I have an AMD W9100 card and 6 identical 1920x1080/60Hz DVI monitors.
I have an Ubuntu server 14.04, running fglrx 15.201 and would like to understand the requirements for using active vs. passive adapters.
My xorg.conf (attached) is set up with 6 monitors, each rotated "left". Each monitor after the first one has an offset of 1090 pixels from the previous monitor (10px for bezel compensation).
Now, using passive miniDP - DVI adapters, only 3 monitors get signal. It doesn't matter which combination of outputs I use, the total number of displays receiving a signal stays at 3. I have verified that the pixel offset for each output is correct.
If I connect 3 displays with passive adapters and 1 display with an active adapter, all 4 displays receive signal.
Connecting all 6 displays with 6 active adapters also works fine.
Why is this? I have watched the old video here: http://support.amd.com/en-us/search/faq/154 but there are some discrepancies with the AMD documentation.
Please take a look at page 9 of the AMD W9100 manual: https://www.amd.com/Documents/AMD_Firepro_W9100_User_Guide.pdf
It is stated, that 6 single-link DVI monitors can be connected to the card by using 6 passive miniDP - DVI adapters. This is not what I'm experiencing, as I need to use active adapters to get a signal to displays 4, 5, and 6.
To stir this up even more, a client of mine states that they were able to get all 6 displays working with passive adapters on Ubuntu Desktop 14.04.
Is this a driver issue? Maybe some kind of artificial limitation in fglrx when not running a desktop manager? Am I just missing a configuration option in my xorg.conf to enable all-passive adapters? I'm running out of ideas.