[Bug 99908] New: [i915] driver crashes with dual 4k monitors on Intel HD 520

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99908

            Bug ID: 99908
           Summary: [i915] driver crashes with dual 4k monitors on Intel
                    HD 520
           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: phil at phord.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 129834
  --> https://bugs.freedesktop.org/attachment.cgi?id=129834&action=edit
xrandr --verbose

Bug description:

My laptop locks up hard (Alt-SysRq-B does not work) when I enable video modes
3840x2160 on both monitors and desktop is extended, not mirrored. If I use
3840x2160 on one monitor and 1920x1080 on the other, it seems stable.  When I
tried 2560x1440 on the 2nd monitor (the native resolution of my built-in laptop
display) it also locked up.

It locked up when I tried to use only one external monitor in 4k mode with my
laptop screen in native resolution (2560x1440), but I did not experiment with
that mode much, so I don't have as much specific information about it.

The crash is very reliable and immediate.

I tried some 4.10 kernel flavors, but I failed when trying to install drm-tip
for testing with latest code.


System environment:
-- chipset: Intel(R) Core(TM) i7-6600U CPU @ 2.60GHz
-- system architecture: 64-bit
-- xf86-video-intel:
-- xserver: xorg-server 2:1.18.4-1ubuntu6
-- mesa: 
-- libdrm: 2.4.70-1
-- kernel: 4.8.0-37-generic
-- Linux distribution: Ubuntu 16.10
-- Machine or mobo model: Lenovo Carbon X1
-- Display connector: HDMI on OnePort dock

Reproducing steps:

Enable extended desktop on two monitors in 3840x2160 resolution. 

Additional info:

$ uname -m ; uname -r
x86_64
4.8.0-37-generic

Lenovo Thinkpad Carbon X1
    description: Notebook
    product: 20FB005LUS (LENOVO_MT_20FB_BU_Think_FM_ThinkPad X1 Carbon 4th)
    vendor: LENOVO
    version: ThinkPad X1 Carbon 4th
    width: 64 bits
    capabilities: smbios-2.8 dmi-2.8 smp vsyscall32
       description: Motherboard
       product: 20FB005LUS
       vendor: LENOVO
       physical id: 0
       version: SDK0J40697 WIN

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