From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
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@xxxxxxxxxx>
---
Documentation/ABI/testing/sysfs-bus-iio | 19 +++++++++++++++++++
drivers/iio/industrialio-core.c | 1 +
include/linux/iio/types.h | 1 +
3 files changed, 21 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index d3a0c0ef8948..1dfd6c3f2bd0 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -204,6 +204,25 @@ 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: 5.19
+Contact: linux-iio@xxxxxxxxxxxxxxx
+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
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 8225d0c43010..fbd7d6bd6f98 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -169,6 +169,7 @@ static const char * const iio_chan_info_postfix[] = {
[IIO_CHAN_INFO_OVERSAMPLING_RATIO] = "oversampling_ratio",
[IIO_CHAN_INFO_THERMOCOUPLE_TYPE] = "thermocouple_type",
[IIO_CHAN_INFO_CALIBAMBIENT] = "calibambient",
+ [IIO_CHAN_INFO_ZEROPOINT] = "zeropoint",
};
/**
* iio_device_id() - query the unique ID for the device
diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
index a7aa91f3a8dc..27143b03909d 100644
--- a/include/linux/iio/types.h
+++ b/include/linux/iio/types.h
@@ -63,6 +63,7 @@ enum iio_chan_info_enum {
IIO_CHAN_INFO_OVERSAMPLING_RATIO,
IIO_CHAN_INFO_THERMOCOUPLE_TYPE,
IIO_CHAN_INFO_CALIBAMBIENT,
+ IIO_CHAN_INFO_ZEROPOINT,
};
#endif /* _IIO_TYPES_H_ */
--
2.36.1
