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Graphics Cards

Journeyman III

Question about using Two GPUs for Dual Monitor on Linux

I have two monitors, one accepts DisplayPort and the other only VGA, and my GPU is a Radeon Pro Wx 4100. I used an adapter to connect my VGA monitor, but because it would not be recognized on boot, I had to manually plug it in every time I turn my computer on. Recently I remembered that I had a spare display card available, a R7-240. I've placed it in to my box and tried to boot, and this is where things get a bit odd.
The machine detects the second GPU, as does the OS. But the monitor itself is not activated. I did some searching online, and found that my card was using the older version of the AMD Open Source drivers. I added configuration that would make the system use amdgpu instead of radeon, an noticed the follow behavior from there:

-Initially, the screen still did not operate, even though the system detected the second card. I checked the x11 logs as well, and it was detected there as well.
- Using xrandr, I noted that my second card was listed as a provider, but the monitor itself was not seen, nor was a Screen profile made.

-I then used X -configre :1 to make a xorg.conf file. This actually made the monitor turn on, and become accessible...sort of. I could move my mouse to the screen, but it was otherwise blank and I could not manipulate anything there.
- Using xrandr again, the program detected the monitor, and that it was a VGA, but did not list the second card as a provider.

In addition to the above, when I changed the xorg.conf file to have the second monitor be treated as the main one, it worked just fine. It seems that the system can use both cards, but only want to use one at a time? Would anyone be knowledgeable about how I could get this working?

I am currently using MX Linux. Relevant specs are as follows:

Athlon X4 845
Radeon pro wx 4100
EVGA 500w

4 Replies




An Update:

I've been working at this during the day, and have made some progress in narrowing down the issue.

-A custom xorg.conf is necessary for this setup. Otherwise, X will turn off the monitor.
-I was able to use xinerama to stretch the first screen out, but that causes problems for many programs I am running, which rely on xrandr.
-It turns out that xrandr sees both cards, despite my earlier confusion.  Specifying whether I am referring to Screen 0 or 1 will have the program output information relevant to each card.

The problem still is that my second screen, despite being on and noticed by the system, can't be interacted with beyond moving the mouse. I can't open windows, I can't set background, it just sits there.


how about upgrading your monitor? DP monitors are not that expensive anymore. Your configuration is not officially supported nor tested.

Adept I

I didn't get into the configs, but I also had a problem with Dual GPU and two screens. The settings in xfce4-settings seemed to reset rather than lock.
My config:
AMD Kaveri 7850K driver AMDGPU, DCmode=1 + RX460