I'm currently running ubuntu with dwm on my macbook air and I have a problem. When I connect to a monitor using a dongle, which converts an HDMI cable to MBA's DP port, xrandr still recognizes it as HDMI.
When I try to connect to it as such it just shows a pure green screen, presumably because it is trying to feed HDMI through a DP port.
That said, usually this isn't a problem. When I use the Gnome displays tool it's able to correctly handle this. So basically my question is, how can I tell xrandr to send DP even though it's convinced that it's connected to HDMI?