[Bug 93578] New: Intel HD 520 failed to train DP when connected with a external monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93578

            Bug ID: 93578
           Summary: Intel HD 520 failed to train DP when connected with a
                    external monitor
           Product: DRI
           Version: DRI 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: mariolpantunes at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 120796
  --> https://bugs.freedesktop.org/attachment.cgi?id=120796&action=edit
dmesg log when I start the system with a external monitor connected.

Dear all, I have a dell XPS 13 9350, with a external bus DA200. This adapter
connects to the USB-C port and provides HDMI, VGA, 1x USB 3 and Ethernet. The
usb port and the Ethernet are working correctly. However I am unable to connect
a external monitor.

I am using Slackware64-current with the latest 4.4 kernel (rc8).
The dmesg log points to drm intel drivers as the culprit:

[    4.526617]  [<ffffffffc02d3c4a>] skl_update_other_pipe_wm+0x1ba/0x1c0
[i915]
[    4.526628]  [<ffffffffc02d3e81>] skl_update_wm+0x231/0x720 [i915]
[    4.526642]  [<ffffffffc02d82ee>] intel_update_watermarks+0x1e/0x30 [i915]
[    4.526660]  [<ffffffffc033ed28>] haswell_crtc_enable+0x378/0x860 [i915]
[    4.526677]  [<ffffffffc033a9f5>] intel_atomic_commit+0x475/0x13c0 [i915]
[    4.526702]  [<ffffffffc0351bde>] intel_fbdev_output_poll_changed+0x1e/0x30
[i915]
[    4.671697] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU
pipe B FIFO underrun
[    5.072287] [drm:intel_dp_link_training_channel_equalization [i915]] *ERROR*
failed to train DP, aborting
[    5.488287] [drm:intel_dp_link_training_channel_equalization [i915]] *ERROR*
failed to train DP, aborting
[    5.904336] [drm:intel_dp_link_training_channel_equalization [i915]] *ERROR*
failed to train DP, aborting

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