3 Monitor PCI-e Graphics card on Linux (without tremendous pain)?
I believe that you need to have one of the displays connected through an active adapter, as the cards that are on sale today do not have enough power to support 3 displays at once (power-wise); or to be more specific, with the exception of some models, they don't have the necessary hardware to power 3 ports.
The following forum threads may provide more insight:
- http://forums.amd.com/game/messageview.cfm?catid=260&threadid=123437
- http://forums.anandtech.com/showthread.php?t=2047517
- http://www.tomshardware.co.uk/forum/282164-15-5750-monitor-extend-desktop
The latter two are well known hardware focused websites, so they should be reasonably reliable (considering them being forums and not official articles). However please note that I don't have an ATI Eyefinity-capable card, nor have I tried this kind of thing under GNU/Linux yet. I'm only sharing what I've read elsewhere in the past, hoping that it can guide you in the right direction (or that somebody else confirms it).
Edit:
The following support article claims that 3+ monitor configurations require to have the extra monitors on top of the base two connected via DisplayPort:
- http://support.amd.com/us/kbarticles/Pages/gpu50-ati-eyefinity-display-configs.aspx (scroll down to the "Monitors" section)
- http://blogs.amd.com/play/2010/08/30/ati-eyefinity-validated-ready-not-a-just-a-logo-an-experience-part-3/ (scroll down to bottom note 1)
You mentioned that you have the monitors plugged-in via 2 DVI and 1 HDMI ports. Do you have the option to try switching one of them to DisplayPort and giving it a try?
Maximum two monitors can be enabled at the same time over the DVI and HDMI ports.
To use three monitors, at least one of them must use the DisplayPort.
From AMD Eyefinity FAQ:
How many non-DisplayPort monitors can I use with an AMD Eyefinity technology-enabled graphics card?
You can connect up to two non-DisplayPort monitors at one time to an AMD Eyefinity technology-enabled graphics card using non-DisplayPort connections or passive DisplayPort dongles. To enable and drive 3 or more non-DisplayPort monitors at one time, the additional non-DisplayPort monitors must be connected with an active DisplayPort dongle.
AMD also has a list of working adapters for running non-DisplayPort monitors off a DisplayPort.
On Linux support
A post on phoronix.com says that AMD has Eyefinity support for Linux from driver version 10.7 of July 2010, and that Ubuntu 10.04 has "production support".
However, the AMD Eyefinity FAQ merely says that
There are plans for Linux support in an upcoming update to AMD Catalyst™ software
and the official ADM Eyefinity Technology page says (tiny font at the bottom) that
ATI Eyefinity technology can support up to 6 displays using a single enabled ATI Radeon™ graphics card with Windows Vista or Windows 7...
ATI Eyefinity technology can support multiple displays using a single enabled ATI FirePro™ professional graphics card... Microsoft® Windows® 7, Windows Vista®, or Linux® is required in order to support more than 2 displays.
So the official stance seems to be that multiple displays for Linux is only supported for their professional cards.
The Unofficial AMD Linux wiki says in an entry added December 2010:
The proprietary driver supports more than two simultaneous outputs on HD5xxx cards having more than two physical independant out...
EyeFinity support is still messy