[Bug 109829] New: No image via KVM switch. USB-C->dual DisplayPort->KVM

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109829

            Bug ID: 109829
           Summary: No image via KVM switch. USB-C->dual DisplayPort->KVM
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: stuart at eightfivelabs.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 143523
  --> https://bugs.freedesktop.org/attachment.cgi?id=143523&action=edit
dmesg

Hi all,

I have a NUC7i7BNH with the latest BIOS (0062) running Ubuntu 18.04 (uname -r =
4.18.0-15-generic). I have the NUC connected via USB-C to a dual DisplayPort
adapter, to an Avocent SV340D KVM. Also tried kernel v5.0-rc7.

If I have the KVM on the switch for the NUC, everything works great. If I
switch the KVM to another channel, and then switch back to the NUC, I only get
black screens. The only solution is to hard reboot the NUC.

This relates to a bug I raised on
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1816269.

Specifically [  135.089830] [drm:intel_cpu_fifo_underrun_irq_handler [i915]]
*ERROR* CPU pipe A FIFO underrun followed by a lot of thunderblot hotplug
messages.

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