+/**
+ * struct ff_effect - defines force feedback effect
+ * @type: type of the effect (FF_CONSTANT, FF_PERIODIC, FF_RAMP, FF_SPRING,
+ * FF_FRICTION, FF_DAMPER, FF_RUMBLE, FF_INERTIA, or FF_CUSTOM)
+ * @id: an unique id assigned to an effect
+ * @direction: direction of the effect
+ * @trigger: trigger conditions (struct ff_trigger)
+ * @replay: scheduling of the effect (struct ff_replay)
+ * @u: effect-specific structure (one of ff_constant_effect, ff_ramp_effect,
+ * ff_periodic_effect, ff_condition_effect, ff_rumble_effect) further
+ * defining effect parameters
+ *
+ * This structure is sent through ioctl from the application to the driver.
+ * To create a new effect aplication should set its @id to -1; the kernel
+ * will return assigned @id which can later be used to update or delete
+ * this effect.
+ *
+ * Direction of the effect is encoded as follows:
+ * 0 deg -> 0x0000 (down)
+ * 90 deg -> 0x4000 (left)
+ * 180 deg -> 0x8000 (up)
+ * 270 deg -> 0xC000 (right)