Arch Linux

doorknob60

Member

Registered: 2008-09-29

Posts: 404

Can't get 4 monitors across 2 GPUs to work

I have a system with 2 GPUs (really it's one physical PCIe card, but I guess it's really 2 GPUs seen by the OS), each with 2 monitors connected to it. These are the GPUs:

$ lspci|grep VGA
04:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV620 LE [Radeon HD 3450]
05:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV620 LE [Radeon HD 3450]

I'm using the open source drivers. In Debian Stable with Catalyst (old version, no longer works with new kernel/Xorg) I'm able to get this setup working with Xinerama, although performance is sub-par. It also works fine in Windows.

When I start X with the default config, only two of my monitors show up, and they both work as expected. If I run this command:

xrandr --setprovideroutputsource 1 0

Then all 4 monitors show up, like this:

$ xrandr
Screen 0: minimum 320 x 200, current 4640 x 1080, maximum 8192 x 8192
DVI-0 connected 1280x1024+3360+0 (normal left inverted right x axis y axis) 338mm x 270mm
   1280x1024     60.02*+  75.02  
   1152x864      75.00  
   1024x768      75.08    60.00  
   800x600       75.00    60.32  
   640x480       75.00    60.00  
   720x400       70.08  
DVI-1 connected 1440x900+1920+0 (normal left inverted right x axis y axis) 408mm x 255mm
   1440x900      59.89*+  74.98                                                
   1280x1024     75.02    60.02                                                
   1280x800      59.91                                                         
   1152x864      75.00                                                         
   1024x768      75.08    70.07    60.00                                       
   832x624       74.55                                                         
   800x600       72.19    75.00    60.32    56.25                              
   640x480       75.00    72.81    66.67    60.00                              
   720x400       70.08                                                         
DVI-1-2 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 477mm x 268mm                                                                      
   1920x1080     60.00*+                                                       
   1600x1200     60.00                                                         
   1680x1050     59.88                                                         
   1400x1050     59.95                                                         
   1600x900      59.98                                                         
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x800      59.91  
   1152x864      75.00  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    66.67    60.00  
   720x400       70.08  
DVI-1-3 connected (normal left inverted right x axis y axis)
   1440x900      59.89 +  74.98  
   1280x1024     75.02    60.02  
   1280x800      59.91  
   1152x864      75.00  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    66.67    60.00  
   720x400       70.08  

The problem is, I can only use 3 at a time before it no longer works properly. I want to have all 4 side by side. If I enable all 4 at once, no matter what settings I use to enable it, the left two monitors are just overlapping each other, rather than 4 separate screens. It almost seems like I'm running into a hardware limitation, but I know that it works with Catalyst and in Windows, so the hardware is capable of it. I feel like using xrandr --setprovideroutputsource is maybe only using 1 of the GPUs to render everything, and it can't handle it (though not sure exactly how that work), and maybe that's the issue. I've tried using Xinerama but I can't get Xorg to start when I have it enabled in an Xorg.conf.  Any ideas? I still have my Debian installation working, but as soon as the current version of Debian is unsupported I'm gonna have to upgrade, meaning I need to make this work with the Open Source Drivers somehow.

Here is what I mean by overlapping. I run this command, which theoretically should give me my desired setup:

xrandr --output DVI-1 --mode 1440x900 --pos 3360x0 --rotate normal --output DVI-0 --mode 1280x1024 --pos 4800x0 --rotate normal --output DVI-1-3 --mode 1440x900 --pos 0x0 --rotate normal --output DVI-1-2 --mode 1920x1080 --pos 1440x0 --rotate normal

But then, the left monitor is overlapping part of the 2nd-to-left monitor (the far right 2 are fine, you don't see them in the picture).

You can see in arandr, that the layout is configured properly, but really it's not working right.

Last edited by doorknob60 (2014-11-19 21:54:23)