[PATCH v1 2/3] iio: ABI: adc: ad4130: document filter_mode{,_available}

[Cosmin Tanislav]

AD4130-8 is an ultra-low power, high precision,
measurement solution for low bandwidth battery
operated applications.

The fully integrated AFE (Analog Front-End)
includes a multiplexer for up to 16 single-ended
or 8 differential inputs, PGA (Programmable Gain
Amplifier), 24-bit Sigma-Delta ADC, on-chip
reference and oscillator, selectable filter
options, smart sequencer, sensor biasing and
excitation options, diagnostics, and a FIFO
buffer.

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@xxxxxxxxxx>
---
 .../ABI/testing/sysfs-bus-iio-adc-ad4130      | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130 b/Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130
new file mode 100644
index 000000000000..942150991e75
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130
@@ -0,0 +1,36 @@
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltage-voltage_filter_mode_available
+KernelVersion:
+Contact:	linux-iio@xxxxxxxxxxxxxxx
+Description:
+		Reading returns a list with the possible filter modes.
+		"sinc4"       - Sinc 4. Excellent noise performance. Long 1st
+				conversion time. No natural 50/60Hz rejection.
+		"sinc4+sinc1" - Sinc4 + averaging by 8. Low 1st conversion time.
+		"sinc3"	      - Sinc3. Moderate 1st conversion time. Good noise
+				performance.
+		"sinc3+rej60" - Sinc3 + 60Hz rejection. At a sampling frequency
+				of 50Hz, achieves simultaneous 50Hz and 60Hz
+				rejection.
+		"sinc3+sinc1" - Sinc3 + averaging by 8. Low 1st conversion time.
+				Best used with a sampling frequency of at least
+				216.19Hz.
+		"sinc3+pf1"   - Sinc3 + Post Filter 1.
+				53dB rejection @ 50Hz, 58dB rejection @ 60Hz.
+		"sinc3+pf2"   - Sinc3 + Post Filter 2.
+				70dB rejection @ 50Hz, 70dB rejection @ 60Hz.
+		"sinc3+pf3"   - Sinc3 + Post Filter 3.
+				99dB rejection @ 50Hz, 103dB rejection @ 60Hz.
+		"sinc3+pf4"   - Sinc3 + Post Filter 4.
+				103dB rejection @ 50Hz, 109dB rejection @ 60Hz.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY-voltageZ_filter_mode
+KernelVersion:
+Contact:	linux-iio@xxxxxxxxxxxxxxx
+Description:
+		Set the filter mode of the differential channel. When the filter
+		mode changes, the in_voltageY-voltageZ_sampling_frequency and
+		in_voltageY-voltageZ_sampling_frequency_available attributes
+		might also change to accomodate the new filter mode.
+		If the current sampling frequency is out of range for the new
+		filter mode, the sampling frequency will be changed to the
+		closest valid one.
-- 
2.35.1