Successful quad-head w/ Linux Mint & ATI cards...
 

Over a year ago I posted a thread asking for help getting multiple graphics cards working on a multi-head setup. I actually got this resolved quite some time ago and I never had to resort to using Windows.

The original hardware was an ATI Radeon HD 5750 and two older Matrox cards which I attempted to use with 4 monitors. The Matrox cards were a no-go. Too old. The last Kernel they supported was pre 2.6. A damn shame, since each one is capable of supporting 4 VGA inputs. I had to scour the internet to find them and the 4x-VGA adapters.

Instead, I raided an e-waste bin in the parking garage of an office building and scored this spread...
http://www.weareready.ru/img/allcards.jpg

After extensive trials with different combinations, I discovered that it's best to use all cards of the same brand together. I chose the two red cards in the bottom right, along with the existing Radeon. All ATI.

01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Juniper PRO [Radeon HD 5750]
03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV530 GL [FireGL V3400]
04:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV370 GL [FireGL V3100] (rev 80)


So now I have 4 monitors connected to 3 ATI cards...
http://www.weareready.ru/img/setup-late2016.jpg
And could potentially attach two more to the cards on PCIe 3 and 4.

I did not have to use proprietary drivers or anything. ATI is apparently very good for that on Linux. 3dfx and videos work fine when dragged from screen to screen, across cards. The only difficulty was figuring out the right ports to use. The upper screen is 40" 1920x1080, while the three on the bottom are all 20/21" 1440x900, 1280x1024 and 1024x1280 (rotated).

The 40" and rotated screen had to be put on the Radeon, but the two FireGL cards handle the non-rotated screens just fine. Sometimes when Mint starts up, the display is messed up (screens only show a sliver or not at all), but restarting Cinnamon (CTRL-ALT-ESC) and NOT clicking OK on a dialog saying: "CRT-XX could not be configured..." fixes the issue. I believe it is related to incorrect or duplicate config files, but I rarely hard-boot so I have not looked into it.

For anyone who runs dual-head right now, quad head is like 2x better I have to tell you. Being able to just look over to the side at a reference or keep your toolbars out of the way... It's definitely worth the hassle. But you need an awesome desk to make it work. I built mine.

So for anyone looking for a sweet multi-monitor setup...

- Get a motherboard with lots of PCI slots. Mine has [ 1x, 16x, 8x, 8x, PCI, 4x ]
- Get several cards of the same brand. Mine are all ATI, all different models and 6 years apart.
- Put rotated screens on your primary / newest card.
- Get some zip-ties because it's going to be a rat's nest back there :) ...