Unable to use three 4K screens (HDMI 2.0 issues)

[JLoec]

According to the support page https://www.intel.com/content/www/us/en/support/articles/000005571/mini-pcs.html "Setting Up Multiple Displays for the Intel® NUC", the NUC6i7KYK should be able to support three 4K screens.

I'm using Ubuntu 18.04 running Linux kernel 4.15.0-20

I'm using three LG 27UD68P-B screens (With "Super Resolution+" and "HDMI UHD Deep Color" enabled):

1. Using the USB-C output " Displayport
2. Using the miniDP " Displayport
3. And the last one using a HDMI 2.0 cable from the HDMI output " HDMI input

As soon as I attach the HDMI cable things start going wrong, but each environment goes wrong a bit differently:

• In GDM3 (the login manager) All 3 screens actually work! At 60Hz even. And I get no jitter or image corruptions.
• When logging into Gnome Shell, only the HDMI screen will work, dragging any window will cause some mosaïque-like corruption (video below).
• Gnome Shell using Wayland just refuses to open.
• The Ubuntu MATE desktop interface will just mirror all 3 displays, attempting to change this will cause all 3 screens to be garbled.
• Even using the HDMI screen at a LOWER resolution (like regular 1080p) will cause the mosaïque issue.

So how can I solve this?

[idata]

Hello skerit,

Thank you for joining the Intel Community Support.Intel does not test and validate Intel® NUC on Linux. However, we know that a lot of Intel® NUC owners are using it successfully on many different Linux distros. I recommend you to check your Linux distro's website and forums for peer assistance with this inquiry.Additionally, you may visit the following website: https://01.org/linuxgraphicsWanner G.

[JLoec]

I was afraid of that But just to make sure: the device should be able to use three 4K screens, right?

[idata]

Hello skerit,

You are right. The Intel® NUC Kit NUC6i7KYK supports three 4K displays, but you have to connect one display per video port. As you already mentioned, the following configuration is recommended under Triple Display Configurations: https://www.intel.com/content/www/us/en/support/articles/000005571/mini-pcs.htmlI hope this helps. Wanner G.