Re: [PATCH v6 05/17] iio: adc: Add AD7768 and AD7768-4 core support

[Janani Sunil]

On 9/6/26 05:50, Jonathan Cameron wrote:
> > Add core support for the AD7768 and AD7768-4 simultaneous sampling ADCs.
> > Configure supplies, clock and reset, use a custom regmap bus for the SPI
> > protocol, and parse the enabled channels and input buffer settings from
> > devicetree.
> >
> > Connect the converter to an IIO backend for buffered capture with CRC,
> > provide a fixed safe wideband sampling configuration and add runtime
> > power management.
> >
> > Signed-off-by: Janani Sunil <janani.sunil@xxxxxxxxxx>
> ...
>
> > +
> > +static int ad7768_get_enable_vref(struct device *dev, unsigned int index)
> > +{
> > +	const char * const *supply = ad7768_vref_supply_names[index];
> > +	int refp_uV;
> > +	int refn_uV;
> > +
> > +	refp_uV = devm_regulator_get_enable_read_voltage(dev, supply[0]);
> > +	if (refp_uV < 0)
> > +		return dev_err_probe(dev, refp_uV,
> > +				     "Failed to get %s supply voltage\n", supply[0]);
> > +
> > +	refn_uV = devm_regulator_get_enable_read_voltage(dev, supply[1]);
> > +	if (refn_uV == -ENODEV)
> > +		refn_uV = 0;
> > +	else if (refn_uV < 0)
> > +		return dev_err_probe(dev, refn_uV,
> > +				     "Failed to get %s supply voltage\n", supply[1]);
> > +
> > +	if (refp_uV <= refn_uV)
> > +		return dev_err_probe(dev, -EINVAL,
> > +				     "Invalid reference %u voltage\n", index + 1);
> > +
> > +	return refp_uV - refn_uV;
> Do we never care about the offset inherent in where the negative sits?

The absolute REFx- voltage does not introduce an offset into the ADC transfer function. The datasheet defines VREF as REFx+ - REFx- and the LSB size as (2 * VREF)/2^24. Zero code remains at AINx+ - AINx- = 0.

Regards,
Jan