[Bug 95016] New: X unresponsive + faulty image when changing external screen resolution using xrandr

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=95016

            Bug ID: 95016
           Summary: X unresponsive + faulty image when changing external
                    screen resolution using xrandr
           Product: DRI
           Version: XOrg 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: gt6 at gmx.net
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 123046
  --> https://bugs.freedesktop.org/attachment.cgi?id=123046&action=edit
Faulty tiled image in frozen X after running xrandr

Bug description:
This is a Dell XPS 13 9343 (2015) with a native resolution of 1920x1080 via
eDP. If I boot it with an external screen (3440x1440) attached via DP, the
image from the laptop gets mirrored automatically when X starts. If I attempt
to change the resolution and layout by running

xrandr --output DP1 --auto --right-of eDP1
  or
xrandr --output DP1 --mode 3440x1440 --right-of eDP1

then X becomes unresponsive 9 out of 10 times and I have to kill it from
another VT (e.g. TTY2). The resolution of the external screen does indeed
change, but the image from the laptop is tiled a bunch of times and I can't
interact with anything (the mouse cursor is frozen, too).

Attached is a screenshot I managed to grab by running

xrandr --output eDP1 --auto --output DP1 --auto --right-of eDP1 & (sleep 4;
scrot)

In the screenshot, the upper left tile is on my laptop as I expect it. The part
on the right is the external screen showing the unexpected tiling.

The problem exists in drm-intel-nightly


System environment:
-- chipset: Intel Broadwell-U
-- system architecture: 64-bit
-- xf86-video-intel: 1:2.99.917+622+gde44aaa-1
-- xserver: 1.18.3-1
-- mesa: 11.2.0-1
-- libdrm: 2.4.67-2
-- kernel: problem present on 4.4.5-1, 4.5-1 and
linux-drm-intel-nightly-20160419-1
-- Linux distribution: Archlinux
-- Machine or mobo model: Dell XPS 13 9343
-- Display connector: internal eDP, external DP


Reproducing steps:
 * Connect external screen via DP
 * run xrandr --output DP1 --auto --right-of eDP1


Additional info:
Xorg.0.log is attached. The output regarding xrandr (timestamp 3041.823) seems
normal. The "got pause for" output comes from me switching to TTY2 after the
problem occurs.
dmesg with debug is attached.
xrandr --verbose is attached (for the rare case that changing the resolution
worked).

> uname -a
Linux tachychineta 4.6.0-1-drm-intel-nightly #1 SMP PREEMPT Tue Apr 19 12:00:49
CEST 2016 x86_64 GNU/Linux

I wasn't able to create a vbios dump:
> echo 1 > /sys/devices/pci0000:00/0000:00:02.0/rom
> cat /sys/devices/pci0000:00/0000:00:02.0/rom > vbios.dump
cat: '/sys/devices/pci0000:00/0000:00:02.0/rom': Input/output error

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