Hi everyone,
You will not imagine how I spend my weekend... Actually, how I lost my weekend!
Part of my plan to use computing power to warm-up my place, I had on my do to list to make my two Radeon HD7990 crunching data for some community research projects. As the fglrx driver (the one enabling Open CL for the Radeon graphic cards) is not supported anymore by Ubuntu 16.04 (which I had on my computer), I tried to install the AMDGPU-PRO driver. What looked to be a trivial task, ended up eating hours of heavy debug. .. my mistake, as I did not read properly the release note of the AMD driver. The AMDGPU-PRO is the AMD proprietary driver, working with the latest releases of Ubuntu, having support for most for the AMD GPU cards, ... except my HD7900 series.
Once I realized the lack of support for my graphic cards, I downgraded my system to Ubuntu 14.04, the last known release to allow the installation of the fglrx driver. But this proved to be a disaster, crushing the xorg-server. I spent lot of time searching on the internet, and I even downgraded the xorg-server to version 1.16 (which was known as the last stable version working with the fglrx driver). I ended up re-installing Ubuntu 14.04 several times, but all my effort ended up in bring it to a very unstable OS.
Now, my only hope is to go to an even older Ubuntu (I just prepared a USB stick with Ubuntu 12.04), but this makes me nervous, as the 12.04 does not get anymore security updates.