Jonathan Cameron 5c64990b99 iio: core: Introduce _zeropoint for differential channels
Address an ABI gap for device where the offset of both lines in a
differential pair may be controlled so as to allow a wider range of
inputs, but without having any direct effect of the differential
measurement.

_offset cannot be used as to remain in line with existing usage,
userspace would be expected to apply it as (_raw + _offset) * _scale
whereas _zeropoint is not. i.e. If we were computing the differential
in software it would be.
((postive_raw + _zeropoint) - (negative_raw + zeropoint) + _offset) * _scale
= ((postive_raw - negative_raw) + _offset) * _scale
= (differential_raw + _offset) * _scale

Similarly calibbias is expected to tweak the measurement seen, not
the adjust the two lines of the differential pair.

Needed for in_capacitanceX-capacitanceY_zeropoint for the
AD7746 CDC driver.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220626122938.582107-12-jic23@kernel.org
2022-08-15 22:30:01 +01:00
2022-08-12 09:07:33 -07:00
2022-08-14 15:50:18 -07:00

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