[Bug 105150] New: i915 HDMI + DP output cannot work at the same time

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105150

            Bug ID: 105150
           Summary: i915 HDMI + DP output cannot work at the same time
           Product: DRI
           Version: DRI git
          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: freedesktop at delyan.me
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 137421
  --> https://bugs.freedesktop.org/attachment.cgi?id=137421&action=edit
archive with dmesg log and video of the issue

Steps to reproduce:

1. Attach monitor via DP. 
2. Observe normal detection and proper display.
3. Attach second monitor via HDMI.
4. Observe normal detection and corrupted image across all displays (DP, HDMI
and eDP builtin panel)
5. Unplug HDMI cable.
6. Observe image restored to DP output and eDP builtin panel.

This also reproduces if HDMI is first (works fine) and DP is second (image
across all displays gets corrupted again). In other words, one is fine, both
together result in corruption.

Repro is off of commit bc46f2468bfb7a9ca16d28bdcc3fc7cd2cc628b8 (drm-tip).

Attached is dmesg from the issue with `drm.debug=0xe log_buf_len=1M`.

Attached is also a video of the issue, reproduced using two inputs to the same
4k monitor (Acer S277HK), using picture-in-picture mode (large image is DP, PIP
is HDMI). I figured the pattern is too regular, you may actually recognize it
:) 

I can also successfully reproduce this on two separate Dell UP3017 monitors,
using either a WD-15 Thunderbolt dock or direct connection to the laptop.

I believe this used to work around 4.10 but due to an update of the OS (Ubuntu
17.04 -> 17.10), I am no longer able to go back that far unless I build my own
kernel.

Platform: Dell Precision 7510
GPU: Iris Pro Graphics P580 (rev 09) (part of a Xeon E3-1545M v5 package)

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