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| author | Jonathan Cameron <Jonathan.Cameron@huawei.com> | 2022-06-26 13:29:32 +0100 |
|---|---|---|
| committer | Jonathan Cameron <Jonathan.Cameron@huawei.com> | 2022-08-15 22:30:01 +0100 |
| commit | 5c64990b99aa91622cf044a9a2f7a78de8f770a2 (patch) | |
| tree | 7dd6a06389ed9d6bfc41acb2b65d5abf46b919e9 /Documentation/ABI/testing/sysfs-bus-iio | |
| parent | 431e9147b4667d67399fe5db4f8203d55811951b (diff) | |
| download | linux-5c64990b99aa91622cf044a9a2f7a78de8f770a2.tar.gz linux-5c64990b99aa91622cf044a9a2f7a78de8f770a2.tar.bz2 linux-5c64990b99aa91622cf044a9a2f7a78de8f770a2.zip | |
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
Diffstat (limited to 'Documentation/ABI/testing/sysfs-bus-iio')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-bus-iio | 19 |
1 files changed, 19 insertions, 0 deletions
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 |