Broken Nvidia Prime on Lenovo Z70-80 (Nvidia 840m)

[Manvydas]

I’m trying to revive a slightly old Lenovo Z70-80. I haven’t used it for a month or so. Then, I downloaded all the latest updates a couple of weeks ago and something broke. The screen looks as if it's tearing many times per second and some of the middle pixels are repeated on the edge of the screen. I've never seen it behave like that.

I've had problems with Prime on this machine many times before, so I followed the usual steps: ensuing that nouveau is blacklisted, rebuilding the modules, using a custom xorg config, trying out multiple different driver versions, etc. Nothing helped. I even tried a complete re-install of Ubuntu, however, that didn’t help (everything was fine during the install).

I still had an older kernel installed on my machine (5.11.0-16), I booted into it, built all the modules, etc (it started with Intel only, I believe). After a reboot back into 5.11.0-16, the Nvidia drivers started working perfectly. No matter which version. They're still broken in 5.11.0-25 and the kernel is the only difference.

I've mentioned this on Nvidia forums already, but my post didn't get any attention there. It contains a few more details, like the Nvidia debug capture and a video of the craziness on my screen: https://forums.developer.nvidia.com/t/severely-distorted-image-on-a-laptop-with-ubuntu-21-04-nvidia-840m-470-57-02-and-older-drivers/185117

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: linux-image-5.11.0-25-generic 5.11.0-25.27
ProcVersionSignature: Ubuntu 5.11.0-25.27-generic 5.11.22
Uname: Linux 5.11.0-25-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu65.1
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: manvydas 1414 F.... pulseaudio
 /dev/snd/controlC0: manvydas 1414 F.... pulseaudio
CasperMD5CheckResult: pass
Date: Wed Aug 4 20:11:57 2021
InstallationDate: Installed on 2021-07-27 (7 days ago)
InstallationMedia: Ubuntu 21.04 "Hirsute Hippo" - Release amd64 (20210420)
MachineType: LENOVO 80FG
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.11.0-25-generic root=UUID=363daad8-ef8a-44a7-a6b3-a879007f38d8 ro quiet splash 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-5.11.0-25-generic N/A
 linux-backports-modules-5.11.0-25-generic N/A
 linux-firmware 1.197.2
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 09/22/2015
dmi.bios.release: 1.96
dmi.bios.vendor: LENOVO
dmi.bios.version: ABCN96WW
dmi.board.asset.tag: NO Asset Tag
dmi.board.name: Lenovo Z70-80
dmi.board.vendor: LENOVO
dmi.board.version: NO DPK
dmi.chassis.asset.tag: NO Asset Tag
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Lenovo Z70-80
dmi.ec.firmware.release: 1.96
dmi.modalias: dmi:bvnLENOVO:bvrABCN96WW:bd09/22/2015:br1.96:efr1.96:svnLENOVO:pn80FG:pvrLenovoZ70-80:rvnLENOVO:rnLenovoZ70-80:rvrNODPK:cvnLENOVO:ct10:cvrLenovoZ70-80:
dmi.product.family: IDEAPAD
dmi.product.name: 80FG
dmi.product.sku: LENOVO_MT_80FG_BU_idea_FM_Lenovo Z70-80
dmi.product.version: Lenovo Z70-80
dmi.sys.vendor: LENOVO