iio: cdc: ad7746: Add device specific ABI documentation.

The datasheet description of offset calibration is complex, so for that
on just refer the reader to the device datasheet.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220626122938.582107-16-jic23@kernel.org

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-cdc-ad7746 b/Documentation/ABI/testing/sysfs-bus-iio-cdc-ad7746
new file mode 100644 (file)
index 0000000..02ca894
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-cdc-ad7746
@@ -0,0 +1,11 @@
+What:          /sys/.../iio:deviceX/in_capacitableY_calibbias_calibration
+What:          /sys/.../iio:deviceX/in_capacitableY_calibscale_calibration
+KernelVersion: 6.1
+Contact:       linux-iio@vger.kernel.org
+Description:
+               Write 1 to trigger a calibration of the calibbias or
+               calibscale. For calibscale, a full scale capacitance should
+               be connected to the capacitance input and a
+               calibscale_calibration then started.  For calibbias see
+               the device datasheet section on "capacitive system offset
+               calibration".