From 5c64990b99aa91622cf044a9a2f7a78de8f770a2 Mon Sep 17 00:00:00 2001 From: Jonathan Cameron Date: Sun, 26 Jun 2022 13:29:32 +0100 Subject: 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 Reviewed-by: Andy Shevchenko Link: https://lore.kernel.org/r/20220626122938.582107-12-jic23@kernel.org --- Documentation/ABI/testing/sysfs-bus-iio | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'Documentation/ABI') diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio index 979f2e2b44f6..80e8a38d1ee2 100644 --- a/Documentation/ABI/testing/sysfs-bus-iio +++ b/Documentation/ABI/testing/sysfs-bus-iio @@ -207,6 +207,25 @@ Description: is required is a consistent labeling. Units after application of scale and offset are nanofarads. +What: /sys/.../iio:deviceX/in_capacitanceY-capacitanceZ_zeropoint +KernelVersion: 6.1 +Contact: linux-iio@vger.kernel.org +Description: + For differential channels, this an offset that is applied + equally to both inputs. As the reading is of the difference + between the two inputs, this should not be applied to the _raw + reading by userspace (unlike _offset) and unlike calibbias + it does not affect the differential value measured because + the effect of _zeropoint cancels out across the two inputs + that make up the differential pair. It's purpose is to bring + the individual signals, before the differential is measured, + within the measurement range of the device. The naming is + chosen because if the separate inputs that make the + differential pair are drawn on a graph in their + _raw units, this is the value that the zero point on the + measurement axis represents. It is expressed with the + same scaling as _raw. + What: /sys/bus/iio/devices/iio:deviceX/in_temp_raw What: /sys/bus/iio/devices/iio:deviceX/in_tempX_raw What: /sys/bus/iio/devices/iio:deviceX/in_temp_x_raw -- cgit