Affects me as well. Reproduced on:

* Dell XPS 7390, i7-10510U, integrated graphics, laptop screen
* Focal with latest updates
* Kernels:
  * 5.8.0-55-generic (linux-image-generic-hwe-20.04)
  * 5.13.0-rc4 (vanilla from mainline-ppa)

In the kernel log, "fb0: switching to inteldrmfb from EFI VGA" is the
last line I see before the mode change, and "clocksource: tsc: mask:
0xffffffffffffffff..." is the first line once the screen turns back on.

i915.fastboot=1 is set in kernel cmdline, didn't make any difference.
Resolution is visually the same before and after the mode change.

[    1.202214] fb0: switching to inteldrmfb from EFI VGA
[    1.204981] Console: switching to colour dummy device 80x25
[    1.205002] i915 0000:00:02.0: vgaarb: deactivate vga console
[    1.257470] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[    1.257523] i915 0000:00:02.0: vgaarb: changed VGA decodes: 
olddecodes=io+mem,decodes=io+mem:owns=io+mem
[    1.258039] i915 0000:00:02.0: [drm] Finished loading DMC firmware 
i915/kbl_dmc_ver1_04.bin (v1.4)
[    1.266513] i915 0000:00:02.0: [drm] Panel advertises DPCD backlight 
support, but VBT disagrees. If your backlight controls don't work try booting 
with i915.enable_dpcd_backlight=1. If your machine needs this, please file a 
_new_ bug report on drm/i915, see 
https://gitlab.freedesktop.org/drm/intel/-/wikis/How-to-file-i915-bugs for 
details.
[    1.278853] [drm] Initialized i915 1.6.0 20200515 for 0000:00:02.0 on minor 0
[    1.388057] usb 1-9: new high-speed USB device number 2 using xhci_hcd
[    1.528528] usb 4-1: new SuperSpeed Gen 1 USB device number 2 using xhci_hcd
[    1.543379] usb 1-9: New USB device found, idVendor=2109, idProduct=2812, 
bcdDevice= d.a0
[    1.543392] usb 1-9: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[    1.543399] usb 1-9: Product: USB2.0 Hub             
[    1.543404] usb 1-9: Manufacturer: VIA Labs, Inc.         
[    1.544575] hub 1-9:1.0: USB hub found
[    1.545569] hub 1-9:1.0: 4 ports detected
[    1.564060] tsc: Refined TSC clocksource calibration: 2303.993 MHz
[    1.564082] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 
0x2135f10e1ea, max_idle_ns: 440795202126 ns

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https://bugs.launchpad.net/bugs/1836858

Title:
  Display flickers (monitor loses signal briefly) during "flickerfree"
  boot, while showing the BIOS logo on a black background

Status in Plymouth:
  Unknown
Status in linux package in Ubuntu:
  Confirmed
Status in plymouth package in Ubuntu:
  Confirmed

Bug description:
  I am trying flickerfree boot in 19.10 [1], but find it actually
  flickers part way through:

    1. BIOS logo on a black background.
    2. Display mode resets, no image on a black background briefly.
    3. BIOS logo on a black background.

  The flicker occurs seemingly during kernel startup since my
  peripherals are lit up before the problem occurs.

  Suspecting this might be related to FB handover:

    [    2.751028] fb0: switching to inteldrmfb from EFI VGA

  I tried disabling that with a big hammer:

    i915.modeset=0

  so it stays in efifb, and that works -- no more flickering, providing
  I don't let i915 take over the framebuffer.

  [1] https://discourse.ubuntu.com/t/testing-flickerfree-boot/11854

  ProblemType: Bug
  DistroRelease: Ubuntu 19.10
  Package: linux-image-5.2.0-8-generic 5.2.0-8.9
  ProcVersionSignature: Ubuntu 5.2.0-8.9-generic 5.2.0
  Uname: Linux 5.2.0-8-generic x86_64
  ApportVersion: 2.20.11-0ubuntu5
  Architecture: amd64
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', 
'/dev/snd/controlC0', '/dev/snd/hwC0D2', '/dev/snd/hwC0D0', 
'/dev/snd/pcmC0D9p', '/dev/snd/pcmC0D8p', '/dev/snd/pcmC0D7p', 
'/dev/snd/pcmC0D3p', '/dev/snd/pcmC0D2c', '/dev/snd/pcmC0D0c', 
'/dev/snd/pcmC0D0p', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  Date: Wed Jul 17 16:34:36 2019
  InstallationDate: Installed on 2019-05-02 (76 days ago)
  InstallationMedia: Ubuntu 19.10 "Eoan EANIMAL" - Alpha amd64 (20190501)
  MachineType: LENOVO 10M7CTO1WW
  ProcFB: 0 i915drmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.2.0-8-generic 
root=UUID=9bfb5f01-bdd4-4854-bfce-1c28e2f2f3bc ro quiet splash i915.fastboot=1 
vt.handoff=7
  PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No 
PulseAudio daemon running, or not running as session daemon.
  RelatedPackageVersions:
   linux-restricted-modules-5.2.0-8-generic N/A
   linux-backports-modules-5.2.0-8-generic  N/A
   linux-firmware                           1.180
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 02/06/2018
  dmi.bios.vendor: LENOVO
  dmi.bios.version: M16KT47A
  dmi.board.name: 3102
  dmi.board.vendor: LENOVO
  dmi.board.version: SDK0J40709 WIN 3259627060530
  dmi.chassis.type: 3
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: None
  dmi.modalias: 
dmi:bvnLENOVO:bvrM16KT47A:bd02/06/2018:svnLENOVO:pn10M7CTO1WW:pvrThinkCentreM710s:rvnLENOVO:rn3102:rvrSDK0J40709WIN3259627060530:cvnLENOVO:ct3:cvrNone:
  dmi.product.family: ThinkCentre M710s
  dmi.product.name: 10M7CTO1WW
  dmi.product.sku: LENOVO_MT_10M7_BU_Think_FM_ThinkCentre M710s
  dmi.product.version: ThinkCentre M710s
  dmi.sys.vendor: LENOVO

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