AMD's Alex Deucher has just committed initial support for Embedded DisplayPort (eDP) connectors/monitors to the xf86-video-ati DDX display driver. Traditional DisplayPort monitors are already supported by this open-source ATI driver, but now Embedded DisplayPort connectors should begin to work as well. Here
is the Git commit that provides the initial support.
Alex has also published a set of patches
that allows Embedded DisplayPort to work with ATI kernel mode-setting too.