Over a year ago, I was able to simultaneously use 3 external displays from my Linux desktop (Ubuntu 14.04), running on a i7-6700K (HD530 graphics) CPU. I have 3 monitors, connecting an LG ultra-wide 3440x1440@60Hz via DP, connecting a Dell 1920x1200@60Hz via HDMI, and connecting a Sony TV (native resolution is 4k) at 4k or 1920x1080@30Hz using DVI (through a DVI->HDMI converter).
However, after I upgraded the CPU from 6700K to 7700K (HD630), with the intel graphics driver in the Linux kernel (4.3 series and 4.4 series), I was not able to get the 3rd video output (to the Sony TV via DVI) anymore. I recently upgraded my Linux to 16.04 and the kernel from 4.4 to 4.15 (using HWE kernel line), and was hoping that I can get the 3rd display back, but still, xrandr -q does not show me the 3rd output even it is connected. However, according to this page, 3-display is supposed to be supported for HD630
I am wondering if Intel dropped the support for triple external display support on Linux? if not, what is the correct kernel version that supports this? or this is an hardware limitation (630 vs 530?) I also reported this to Ubuntu as a bug, but there was no reply or activity
My current xrandr -q output is listed below:
fangq@taote:~$ xrandr -q Screen 0: minimum 320 x 200, current 5360 x 1440, maximum 8192 x 8192 DP1 connected primary 3440x1440+1920+0 (normal left inverted right x axis y axis) 800mm x 335mm 3440x1440 59.97*+ 49.99 29.99 2560x1080 60.00 1920x1080 60.00 59.94 1680x1050 59.95 1600x900 60.00 1280x1024 60.02 1280x800 59.81 1152x864 59.97 1280x720 60.00 59.94 1024x768 60.00 800x600 60.32 720x480 60.00 59.94 640x480 60.00 59.94 HDMI1 disconnected (normal left inverted right x axis y axis) HDMI2 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm 1920x1200 59.95*+ 1920x1080 60.00 50.00 59.94 30.00 25.00 24.00 29.97 23.98 1920x1080i 60.00 50.00 59.94 1600x1200 60.00 1280x1024 75.02 60.02 1152x864 75.00 1280x720 60.00 50.00 59.94 1024x768 75.03 60.00 800x600 75.00 60.32 720x576 50.00 720x576i 50.00 720x480 60.00 59.94 720x480i 60.00 59.94 640x480 75.00 60.00 59.94 720x400 70.08 HDMI3 disconnected (normal left inverted right x axis y axis)