iio: Add channel for Gravity

Add new channel types support for gravity sensor.

Gravity sensor provides an application-level or physical collection that
identifies a device that measures exclusively the force of Earth's
gravity along any number of axes.

More information can be found in:
http://www.usb.org/developers/hidpage/HUTRR59_-_Usages_for_Wearables.pdf

Signed-off-by: Song Hongyan <hongyan.song@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -170,6 +170,16 @@ Description:
 		Has all of the equivalent parameters as per voltageY. Units
 		after application of scale and offset are m/s^2.
 
+What:		/sys/bus/iio/devices/iio:deviceX/in_gravity_x_raw
+What:		/sys/bus/iio/devices/iio:deviceX/in_gravity_y_raw
+What:		/sys/bus/iio/devices/iio:deviceX/in_gravity_z_raw
+KernelVersion:	4.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Gravity in direction x, y or z (may be arbitrarily assigned
+		but should match other such assignments on device).
+		Units after application of scale and offset are m/s^2.
+
 What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_x_raw
 What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_y_raw
 What:		/sys/bus/iio/devices/iio:deviceX/in_anglvel_z_raw

drivers/iio/industrialio-core.c

@@ -83,6 +83,7 @@ static const char * const iio_chan_type_name_spec[] = {
 	[IIO_ELECTRICALCONDUCTIVITY] = "electricalconductivity",
 	[IIO_COUNT] = "count",
 	[IIO_INDEX] = "index",
+	[IIO_GRAVITY]  = "gravity",
 };
 
 static const char * const iio_modifier_names[] = {

include/uapi/linux/iio/types.h

@@ -42,6 +42,7 @@ enum iio_chan_type {
 	IIO_ELECTRICALCONDUCTIVITY,
 	IIO_COUNT,
 	IIO_INDEX,
+	IIO_GRAVITY,
 };
 
 enum iio_modifier {

tools/iio/iio_event_monitor.c

@@ -57,6 +57,7 @@ static const char * const iio_chan_type_name_spec[] = {
 	[IIO_RESISTANCE] = "resistance",
 	[IIO_PH] = "ph",
 	[IIO_UVINDEX] = "uvindex",
+	[IIO_GRAVITY] = "gravity",
 };
 
 static const char * const iio_ev_type_text[] = {
@@ -149,6 +150,7 @@ static bool event_is_known(struct iio_event_data *event)
 	case IIO_RESISTANCE:
 	case IIO_PH:
 	case IIO_UVINDEX:
+	case IIO_GRAVITY:
 		break;
 	default:
 		return false;