Currently it seems that in order for the linux driver to load you need a monitor attached. You could trick your linux system into thinking a monitor is attached using a dummy vga adapter. Another possible thing to consider is that the device section in xorg.conf may not be invoked unless a screen somehow references it.
No, it just wouldnt work. I think it should work without the monitor with newer drivers(I had a monitor attached nevertheless). But what I had as a problem this time was segmentation faults when I get both nvidia and amd/ati drivers loaded. (fglrx caused X to do segmentation fault).
Luckily the solution was simple. I removed the radeon and used nvidia cards only. It is extremely difficult to run opencl programs on AMD/ATI cards, in my opinion if they dont fix it there is not much of a point of optimizing HPC applications for AMD/ATI platforms using OpenCL since you will never see these cards in supercomputers. But thats my opinion... anyway... I hope they would fix these problems!
Normally you'd just have to list the devices in your /etc/X11/xorg.conf. For example in my xorg.conf I have the following three devices:
You can find the BusID by running the lspci command and looking for your graphics devices. When you add your devices to the xorg.conf they should be running after you restart your x server.
OK. I tried this several times but X does not load the driver properly unless if the card into serverlayout and say that there is a screen connected. I am not sure if I am doing something wrong or not. It would be great if somebody would copy/paste a working configuration. I am not even able to get this working between 2 radeon cards.