped(data->client,
> +					      INA2XX_CONFIG,
> +					      data->curr_config);
> +	/* Make sure the next access re-reads all registers. */
> +	data->valid = 0;
> +	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);
> @@ -313,6 +413,10 @@ static SENSOR_DEVICE_ATTR(shunt_resistor, S_IRUGO | S_IWUSR,
>  			  ina2xx_show_value, ina2xx_set_shunt,
>  			  INA2XX_CALIBRATION);
>  
> +/* averaging rate */
> +static SENSOR_DEVICE_ATTR(avg_rate, S_IRUGO | S_IWUSR,

I kind of dislike that attribute name. I don't have a better idea though, so
I'll let it pass unless you have a better idea.

> +			  ina226_show_avg, ina226_set_avg, 0);
> +
>  /* pointers to created device attributes */
>  static struct attribute *ina2xx_attrs[] = {
>  	&sensor_dev_attr_in0_input.dev_attr.attr,
> @@ -322,7 +426,19 @@ static struct attribute *ina2xx_attrs[] = {
>  	&sensor_dev_attr_shunt_resistor.dev_attr.attr,
>  	NULL,
>  };
> -ATTRIBUTE_GROUPS(ina2xx);
> +
> +static const struct attribute_group ina2xx_group = {
> +	.attrs = ina2xx_attrs,
> +};
> +
> +static struct attribute *ina226_attrs[] = {
> +	&sensor_dev_attr_avg_rate.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group ina226_group = {
> +	.attrs = ina226_attrs,
> +};
>  
>  static int ina2xx_probe(struct i2c_client *client,
>  			const struct i2c_device_id *id)
> @@ -333,7 +449,7 @@ static int ina2xx_probe(struct i2c_client *client,
>  	struct ina2xx_data *data;
>  	struct device *hwmon_dev;
>  	u32 val;
> -	int ret;
> +	int ret, group = 0;
>  
>  	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WORD_DATA))
>  		return -ENODEV;
> @@ -355,6 +471,7 @@ static int ina2xx_probe(struct i2c_client *client,
>  	/* set the device type */
>  	data->kind = id->driver_data;
>  	data->config = &ina2xx_config[data->kind];
> +	data->curr_config = data->config->config_default;
>  	data->client = client;
>  
>  	if (data->rshunt <= 0 ||
> @@ -369,8 +486,12 @@ static int ina2xx_probe(struct i2c_client *client,
>  
>  	mutex_init(&data->update_lock);
>  
> +	data->groups[group++] = &ina2xx_group;
> +	if (data->kind == ina226)
> +		data->groups[group++] = &ina226_group;
> +
>  	hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
> -							   data, ina2xx_groups);
> +							   data, data->groups);
>  	if (IS_ERR(hwmon_dev))
>  		return PTR_ERR(hwmon_dev);
>  
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