[Bug 98516] New: [i915][SNB] black screen in X when resuming from suspend or hibernate

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98516

            Bug ID: 98516
           Summary: [i915][SNB] black screen in X when resuming from
                    suspend or hibernate
           Product: DRI
           Version: unspecified
          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: freedesktop at equaeghe.nospammail.net
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 127639
  --> https://bugs.freedesktop.org/attachment.cgi?id=127639&action=edit
dmesg output after issue occurred

# System Information

Linux <hostname> 4.8.5-gentoo #1 SMP <datetime> 2016 x86_64 Intel(R) Core(TM)
i7-2620M CPU @ 2.70GHz GenuineIntel GNU/Linux

Manufacturer: LENOVO
Product Name: 4290W4H
Version: ThinkPad X220

Internal connector: LVDS
Connection to external displays: often DP (via docking station), sometimes VGA
(directly)

# Problem description

Often, but not always (about half of the time, say), when resuming from suspend
(to RAM) or hibernate (to disk), I get a black screen instead of the lock
screen (X 1.18.4, SDDM 0.13.0, KWin 5.7.5). The mouse cursor is visible and can
be moved and often I get a brief flash of the lock screen (or desktop?) before
the screen turns black. Such brief flashes also sometimes occur when switching
to a VT. VTs do work.

My impression is that it happens more often after I've disconnected from the DP
display, if not upon the first sleep thereafter, then a subsequent one (without
intermediate reboot).

I used to be able to reliably resume in the past, but since I upgraded from
KDE4 to KDE5, many i915-related issues appeared. I'd read that this was known.
After a number of updates both to KDE and the kernel version, many issues went
away. This issue is the only remaining major one.

# Some information gathered

When switching to the console, a kernel message sometimes appears:

kernel: [drm:intel_dp_link_training_clock_recovery [i915]] *ERROR* failed to
enable link training
kernel: [drm:intel_dp_start_link_train [i915]] *ERROR* failed to start channel
equalization

I started following the guide at
https://01.org/linuxgraphics/documentation/how-report-bugs, so enabled the
drm.debug=0x1e log_buf_len=1M options. I attach a resulting dmesg output; my
impression is that due to the options, my dmesg is ‘filled’ with stuff that may
not be relevant.

Also important to note is that since I activated the kernel options, I've had a
different type of issue, which I think essentially locked my computer. The X
screen had also turned black and drm-related messages appeared on a VT console
I could change to (only one change was possible, I think, before thinks locked
up even further).

# Request

I realize that I haven't followed all instructions at
https://01.org/linuxgraphics/documentation/how-report-bugs, but I hope the
information I provided is enough to get feedback on how to diagnose further.

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