Documentation: ABI: testing: ad7192: update sysfs docs

Updated mainline documentation on ad7192 userspace sysfs.

Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-adc-ad7192

@@ -2,17 +2,22 @@ What:		/sys/bus/iio/devices/iio:deviceX/ac_excitation_en
 KernelVersion:
 Contact:	linux-iio@vger.kernel.org
 Description:
-		Reading gives the state of AC excitation.
-		Writing '1' enables AC excitation.
+		This attribute, if available, is used to enable the AC
+		excitation mode found on some converters. In ac excitation mode,
+		the polarity of the excitation voltage is reversed on
+		alternate cycles, to eliminate DC errors.
 
 What:		/sys/bus/iio/devices/iio:deviceX/bridge_switch_en
 KernelVersion:
 Contact:	linux-iio@vger.kernel.org
 Description:
-		This bridge switch is used to disconnect it when there is a
-		need to minimize the system current consumption.
-		Reading gives the state of the bridge switch.
-		Writing '1' enables the bridge switch.
+		This attribute, if available, is used to close or open the
+		bridge power down switch found on some converters.
+		In bridge applications, such as strain gauges and load cells,
+		the bridge itself consumes the majority of the current in the
+		system. To minimize the current consumption of the system,
+		the bridge can be disconnected (when it is not being used
+		using the bridge_switch_en attribute.
 
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltagex_sys_calibration
 KernelVersion:
@@ -21,6 +26,13 @@ Description:
 		Initiates the system calibration procedure. This is done on a
 		single channel at a time. Write '1' to start the calibration.
 
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltage2-voltage2_shorted_raw
+KernelVersion:
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Measure voltage from AIN2 pin connected to AIN(+)
+		and AIN(-) shorted.
+
 What:		/sys/bus/iio/devices/iio:deviceX/in_voltagex_sys_calibration_mode_available
 KernelVersion:
 Contact:	linux-iio@vger.kernel.org