iio: core: Introduce IIO_VELOCITY and IIO_MOD_ROOT_SUM_SQUARED_X_Y_Z

Some devices export the current speed value of the user.

One of this devices is Freescale's MMA9553L
(http://www.freescale.com/files/sensors/doc/ref_manual/MMA9553LSWRM.pdf)
that computes the speed of the user based on the number of steps and
stride length.

Introduce a new channel type VELOCITY and a modifier for the magniture or
norm of the velocity vector, IIO_MOD_ROOT_SUM_SQUARED_X_Y_Z.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio

@@ -295,6 +295,7 @@ What:		/sys/bus/iio/devices/iio:deviceX/in_rot_from_north_true_tilt_comp_scale
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressureY_scale
 What:		/sys/bus/iio/devices/iio:deviceX/in_pressure_scale
 What:		/sys/bus/iio/devices/iio:deviceX/in_humidityrelative_scale
+What:		/sys/bus/iio/devices/iio:deviceX/in_velocity_sqrt(x^2+y^2+z^2)_scale
 KernelVersion:	2.6.35
 Contact:	linux-iio@vger.kernel.org
 Description:
@@ -1164,3 +1165,12 @@ Contact:	linux-iio@vger.kernel.org
 Description:
 		This attribute is used to read the number of steps taken by the user
 		since the last reboot while activated.
+
+What:		/sys/.../iio:deviceX/in_velocity_sqrt(x^2+y^2+z^2)_input
+What:		/sys/.../iio:deviceX/in_velocity_sqrt(x^2+y^2+z^2)_raw
+KernelVersion:	3.19
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This attribute is used to read the current speed value of the
+		user (which is the norm or magnitude of the velocity vector).
+		Units after application of scale are m/s.

drivers/iio/industrialio-core.c

@@ -74,6 +74,7 @@ static const char * const iio_chan_type_name_spec[] = {
 	[IIO_STEPS] = "steps",
 	[IIO_ENERGY] = "energy",
 	[IIO_DISTANCE] = "distance",
+	[IIO_VELOCITY] = "velocity",
 };
 
 static const char * const iio_modifier_names[] = {
@@ -99,6 +100,7 @@ static const char * const iio_modifier_names[] = {
 	[IIO_MOD_JOGGING] = "jogging",
 	[IIO_MOD_WALKING] = "walking",
 	[IIO_MOD_STILL] = "still",
+	[IIO_MOD_ROOT_SUM_SQUARED_X_Y_Z] = "sqrt(x^2+y^2+z^2)",
 };
 
 /* relies on pairs of these shared then separate */

include/linux/iio/types.h

@@ -34,6 +34,7 @@ enum iio_chan_type {
 	IIO_STEPS,
 	IIO_ENERGY,
 	IIO_DISTANCE,
+	IIO_VELOCITY,
 };
 
 enum iio_modifier {
@@ -68,6 +69,7 @@ enum iio_modifier {
 	IIO_MOD_JOGGING,
 	IIO_MOD_WALKING,
 	IIO_MOD_STILL,
+	IIO_MOD_ROOT_SUM_SQUARED_X_Y_Z,
 };
 
 enum iio_event_type {