[Bug 110782] New: [drm/i915] Displayport connected screen reports Signal Error after update to 5.1 kernel

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110782

            Bug ID: 110782
           Summary: [drm/i915] Displayport connected screen reports Signal
                    Error after update to 5.1 kernel
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: Blubberbub at protonmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

I'm on Arch Linux and when the Linux kernel was updated from v5.0.13-arch1 to
v5.1.2-arch1 my secondary screen started to report a "Signal Error". (So no
image on the screen at all. Just a little box from the screen itself)
The screen is connected through a thunderbolt docking station, but it was
working fine before the update (and during git bisect) so i assume this is a
regression.

Switching to the -lts kernel line fixed the issue as well, but that's not a
permanent solution, i guess.

-- system architecture: x86_64
-- kernel version: v5.1.2-arch1 
-- Linux distribution: Arch Linux
-- Machine or mother board model: lenovo Thinkpad T480s with a "ThinkPad Pro
Docking Station"
-- Display connector: DP

I did a few steps of git bisect which leads me to believe the problem appeared
in the drm/i915 module:

$ git bisect log
git bisect start
# good: [6ee2c3f93d50b2a9aa7bee32bf16b924f2d98596] Arch Linux kernel
v5.0.13-arch1
git bisect good 6ee2c3f93d50b2a9aa7bee32bf16b924f2d98596
# bad: [8ec0a2cba38f896ebae3c05518c1fc9463db6c0c] Arch Linux kernel
v5.1.2-arch1
git bisect bad 8ec0a2cba38f896ebae3c05518c1fc9463db6c0c
# good: [1c163f4c7b3f621efff9b28a47abb36f7378d783] Linux 5.0
git bisect good 1c163f4c7b3f621efff9b28a47abb36f7378d783
# good: [b5dd0c658c31b469ccff1b637e5124851e7a4a1c] Merge branch 'akpm' (patches
from Andrew)
git bisect good b5dd0c658c31b469ccff1b637e5124851e7a4a1c
# bad: [cf0240a755b8b3df51b0b857b03309a666611d58] Merge tag 'pinctrl-v5.1-1' of
git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl
git bisect bad cf0240a755b8b3df51b0b857b03309a666611d58
# bad: [80201fe175cbf7f3e372f53eba0a881a702ad926] Merge tag
'for-5.1/block-20190302' of git://git.kernel.dk/linux-block
git bisect bad 80201fe175cbf7f3e372f53eba0a881a702ad926
# bad: [5ea3998d56346975c2701df18fb5b6e3ab5c8d9e] Merge tag
'drm-intel-next-2019-02-07' of git://anongit.freedesktop.org/drm/drm-intel into
drm-next
git bisect bad 5ea3998d56346975c2701df18fb5b6e3ab5c8d9e
# bad: [968bf969b47df2481022b9a05eaab02948eec088] drm/i915: Fix skl srckey mask
bits
git bisect bad 968bf969b47df2481022b9a05eaab02948eec088
# good: [25f9cebd7a52ddf15405d74fb5fd4c374f301983] drm/i915: Show all active
engines on hangcheck
git bisect good 25f9cebd7a52ddf15405d74fb5fd4c374f301983
# good: [f42fb2317ffcbd005eeb22b1e49020821a11e23a] Merge drm/drm-next into
drm-intel-next-queued
git bisect good f42fb2317ffcbd005eeb22b1e49020821a11e23a

$ lspci -vnn | grep VGA -A 10 
00:02.0 VGA compatible controller [0300]: Intel Corporation UHD Graphics 620
[8086:5917] (rev 07) (prog-if 00 [VGA controller])
        Subsystem: Lenovo UHD Graphics 620 [17aa:2258]
        Flags: bus master, fast devsel, latency 0, IRQ 157
        Memory at f1000000 (64-bit, non-prefetchable) [size=16M]
        Memory at e0000000 (64-bit, prefetchable) [size=256M]
        I/O ports at e000 [size=64]
        [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel driver in use: i915
        Kernel modules: i915

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