bisect result: lp:~ubuntu-kernel/ubuntu/+source/linux/+git/unstable
shows this commit.

I built using the mainline config-4.15.0-041500rc2-generic file and
accepted default options. I also had to apply
ff6fa2d396b0476988c749664f600b1e177bcf9b in order to get the neighboring
commits to build.

it does appear to stop the flicker, but also seems to cause the boot

commit 77a113c1ac1458856ca8e82a9046efff8ca87f09
Author: Andy Whitcroft <>
Date:   Wed Apr 16 19:40:57 2014 +0100

    UBUNTU: SAUCE: vt -- maintain bootloader screen mode and content until vt 
    Introduce a new VT mode KD_TRANSPARENT which endevours to leave the current
    content of the framebuffer untouched.  This allows the bootloader to insert
    a graphical splash and have the kernel maintain it until the OS splash
    can take over.  When we finally switch away (either through programs like
    plymouth or manually) the content is lost and the VT reverts to text mode.
    Signed-off-by: Andy Whitcroft <>

:040000 040000 b0f28f7ecaeaf8037832299ee421886dcd9dfc25 
3e051b4e05da82a1184bdb45a71d3317e8c74445 M      drivers
:040000 040000 22bdb68e3e9757318cf57f010231c1af7db61cc1 
ce199b29dcc261c74b4b2cdfd26dc3993ecbd970 M      include

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  Kernel crash when booting laptop with hdmi monitor connected

Status in linux package in Ubuntu:

Bug description:
  When I boot a Dell Inspiron 7559 with an external monitor connected to
  the hdmi port, it usually shows only a blank screen after grub and I
  have to hard power off the laptop. The issue is present when the bios
  and grub are in mirror mode to both screens. I can see the following
  stack trace in journalctl:

  syslog contains:
   kernel: Missing switch case (6) in intel_prepare_dp_ddi_buffers

  This occurs with both a Dell U2515H using an HDMI cord, and a HP
  Compaq LA2405wg connected via HDMI-to-DVI adapter.

  WORKAROUND: Keep the monitor unplugged until the Ubuntu loading screen
  shows up.

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: linux-image-4.15.0-20-generic 4.15.0-20.21
  ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
  Uname: Linux 4.15.0-20-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7
  Architecture: amd64
  CurrentDesktop: ubuntu:GNOME
  Date: Mon Apr 30 17:22:20 2018
  InstallationDate: Installed on 2018-04-28 (2 days ago)
  InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
  SourcePackage: linux-signed
  UpgradeStatus: No upgrade log present (probably fresh install)

  This is a fresh install. I have modified grub defaults to include 
"acpi_osi=!Windows 2015" But I tested without the acpi_osi parameter and see 
the same issue although the system now randomly crashes later on.
  ApportVersion: 2.20.9-0ubuntu7
  Architecture: amd64
   /dev/snd/controlC0:  apatterson   1965 F.... pulseaudio
  CurrentDesktop: ubuntu:GNOME
  DistroRelease: Ubuntu 18.04
  HibernationDevice: RESUME=UUID=7b947b8e-de50-4ab6-b7f3-254a5dea924a
  InstallationDate: Installed on 2018-04-28 (9 days ago)
  InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
  MachineType: Dell Inc. Inspiron 7559
  Package: linux (not installed)
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.15.0-20-generic 
root=UUID=77f1cfec-1fe4-4201-9a91-9f00a5d7782b ro quiet splash 
"acpi_osi=!Windows 2015"
  ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
   linux-restricted-modules-4.15.0-20-generic N/A
   linux-backports-modules-4.15.0-20-generic  N/A
   linux-firmware                             1.173
  Tags:  bionic wayland-session
  Uname: Linux 4.15.0-20-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dialout dip lpadmin plugdev sambashare sudo wireshark
  _MarkForUpload: True 09/26/2017
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: 1.2.5 0H0CC0
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A00
  dmi.chassis.type: 10
  dmi.chassis.vendor: Dell Inc.
  dmi.chassis.version: Not Specified
dmi:bvnDellInc.:bvr1.2.5:bd09/26/2017:svnDellInc.:pnInspiron7559:pvr1.2.5:rvnDellInc.:rn0H0CC0:rvrA00:cvnDellInc.:ct10:cvrNotSpecified: Inspiron Inspiron 7559
  dmi.product.version: 1.2.5
  dmi.sys.vendor: Dell Inc.

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