counter: 104-quad-8: Documentation: Add Generic Counter sysfs documentation

This patch adds standard documentation for the Generic Counter interface
userspace sysfs attributes of the 104-QUAD-8 driver.
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-bus-counter-104-quad-8

+What:		/sys/bus/counter/devices/counterX/signalY/index_polarity
+KernelVersion:	5.2
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Active level of index input Signal Y; irrelevant in
+		non-synchronous load mode.
+
+What:		/sys/bus/counter/devices/counterX/signalY/index_polarity_available
+What:		/sys/bus/counter/devices/counterX/signalY/synchronous_mode_available
+KernelVersion:	5.2
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Discrete set of available values for the respective Signal Y
+		configuration are listed in this file.
+
+What:		/sys/bus/counter/devices/counterX/signalY/synchronous_mode
+KernelVersion:	5.2
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Configure the counter associated with Signal Y for
+		non-synchronous or synchronous load mode. Synchronous load mode
+		cannot be selected in non-quadrature (Pulse-Direction) clock
+		mode.
+
+		non-synchronous:
+			A logic low level is the active level at this index
+			input. The index function (as enabled via preset_enable)
+			is performed directly on the active level of the index
+			input.
+
+		synchronous:
+			Intended for interfacing with encoder Index output in
+			quadrature clock mode. The active level is configured
+			via index_polarity. The index function (as enabled via
+			preset_enable) is performed synchronously with the
+			quadrature clock on the active level of the index input.

MAINTAINERS

@@ -272,6 +272,7 @@ ACCES 104-QUAD-8 DRIVER
 M:	William Breathitt Gray <vilhelm.gray@gmail.com>
 L:	linux-iio@vger.kernel.org
 S:	Maintained
+F:	Documentation/ABI/testing/sysfs-bus-counter-104-quad-8
 F:	Documentation/ABI/testing/sysfs-bus-iio-counter-104-quad-8
 F:	drivers/counter/104-quad-8.c