ABI: debugfs-iio-ad9467: document the debugfs interface

Document the debugfs interface for the IIO ad9467 high speed ADC.
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
Link: https://patch.msgid.link/20240806-dev-ad-debugfs-doc-v1-2-153b882a3f01@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/debugfs-iio-ad9467

+What:		/sys/kernel/debug/iio/iio:deviceX/calibration_table_dump
+KernelVersion:	6.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This dumps the calibration table that was filled during the
+		digital interface tuning process.
+
+What:		/sys/kernel/debug/iio/iio:deviceX/in_voltage_test_mode_available
+KernelVersion:	6.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		List all the available test tones:
+		- off
+		- midscale_short
+		- pos_fullscale
+		- neg_fullscale
+		- checkerboard
+		- prbs23
+		- prbs9
+		- one_zero_toggle
+		- user
+		- bit_toggle
+		- sync
+		- one_bit_high
+		- mixed_bit_frequency
+		- ramp
+
+		Note that depending on the actual device being used, some of the
+		above might not be available (and they won't be listed when
+		reading the file).
+
+What:		/sys/kernel/debug/iio/iio:deviceX/in_voltageY_test_mode
+KernelVersion:	6.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Writing to this file will initiate one of available test tone on
+		channel Y. Reading it, shows which test is running. In cases
+		where an IIO backend is available and supports the test tone,
+		additional information about the data correctness is given.

MAINTAINERS

@@ -1316,6 +1316,7 @@ M:	Nuno Sa <nuno.sa@analog.com>
 L:	linux-iio@vger.kernel.org
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
+F:	Documentation/ABI/testing/debugfs-iio-ad9467
 F:	Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml
 F:	drivers/iio/adc/ad9467.c