/**
@page t440_support Lenovo *40 series touchpad support

@section t440_support_overview Overview

The Lenovo *40 series introduced a new type of touchpad. Previously, all
laptops had a separate set of physical buttons for the
<a href="http://en.wikipedia.org/wiki/Pointing_stick">trackstick</a>. This
series removed these buttons, relying on a software emulation of the top
section of the touchpad. This is visually marked on the trackpad itself,
approximately like this:

@dot
digraph G {
  subgraph cluster_0 {
    margin="0";

    clickpad [
      shape = "record";
      color = "none";
    label = "{{LLLLLLLLLL|MMMMM|RRRRRRRRR}|\n\n\n\n\n\n\n\n|{LLLLLLLL|          |RRRRRRRR}}";
    ]
  }
}
@enddot

The below is a list of what is needed for support of these devices. This page
only covers the top software buttons, the bottom button behavior is covered in
@ref clickpad_softbuttons "Clickpad software buttons".

@section t440_support_btn_size Size of the buttons

The approximate size of the top software buttons is 8% of the touchpad's
announced range, starting from the top. Note that a
<a href="https://lkml.org/lkml/2014/3/7/722">kernel patch</a> is required to
get the right ranges.

The size of the left and right buttons is approximately 42%, the middle button
is centered and should be assigned approximately 16% of the touchpad width.

@section t440_support_btn_behavior Button behavior

Movement in the top button area must not generate pointer movement, these
buttons are not replacement buttons for the bottom area but have their own
behaviour. They do not work for click-and-drag.

If the finger starts inside the top area and moves outside the button area
without the physical button being down, movement may start.

Movement into the top button area should not trigger button events, a click
has to start inside this area to take effect.

The top button areas must work, even if the touchpad is otherwise disabled
(e.g. by a disable-while-typing feature).

@section t440_support_identification Identification

The touchpads can be identified by the PNPID, or by a DMI match

- Helix: PnPID: <b>LEN0033</b>, DMI substring match <em>"Helix"</em>
- T540: PnPID: <b>LEN0034</b>, DMI substring match <em>"T540?"</em>
- x240: PnPID: <b>LEN0035</b>, DMI substring match <em>"X240"</em>
- T440: PnPID: <b>LEN0036</b>, DMI substring match <em>"T440?"</em>
- Yoga: PnPID: <b>LEN0042</b>, DMI subString match <em>"S1Yoga"</em>

*/