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[Bug 1597267] Re: ThinkPad X260 connecting external DisplayPort hangs system


As per the description, I have tested this with 4.4.0-28-generic as well
as mainline 4.6.3-040603-generic and 4.7.0-040700rc5-generic; they all
hang in a similar fashion.

In fact, the journal output I attached was from the 4.7 kernel, I
renamed the attachment accordingly:  ubuntu16-04_linux4.7.0-040700rc5

** Tags added: kernel-bug-exists-upstream

** Changed in: linux (Ubuntu)
       Status: Incomplete => Confirmed

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  ThinkPad X260 connecting external DisplayPort hangs system

Status in linux package in Ubuntu:

Bug description:
  Running Ubuntu 16.04 on a Lenovo ThinkPad X260 with Intel Skylake HD
  Graphics 520, connecting an external monitor to the DisplayPort
  connector causes the system to quickly hang. The system stops
  responding to network pings, cannot switch consoles, and needs a hard

  The external monitor does work when using a text console, and does not
  always hang in the LightDM login screen, but starting up a desktop
  session will always hang.

  This originally happened using a ThinkPad dock, and I tested it
  further using an external DP monitor. This happens on 4.4.0-28-generic
  as well as mainline 4.6.3-040603-generic and 4.7.0-040700rc5-generic;
  they all hang in a similar fashion.

  I have attached a journalctl log from running 4.7.0-040700rc5-generic
  and connecting the DP monitor while in a text console, before
  switching to the graphical console and logging in. The system hangs
  after a series of:

  kernel: WARNING: CPU: 3 PID: 2319 at /home/kernel/COD/linux/drivers/gpu/drm/i915/intel_pm.c:3647 skl_update_other_pipe_wm+0x15d/0x170 [i915]
  kernel: WARNING: CPU: 3 PID: 4418 at /home/kernel/COD/linux/drivers/gpu/drm/i915/intel_display.c:13957 skl_max_scale.part.108+0x69/0x70 [i915]
  kernel: [drm:gen8_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun

  The first warnings come immediately when connecting, and others when
  switching consoles and logging in.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: linux-image-4.4.0-28-generic 4.4.0-28.47
  ProcVersionSignature: Ubuntu 4.4.0-28.47-generic 4.4.13
  Uname: Linux 4.4.0-28-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.1
  Architecture: amd64
   /dev/snd/controlC0:  terom      1903 F.... pulseaudio
  CurrentDesktop: Unity
  Date: Wed Jun 29 13:03:18 2016
  InstallationDate: Installed on 2016-06-26 (2 days ago)
  InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
  MachineType: LENOVO 20F6007RGE
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-28-generic root=UUID=6636a3bb-262e-4ab2-ae81-d9388e3f7684 ro rootflags=subvol=@ quiet splash
   linux-restricted-modules-4.4.0-28-generic N/A
   linux-backports-modules-4.4.0-28-generic  N/A
   linux-firmware                            1.157.1
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 06/01/2016
  dmi.bios.vendor: LENOVO
  dmi.bios.version: R02ET48W (1.21 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 20F6007RGE
  dmi.board.vendor: LENOVO
  dmi.board.version: SDK0J40705 WIN
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: None
  dmi.modalias: dmi:bvnLENOVO:bvrR02ET48W(1.21):bd06/01/2016:svnLENOVO:pn20F6007RGE:pvrThinkPadX260:rvnLENOVO:rn20F6007RGE:rvrSDK0J40705WIN:cvnLENOVO:ct10:cvrNone:
  dmi.product.name: 20F6007RGE
  dmi.product.version: ThinkPad X260
  dmi.sys.vendor: LENOVO

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