The Lenovo *40 series introduced a new type of touchpad. Previously, all
laptops had a separate set of physical buttons for the
series removed these buttons, relying on a software emulation of the top
section of the touchpad. This is visually marked on the trackpad itself,
and clicks can be triggered by pressing the touchpad down with a finger in
the respective area:
The size of the buttons matches the visual markings on this touchpad.
The width of the left and right buttons is approximately 42% of the
touchpad’s width, the middle button is centered and assigned 16% of the
The line of the buttons is 5mm from the top edge of the touchpad,
measurements of button presses showed that the size of the buttons needs to
be approximately 10mm high to work reliable (especially when using the
thumb to press the button).
Movement in the top button area does not generate pointer movement. These
buttons are not replacement buttons for the bottom button area but have
their own behavior. Semantically attached to the trackstick device, libinput
re-routes events from these buttons to appear through the trackstick device.
The top button areas work even if the touchpad is disabled but will be
disabled when the trackstick device is disabled. If the finger starts inside
the top area and moves outside the button area the finger is treated as dead
and must be lifted to generate future buttons. Likewise, movement into the
top button area does not trigger button events, a click has to start inside
this area to take effect.
The firmware on the first generation of touchpads providing top software
buttons is buggy and announces wrong ranges.
Kernel patches are required;
these fixes are available in kernels 3.14.1, 3.15 and later but each
touchpad needs a separate fix.
The October 2014 refresh of these laptops do not have this firmware bug
anymore and should work without per-device patches, though
this kernel commit
For a complete list of supported touchpads check
the kernel source
(search for “topbuttonpad_pnp_ids”).