Re: [PATCH 3/3] iio: adc: ina2xx: Allow setting Shunt Voltage PGA gain and Bus Voltage range

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 1 Oct 2017 21:48:18 +0200
Stefan Brüns <stefan.bruens@rwth-aachen.de> wrote:

> Reducing shunt and bus voltage range improves the accuracy, so allow
> altering the default settings.
> 
> Both settings are exposed as gain values. While for the shunt voltage
> this is straightforward, the bus range settings of 32V (default) and 16V
> are mapped to gain values of 1 resp. 2, to provide a uniform API to
> userspace.
> 
> As the gain settings are incorporated into the raw values by the sensor
> itself, adjusting of the scale attributes is not necessary.
> 
> Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>

cc'd Maciej Purski who is working to improve the current calibration
elements - I'd like you both to review each others patches if possible
as the ABI is getting complex in here!

I think what you have here won't interfere with Maciej's work, but
would like you two to confirm that.  Note that patch set probably
needs a revision as I've suggested a rather different approach.

Thanks,

Jonathan
 
> 
> ---
> 
>  drivers/iio/adc/ina2xx-adc.c | 111 +++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 108 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c
> index 1930f853e8c5..7e9ce43ad15d 100644
> --- a/drivers/iio/adc/ina2xx-adc.c
> +++ b/drivers/iio/adc/ina2xx-adc.c
> @@ -48,8 +48,10 @@
>  #define INA2XX_MAX_REGISTERS            8
>  
>  /* settings - depend on use case */
> -#define INA219_CONFIG_DEFAULT           0x399F	/* PGA=8 */
> +#define INA219_CONFIG_DEFAULT           0x399F	/* PGA=1/8, BRNG=32V */
>  #define INA219_DEFAULT_IT		532
> +#define INA219_DEFAULT_BRNG             1   /* 32V */
> +#define INA219_DEFAULT_PGA              125 /* 1000/8 */
>  #define INA226_CONFIG_DEFAULT           0x4327
>  #define INA226_DEFAULT_AVG              4
>  #define INA226_DEFAULT_IT		1110
> @@ -62,6 +64,14 @@
>   */
>  #define INA2XX_MODE_MASK	GENMASK(3, 0)
>  
> +/* Gain for VShunt: 1/8 (default), 1/4, 1/2, 1 */
> +#define INA219_PGA_MASK		GENMASK(12, 11)
> +#define INA219_SHIFT_PGA(val)	((val) << 11)
> +
> +/* VBus range: 32V (default), 16V */
> +#define INA219_BRNG_MASK	BIT(13)
> +#define INA219_SHIFT_BRNG(val)	((val) << 13)
> +
>  /* Averaging for VBus/VShunt/Power */
>  #define INA226_AVG_MASK		GENMASK(11, 9)
>  #define INA226_SHIFT_AVG(val)	((val) << 9)
> @@ -131,6 +141,8 @@ struct ina2xx_chip_info {
>  	int avg;
>  	int int_time_vbus; /* Bus voltage integration time uS */
>  	int int_time_vshunt; /* Shunt voltage integration time uS */
> +	int range_vbus; /* Bus voltage maximum in V */
> +	int pga_gain_vshunt; /* Shunt voltage PGA gain */
>  	bool allow_async_readout;
>  };
>  
> @@ -227,6 +239,18 @@ static int ina2xx_read_raw(struct iio_dev *indio_dev,
>  			*val = 1;
>  			return IIO_VAL_INT;
>  		}
> +
> +	case IIO_CHAN_INFO_HARDWAREGAIN:
> +		switch (chan->address) {
> +		case INA2XX_SHUNT_VOLTAGE:
> +			*val = chip->pga_gain_vshunt;
> +			*val2 = 1000;
> +			return IIO_VAL_FRACTIONAL;
> +
> +		case INA2XX_BUS_VOLTAGE:
> +			*val = chip->range_vbus == 32 ? 1 : 2;
> +			return IIO_VAL_INT;
> +		}
>  	}
>  
>  	return -EINVAL;
> @@ -361,6 +385,74 @@ static int ina219_set_int_time_vshunt(struct ina2xx_chip_info *chip,
>  	return 0;
>  }
>  
> +static const int ina219_vbus_range_tab[] = { 1, 2 };
> +static int ina219_set_vbus_range_denom(struct ina2xx_chip_info *chip,
> +				       unsigned int range,
> +				       unsigned int *config)
> +{
> +	if (range == 1)
> +		chip->range_vbus = 32;
> +	else if (range == 2)
> +		chip->range_vbus = 16;
> +	else
> +		return -EINVAL;
> +
> +	*config &= ~INA219_BRNG_MASK;
> +	*config |= INA219_SHIFT_BRNG(range == 1 ? 1 : 0) & INA219_BRNG_MASK;
> +
> +	return 0;
> +}
> +
> +static const int ina219_vshunt_gain_tab[] = { 125, 250, 500, 1000 };
> +static const int ina219_vshunt_gain_frac[] = {
> +	125, 1000, 250, 1000, 500, 1000, 1000, 1000 };
> +
> +static int ina219_set_vshunt_pga_gain(struct ina2xx_chip_info *chip,
> +				      unsigned int gain,
> +				      unsigned int *config)
> +{
> +	int bits;
> +
> +	if (gain < 125 || gain > 1000)
> +		return -EINVAL;
> +
> +	bits = find_closest(gain, ina219_vshunt_gain_tab,
> +			    ARRAY_SIZE(ina219_vshunt_gain_tab));
> +
> +	chip->pga_gain_vshunt = ina219_vshunt_gain_tab[bits];
> +	bits = 3 - bits;
> +
> +	*config &= ~INA219_PGA_MASK;
> +	*config |= INA219_SHIFT_PGA(bits) & INA219_PGA_MASK;
> +
> +	return 0;
> +}
> +
> +static int ina2xx_read_avail(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     const int **vals, int *type, int *length,
> +			     long mask)
> +{
> +	switch (mask) {
> +	case IIO_CHAN_INFO_HARDWAREGAIN:
> +		switch (chan->address) {
> +		case INA2XX_SHUNT_VOLTAGE:
> +			*type = IIO_VAL_FRACTIONAL;
> +			*length = sizeof(ina219_vshunt_gain_frac) / sizeof(int);
> +			*vals = ina219_vshunt_gain_frac;
> +			return IIO_AVAIL_LIST;
> +
> +		case INA2XX_BUS_VOLTAGE:
> +			*type = IIO_VAL_INT;
> +			*length = sizeof(ina219_vbus_range_tab) / sizeof(int);
> +			*vals = ina219_vbus_range_tab;
> +			return IIO_AVAIL_LIST;
> +		}
> +	}
> +
> +	return -EINVAL;
> +}
> +
>  static int ina2xx_write_raw(struct iio_dev *indio_dev,
>  			    struct iio_chan_spec const *chan,
>  			    int val, int val2, long mask)
> @@ -403,6 +495,14 @@ static int ina2xx_write_raw(struct iio_dev *indio_dev,
>  		}
>  		break;
>  
> +	case IIO_CHAN_INFO_HARDWAREGAIN:
> +		if (chan->address == INA2XX_SHUNT_VOLTAGE)
> +			ret = ina219_set_vshunt_pga_gain(chip, val * 1000000 +
> +							 val2, &tmp);
> +		else
> +			ret = ina219_set_vbus_range_denom(chip, val, &tmp);
> +		break;
> +
>  	default:
>  		ret = -EINVAL;
>  	}
> @@ -547,7 +647,10 @@ static ssize_t ina2xx_shunt_resistor_store(struct device *dev,
>  	.channel = (_index), \
>  	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
>  			      BIT(IIO_CHAN_INFO_SCALE) | \
> -			      BIT(IIO_CHAN_INFO_INT_TIME), \
> +			      BIT(IIO_CHAN_INFO_INT_TIME) | \
> +			      BIT(IIO_CHAN_INFO_HARDWAREGAIN), \
> +	.info_mask_separate_available = \
> +			      BIT(IIO_CHAN_INFO_HARDWAREGAIN), \
>  	.info_mask_shared_by_dir = BIT(IIO_CHAN_INFO_SAMP_FREQ), \
>  	.scan_index = (_index), \
>  	.scan_type = { \
> @@ -758,7 +861,6 @@ static IIO_CONST_ATTR_NAMED(ina226_integration_time_available,
>  			    integration_time_available,
>  			    "0.000140 0.000204 0.000332 0.000588 0.001100 0.002116 0.004156 0.008244");
>  
> -
>  static IIO_DEVICE_ATTR(in_allow_async_readout, S_IRUGO | S_IWUSR,
>  		       ina2xx_allow_async_readout_show,
>  		       ina2xx_allow_async_readout_store, 0);
> @@ -793,6 +895,7 @@ static const struct iio_info ina219_info = {
>  	.driver_module = THIS_MODULE,
>  	.attrs = &ina219_attribute_group,
>  	.read_raw = ina2xx_read_raw,
> +	.read_avail = ina2xx_read_avail,
>  	.write_raw = ina2xx_write_raw,
>  	.debugfs_reg_access = ina2xx_debug_reg,
>  };
> @@ -874,6 +977,8 @@ static int ina2xx_probe(struct i2c_client *client,
>  		chip->avg = 1;
>  		ina219_set_int_time_vbus(chip, INA219_DEFAULT_IT, &val);
>  		ina219_set_int_time_vshunt(chip, INA219_DEFAULT_IT, &val);
> +		ina219_set_vbus_range_denom(chip, INA219_DEFAULT_BRNG, &val);
> +		ina219_set_vshunt_pga_gain(chip, INA219_DEFAULT_PGA, &val);
>  	}
>  
>  	ret = ina2xx_init(chip, val);