[Bug 1873895] Re: Regression: block staircase display with side-by-side monitors of different pixel widths

Mathew Hodson 1873895 at bugs.launchpad.net
Sun Apr 18 07:13:07 UTC 2021

** No longer affects: libxcb (Ubuntu)

** No longer affects: libxcb (Ubuntu Focal)

** No longer affects: libxcb (Ubuntu Groovy)

** Changed in: xserver-xorg-video-amdgpu (Ubuntu)
       Status: Incomplete => Triaged

** Changed in: xserver-xorg-video-amdgpu (Ubuntu Focal)
       Status: Incomplete => Triaged

** Changed in: xserver-xorg-video-amdgpu (Ubuntu Groovy)
       Status: Incomplete => Triaged

** Changed in: xserver-xorg-video-amdgpu (Ubuntu Focal)
   Importance: Undecided => High

** Changed in: xserver-xorg-video-amdgpu (Ubuntu Groovy)
   Importance: Undecided => High

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  Regression: block staircase display with side-by-side monitors of
  different pixel widths

Status in xf86-video-amd:
Status in xfwm4 package in Ubuntu:
  Fix Released
Status in xserver-xorg-video-amdgpu package in Ubuntu:
Status in xfwm4 source package in Focal:
  In Progress
Status in xserver-xorg-video-amdgpu source package in Focal:
Status in xfwm4 source package in Groovy:
  Fix Released
Status in xserver-xorg-video-amdgpu source package in Groovy:

Bug description:

   * This issue affects AMD graphics on Xfwm4 4.14.1.

   * Windows are displayed staggered with a multi-window layout

  [Test Plan]

   * Use AMD graphics drivers

   * Connect a second display at a different resolution

   * Open multiple windows

   * While the issue is present, the windows and desktop will appeared

   * Once fixed, they display normally.

  [Where problems could occur]

   * Regression potential should be relatively low, as the release
  between 4.14.1 and 4.14.5 are bug releases.

   * With window managers, some changes could lead to different behavior
  and other broken displays. Non-AMD graphics users should also test for

  [Other Info]
   * Please see the Xfwm4 release notes for changes between 4.14.1 and 4.14.5: https://gitlab.xfce.org/xfce/xfwm4/-/blob/xfce-4.14/NEWS#L7-44

  [Original Report]

  Update based on further research.

  This only happens when the secondary external display is operating at
  a different pixel width to the internal. In this case eDP is 1920x1080
  whereas the external HDMI-A-0 is natively 1680x1050.

  It is caused by xfwm4's recent switch from using glx to xpresent for

  The underlying bug is in the AMD driver.

  I was able to reproduce on an external 1920x1200 display only when it
  was set to a non-native 1680x1050 resolution.

  Two identical Lenovo E495 laptops with 20.04 installed. The problem occurred initially on the laptop that is having package upgrades applied regularly.

  With dual monitors and the external monitor placed left or right the
  display has a blocked staircase effect shown in the attached
  photograph, and seems related to


  More detailed investigation suggests it only happens when the X
  coordinate of the two monitors is different. The symptom looks like an
  off-by-one error because it appears as if the display is divided into,
  say, 10 rows and 15 columns but the first row has 16 'columns' worth
  of blocks on it and so wraps to the beginning of the 2nd row, and so

  On the laptop without package upgrades being applied this didn't
  happen. So I upgraded it (314 packages) and restarted and it too sees
  the same problem.

  I suspected libxcomposite1 and downgraded it to 1:0.4.5-0ubuntu1 but
  that didn't solve it.

  I now suspect libxcb but so far haven't been able to prove it.
  ProblemType: Bug
  ApportVersion: 2.20.11-0ubuntu27
  Architecture: amd64
  BootLog: Error: [Errno 13] Permission denied: '/var/log/boot.log'
  CasperMD5CheckResult: skip
  CompositorRunning: None
  CurrentDesktop: XFCE
  DistUpgraded: Fresh install
  DistroCodename: focal
  DistroRelease: Ubuntu 20.04
  DistroVariant: ubuntu
   Advanced Micro Devices, Inc. [AMD/ATI] Picasso [1002:15d8] (rev c1) (prog-if 00 [VGA controller])
     Subsystem: Lenovo ThinkPad E595 [17aa:5124]
  InstallationDate: Installed on 2020-04-08 (11 days ago)
  InstallationMedia: Xubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200408)
  MachineType: LENOVO 20NECTO1WW
  Package: xserver-xorg-video-amdgpu 19.1.0-1
  PackageArchitecture: amd64
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.4.0-21-generic root=/dev/mapper/ELLOE000-rootfs ro acpi_osi=! "acpi_osi=Windows 2016" quiet splash vt.handoff=7
  ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
  Tags:  focal ubuntu ubuntu
  Uname: Linux 5.4.0-21-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip libvirt lp lpadmin lxd plugdev sambashare sudo users
  _MarkForUpload: True
  dmi.bios.date: 12/23/2019
  dmi.bios.vendor: LENOVO
  dmi.bios.version: R11ET32W (1.12 )
  dmi.board.asset.tag: Not Available
  dmi.board.name: 20NECTO1WW
  dmi.board.vendor: LENOVO
  dmi.board.version: Not Defined
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: None
  dmi.modalias: dmi:bvnLENOVO:bvrR11ET32W(1.12):bd12/23/2019:svnLENOVO:pn20NECTO1WW:pvrThinkPadE495:rvnLENOVO:rn20NECTO1WW:rvrNotDefined:cvnLENOVO:ct10:cvrNone:
  dmi.product.family: ThinkPad E495
  dmi.product.name: 20NECTO1WW
  dmi.product.sku: LENOVO_MT_20NE_BU_Think_FM_ThinkPad E495
  dmi.product.version: ThinkPad E495
  dmi.sys.vendor: LENOVO
  version.compiz: compiz N/A
  version.libdrm2: libdrm2 2.4.101-2
  version.libgl1-mesa-dri: libgl1-mesa-dri 20.0.4-2ubuntu1
  version.libgl1-mesa-glx: libgl1-mesa-glx N/A
  version.xserver-xorg-core: xserver-xorg-core 2:1.20.8-2ubuntu2
  version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
  version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.1.0-1
  version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20200226-1
  version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.16-1

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