iio: core: Introduce CHANGE event type

A step detector will generate an interrupt each time N step are detected.
A device that has such pedometer functionality is Freescale's MMA9553L:
http://www.freescale.com/files/sensors/doc/ref_manual/MMA9553LSWRM.pdf.

Introduce IIO_EV_TYPE_CHANGE event type for events that are generated
when the channel passes a threshold on the absolute change in value.
Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -891,12 +891,24 @@ Description:
 		number or direction is not specified, applies to all channels of
 		this type.
 
-What:		/sys/.../events/in_steps_instance_en
-KernelVersion:	3.19
+What:		/sys/.../events/in_steps_change_en
+KernelVersion:	3.20
 Contact:	linux-iio@vger.kernel.org
 Description:
-		Enables or disables step detection. Each time the user takes a step an
-		event of this type will be generated.
+		Event generated when channel passes a threshold on the absolute
+		change in value. E.g. for steps: a step change event is
+		generated each time the user takes N steps, where N is set using
+		in_steps_change_value.
+
+What:		/sys/.../events/in_steps_change_value
+KernelVersion:	3.20
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Specifies the value of change threshold that the
+		device is comparing against for the events enabled by
+		<type>[Y][_name]_roc[_rising|falling|]_en. E.g. for steps:
+		if set to 3, a step change event will be generated every 3
+		steps.
 
 What:		/sys/bus/iio/devices/iio:deviceX/trigger/current_trigger
 KernelVersion:	2.6.35

drivers/iio/industrialio-event.c

@@ -198,6 +198,7 @@ static const char * const iio_ev_type_text[] = {
 	[IIO_EV_TYPE_THRESH_ADAPTIVE] = "thresh_adaptive",
 	[IIO_EV_TYPE_MAG_ADAPTIVE] = "mag_adaptive",
 	[IIO_EV_TYPE_INSTANCE] = "instance",
+	[IIO_EV_TYPE_CHANGE] = "change",
 };
 
 static const char * const iio_ev_dir_text[] = {

drivers/staging/iio/Documentation/iio_event_monitor.c

@@ -60,6 +60,7 @@ static const char * const iio_ev_type_text[] = {
 	[IIO_EV_TYPE_THRESH_ADAPTIVE] = "thresh_adaptive",
 	[IIO_EV_TYPE_MAG_ADAPTIVE] = "mag_adaptive",
 	[IIO_EV_TYPE_INSTANCE] = "instance",
+	[IIO_EV_TYPE_CHANGE] = "change",
 };
 
 static const char * const iio_ev_dir_text[] = {
@@ -179,6 +180,7 @@ static bool event_is_known(struct iio_event_data *event)
 	case IIO_EV_TYPE_THRESH_ADAPTIVE:
 	case IIO_EV_TYPE_MAG_ADAPTIVE:
 	case IIO_EV_TYPE_INSTANCE:
+	case IIO_EV_TYPE_CHANGE:
 		break;
 	default:
 		return false;

include/linux/iio/types.h

@@ -79,6 +79,7 @@ enum iio_event_type {
 	IIO_EV_TYPE_THRESH_ADAPTIVE,
 	IIO_EV_TYPE_MAG_ADAPTIVE,
 	IIO_EV_TYPE_INSTANCE,
+	IIO_EV_TYPE_CHANGE,
 };
 
 enum iio_event_info {