iio: core: Introduce IIO_CHAN_INFO_OVERSAMPLING_RATIO

Some magnetometers can perform a number of repetitions in HW
for each measurement to increase accuracy. One example is
Bosch BMC150:
http://ae-bst.resource.bosch.com/media/products/dokumente/bmc150/BST-BMC150-DS000-04.pdf.

Introduce an interface to set the oversampling ratio
for these devices.
Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -1375,3 +1375,15 @@ Description:
 		The emissivity ratio of the surface in the field of view of the
 		contactless temperature sensor.  Emissivity varies from 0 to 1,
 		with 1 being the emissivity of a black body.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_magn_x_oversampling_ratio
+What:		/sys/bus/iio/devices/iio:deviceX/in_magn_y_oversampling_ratio
+What:		/sys/bus/iio/devices/iio:deviceX/in_magn_z_oversampling_ratio
+KernelVersion:	4.2
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Hardware applied number of measurements for acquiring one
+		data point. The HW will do <type>[_name]_oversampling_ratio
+		measurements and return the average value as output data. Each
+		value resulted from <type>[_name]_oversampling_ratio measurements
+		is considered as one sample for <type>[_name]_sampling_frequency.

drivers/iio/industrialio-core.c

@@ -129,6 +129,7 @@ static const char * const iio_chan_info_postfix[] = {
 	[IIO_CHAN_INFO_DEBOUNCE_COUNT] = "debounce_count",
 	[IIO_CHAN_INFO_DEBOUNCE_TIME] = "debounce_time",
 	[IIO_CHAN_INFO_CALIBEMISSIVITY] = "calibemissivity",
+	[IIO_CHAN_INFO_OVERSAMPLING_RATIO] = "oversampling_ratio",
 };
 
 /**

include/linux/iio/iio.h

@@ -44,6 +44,7 @@ enum iio_chan_info_enum {
 	IIO_CHAN_INFO_DEBOUNCE_COUNT,
 	IIO_CHAN_INFO_DEBOUNCE_TIME,
 	IIO_CHAN_INFO_CALIBEMISSIVITY,
+	IIO_CHAN_INFO_OVERSAMPLING_RATIO,
 };
 
 enum iio_shared_by {