Linux ubuntu 5.4.0-1025-raspi introduces cursor lag especially for tablets

[Jonathan Gutow]

By returning my raspberry Pi4 to Linux ubuntu 5.4.0-1022-raspi, I was able to verify that the lag is introduced between that version and Linux ubuntu 5.4.0-1025-raspi. I do not appear to have anything intermediate on my system. I also noted that under Wayland the neither the separate cursor for the tablet or the mouse cursor shows lag in the newer kernel. Unfortunately, I have no other clue as to what is going on.

The system report will show Linux ubuntu 5.4.0-1022-raspi as I have rolled back to that to avoid the problem for now.

ubuntu 20.04.1 LTS

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-1022-raspi 5.4.0-1022.25
ProcVersionSignature: Ubuntu 5.4.0-1022.25-raspi 5.4.65
Uname: Linux 5.4.0-1022-raspi aarch64
ApportVersion: 2.20.11-0ubuntu27.13
Architecture: arm64
CasperMD5CheckResult: skip
CurrentDesktop: LXQt
Date: Sat Dec 12 16:27:02 2020
ImageMediaBuild: 20200731
SourcePackage: linux-raspi
UpgradeStatus: No upgrade log present (probably fresh install)

[Jonathan Gutow (gutow)]

A little more information that may help:

1) Same issue seen with a complete new install of ubuntu-server-20.04 for pi 4 + Lubuntu.
2) If I do not include `dtoverlay=vc4-fkms-v3d` in \boot\firmware\usercfg.txt the lag goes away. However this introduces random screen flashing and other screen update artifacts such as blank regions.

[Juerg Haefliger (juergh)]

Is this still an issue with a fresh install and latest kernel 5.4.0-1032.35?

[Jonathan Gutow (gutow)]

I can verify that the lag is gone in 5.4.0-1032.35. This should be closed.

[Juerg Haefliger (juergh)]

Thanks for the confirmation.