TL;DR:
1. xrandr --listproviders
2. xrandr xrandr --setprovideroutputsource 1 0
3. xrandr --output HDMI-1-2 --auto
Background Ramble
So I had my system running nicely on both Windows and Linux (Debian GNU/Linux 8 with KDE), triple monitors all running off my GTX1080. Along comes Oculus and changes their implementation so you can only use “Desktop Pull-out” if you have less than 3 monitors plugged in. Fixed that by moving one of my monitors onto the integrated GPU; I only need my main monitor on the NVidia card for gaming.
This also meant moving monitors around on the outputs so that my main monitor would display the BIOS etc. (the side monitors are rotated 90 degrees).
Not surprisingly Linux needed some post-bootup configuration, and somewhat surprisingly it took quite a bit of searching to find the magic invocations this time around. The magic program itself is xrandr, nobody should be using an Xorg.conf in this day and age.
Step 1 – List Providers
First things, listing the number of “providers” (ie, graphics cards) in your system:
xrandr --listproviders
Providers: number : 2 Provider 0: id: 0x1fb cap: 0x1, Source Output crtcs: 4 outputs: 8 associated providers: 1 name:NVIDIA-0 Provider 1: id: 0x45 cap: 0x2, Sink Output crtcs: 3 outputs: 3 associated providers: 1 name:modesetting
If this doesn’t show you your cards, you have to do further digging, for example, the integrated GPU might be disabled in your BIOS.
Step 2 – Link Providers
Next, we have to “link” the providers together (this is the bit I had trouble finding):
xrandr xrandr --setprovideroutputsource 1 0
Step 3 – Enable Output
To get a list of possible output ports, use the following:
xrandr -q
Screen 0: minimum 8 x 8, current 3610 x 1680, maximum 32767 x 32767
DVI-D-0 disconnected (normal left inverted right x axis y axis)
HDMI-0 disconnected (normal left inverted right x axis y axis)
DP-0 disconnected (normal left inverted right x axis y axis)
DP-1 connected 1050x1680+0+0 right (normal left inverted right x axis y axis) 474mm x 296mm
1680x1050 59.95*+
1440x900 59.89
1400x1050 59.98
1360x765 60.00
1280x1024 75.02 60.02
1280x960 60.00
1280x720 60.00 50.00
1152x864 75.00
1024x768 75.03 70.07 60.00
800x600 75.00 72.19 60.32 56.25
720x576 50.00
720x480 59.94
640x480 75.00 72.81 59.94
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
DP-4 connected primary 2560x1440+1050+0 (normal left inverted right x axis y axis) 597mm x 336mm
2560x1440 143.86*+ 119.88 99.90 59.95
1920x1080 60.00 59.94 50.00
1440x900 59.89
1440x576 50.00
1440x480 59.94
1366x768 59.79
1280x1024 75.02 60.02
1280x720 59.94 50.00
1152x864 75.00
1024x768 75.03 70.07 60.00
800x600 75.00 72.19 60.32 56.25
720x576 50.00
640x480 75.00 72.81 59.94
DP-5 disconnected (normal left inverted right x axis y axis)
DP-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-1 connected (normal left inverted right x axis y axis)
1680x1050 59.95 +
1400x1050 59.95
1280x1024 75.02 60.02
1440x900 59.90
1280x960 60.00
1360x768 59.80
1152x864 75.00
1280x720 60.00 50.00 59.94
1024x768 75.03 70.07 60.00
832x624 74.55
800x600 72.19 75.00 60.32 56.25
720x576 50.00
720x480 60.00 59.94
640x480 75.00 72.81 66.67 60.00 59.94
720x400 70.08
HDMI-1-2 disconnected (normal left inverted right x axis y axis)
1680x1050 (0x46) 146.250MHz -HSync +VSync
h: width 1680 start 1784 end 1960 total 2240 skew 0 clock 65.29KHz
v: height 1050 start 1053 end 1059 total 1089 clock 59.95Hz
1280x1024 (0x48) 135.000MHz +HSync +VSync
h: width 1280 start 1296 end 1440 total 1688 skew 0 clock 79.98KHz
v: height 1024 start 1025 end 1028 total 1066 clock 75.02Hz
1280x1024 (0x49) 108.000MHz +HSync +VSync
h: width 1280 start 1328 end 1440 total 1688 skew 0 clock 63.98KHz
v: height 1024 start 1025 end 1028 total 1066 clock 60.02Hz
1280x960 (0x4b) 108.000MHz +HSync +VSync
h: width 1280 start 1376 end 1488 total 1800 skew 0 clock 60.00KHz
v: height 960 start 961 end 964 total 1000 clock 60.00Hz
1152x864 (0x4d) 108.000MHz +HSync +VSync
h: width 1152 start 1216 end 1344 total 1600 skew 0 clock 67.50KHz
v: height 864 start 865 end 868 total 900 clock 75.00Hz
1280x720 (0x4e) 74.250MHz +HSync +VSync
h: width 1280 start 1390 end 1430 total 1650 skew 0 clock 45.00KHz
v: height 720 start 725 end 730 total 750 clock 60.00Hz
1280x720 (0x4f) 74.250MHz +HSync +VSync
h: width 1280 start 1720 end 1760 total 1980 skew 0 clock 37.50KHz
v: height 720 start 725 end 730 total 750 clock 50.00Hz
1024x768 (0x51) 78.750MHz +HSync +VSync
h: width 1024 start 1040 end 1136 total 1312 skew 0 clock 60.02KHz
v: height 768 start 769 end 772 total 800 clock 75.03Hz
1024x768 (0x52) 75.000MHz -HSync -VSync
h: width 1024 start 1048 end 1184 total 1328 skew 0 clock 56.48KHz
v: height 768 start 771 end 777 total 806 clock 70.07Hz
1024x768 (0x53) 65.000MHz -HSync -VSync
h: width 1024 start 1048 end 1184 total 1344 skew 0 clock 48.36KHz
v: height 768 start 771 end 777 total 806 clock 60.00Hz
800x600 (0x55) 50.000MHz +HSync +VSync
h: width 800 start 856 end 976 total 1040 skew 0 clock 48.08KHz
v: height 600 start 637 end 643 total 666 clock 72.19Hz
800x600 (0x56) 49.500MHz +HSync +VSync
h: width 800 start 816 end 896 total 1056 skew 0 clock 46.88KHz
v: height 600 start 601 end 604 total 625 clock 75.00Hz
800x600 (0x57) 40.000MHz +HSync +VSync
h: width 800 start 840 end 968 total 1056 skew 0 clock 37.88KHz
v: height 600 start 601 end 605 total 628 clock 60.32Hz
800x600 (0x58) 36.000MHz +HSync +VSync
h: width 800 start 824 end 896 total 1024 skew 0 clock 35.16KHz
v: height 600 start 601 end 603 total 625 clock 56.25Hz
720x576 (0x59) 27.000MHz -HSync -VSync
h: width 720 start 732 end 796 total 864 skew 0 clock 31.25KHz
v: height 576 start 581 end 586 total 625 clock 50.00Hz
720x480 (0x5b) 27.000MHz -HSync -VSync
h: width 720 start 736 end 798 total 858 skew 0 clock 31.47KHz
v: height 480 start 489 end 495 total 525 clock 59.94Hz
640x480 (0x5c) 31.500MHz -HSync -VSync
h: width 640 start 656 end 720 total 840 skew 0 clock 37.50KHz
v: height 480 start 481 end 484 total 500 clock 75.00Hz
640x480 (0x60) 25.175MHz -HSync -VSync
h: width 640 start 656 end 752 total 800 skew 0 clock 31.47KHz
v: height 480 start 490 end 492 total 525 clock 59.94Hz
And then just try enabling each one in turn:
xrandr --output HDMI-1-1 --auto
And bingo, hopefully your display(s) will pop up.
