As the title says...I have a Radeon HD 7990 and I'm using the open source drivers. The problem is IDK if it is possible to enable xfire. If anyone can give me some advice on how to go about this, that would be great!
Hardware passthrough is probably the way you'll want to go
Iirc you need the proprietary drivers for xfire
It's been around six months since I tried but I could never get Crossfire to work when I was running a pair of 7970's even with the proprietary drivers. It would say it was working but the second card would just sit there cold and unused.