[Bug 107546] New: Screen is frozen on second connection of DP MST dock

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107546

            Bug ID: 107546
           Summary: Screen is frozen on second connection of DP MST dock
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: sergey.menshikov at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Kernel 4.15.0.30 Ubuntu 18.04.1 Xorg/Gnome Lenovo 4th gen X1 20FBxxx Skylake i7
Intel built-in video, Lenovo OneLink+ DP MST dock with dual dell 24" displays

Error messages upon dock disconnect:

[drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable link training
[drm:intel_mst_pre_enable_dp [i915]] *ERROR* failed to allocate vcpi

Next connection leads to frozen screen on laptop, no change on exterenal
monitors. 

[drm:intel_wait_ddi_buf_idle [i915]] *ERROR* Timeout waiting for DDI BUF C idle
bit

Disconnecting the dock restores laptop screen functionality, but subsequent
connection of the dock has the same symptoms repeating. Reboot fixes the issue
until first dock disconnect. 

My workaround is to enable GuC firmware loading and boot without the dock
attached.

sudo vi /etc/modprobe.d/i915.conf

options i915 enable_guc_loading=1 enable_guc_submission=1

sudo update-initramfs -u
sudo reboot

(reboot while not connected to dock)

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