The Lenovo Yoga 900 trackpad and touchscreen do not work with the default kernel. I've upgraded to 4.4-rc7 to get the latest changes, but this version still doesn't have the correct drivers.
A workaround has been created, which requires a custom kernel compilation. It would be nice if the hardware works with the default kernel though.
Here is the initial fix that lead to a workaround.
Here is an article I created to help others using Ubuntu.
*** This bug has been marked as a duplicate of bug 108581 ***