I’m having similar problem right now, with Qt5… Here’s the only thing that I’ve found: link [developer.qt.nokia.com]

There’s not much documentation on QPA/Lighthouse in Qt 4.8. But the process basically goes like this:

1) Get the Qt library compiling for your platform.
2) Get the ‘minimal’ plugin building for your platform.
3) Build a Qt example app (eg. AnimatedTiles) for your platform and run it with the ‘minimal’ plugin.
4) Use the ‘minimal’, ‘eglfs’ and ‘xlib’ plugins as reference to start developing your own plugin.
5) Use the #qt-lighthouse channel on IRC (freenode) to speak with the QPA developers at Nokia and other developers using QPA.

Here is a little bit of (old) documentation from the Lighthouse team:

http://developer.qt.nokia.com/wiki/Getting_Started_With_Lighthouse

There is a also some documentation in the form of comments in the source files (ending _qpa) in the Qt source tree (QPA is part of GUI).