[radeon] Static effect on HDMI out using kernel 5.11 and later (but 5.8.0-50-generic works)

[magowiz]

lsb_release -rd
Description: Ubuntu 21.04
Release: 21.04

package version : kernel-image 5.11.0-16-generic

what I expect to happen : to show my desktop correctly on second hdmi monitor
what happens : static effect like shown in attached photo

Since upgrade to hirsute (21.04) from groovy (20.10) my hdmi port on my graphic card stopped to work correctly and started to display static effect on second monitor, as you can see from the attached photo.

Here it is mine videocards:
Code:

$ lspci | grep VGA
01:05.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RS880M [Mobility Radeon HD 4225/4250]
02:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Park [Mobility Radeon HD 5430/5450/5470]

I was able to test it with 3 different kernels :
Code:

5.12.1-051201-generic # last mainline kernel
5.11.0-16-generic # last official kernel from hirsute
5.8.0-50-generic # probably a old kernel still there from groovy

Only the older one, 5.8.0-50-generic was working correctly with dual monitor with no issues.

Kind regards

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: xorg 1:7.7+22ubuntu1
ProcVersionSignature: Ubuntu 5.11.0-16.17-generic 5.11.12
Uname: Linux 5.11.0-16-generic x86_64
.tmp.unity_support_test.0:

ApportVersion: 2.20.11-0ubuntu65
Architecture: amd64
BootLog: Error: [Errno 13] Permesso negato: '/var/log/boot.log'
CasperMD5CheckResult: unknown
CompizPlugins: [core,bailer,detection,composite,opengl,compiztoolbox,decor,move,gnomecompat,vpswitch,place,grid,regex,session,snap,mousepoll,imgpng,resize,wall,animation,unitymtgrabhandles,expo,ezoom,fade,workarounds,scale,unityshell]
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Sat May 8 18:45:37 2021
DistUpgraded: 2021-04-22 22:22:18,672 ERROR got error from PostInstallScript ./xorg_fix_proprietary.py (g-io-error-quark: Failed to execute child process “./xorg_fix_proprietary.py”: Failed to execve: File o directory non esistente (1))
DistroCodename: hirsute
DistroVariant: ubuntu
DkmsStatus:
 virtualbox, 6.1.18, 5.11.0-16-generic, x86_64: installed
 virtualbox, 6.1.18, 5.8.0-50-generic, x86_64: installed
ExtraDebuggingInterest: Yes
GraphicsCard:
 Advanced Micro Devices, Inc. [AMD/ATI] RS880M [Mobility Radeon HD 4225/4250] [1002:9712] (prog-if 00 [VGA controller])
   Subsystem: Hewlett-Packard Company RS880M [Mobility Radeon HD 4225/4250] [103c:1441]
 Advanced Micro Devices, Inc. [AMD/ATI] Park [Mobility Radeon HD 5430/5450/5470] [1002:68e0] (prog-if 00 [VGA controller])
   Subsystem: Hewlett-Packard Company Park [Mobility Radeon HD 5430/5450/5470] [103c:1441]
InstallationDate: Installed on 2019-10-26 (560 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
MachineType: Hewlett-Packard HP Pavilion dv6 Notebook PC
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.11.0-16-generic root=UUID=a5324660-5421-487c-ad0f-b562bd39c622 ro quiet splash vt.handoff=7
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to hirsute on 2021-04-22 (15 days ago)
dmi.bios.date: 02/25/2013
dmi.bios.release: 15.41
dmi.bios.vendor: Hewlett-Packard
dmi.bios.version: F.29
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: 1441
dmi.board.vendor: Hewlett-Packard
dmi.board.version: 67.33
dmi.chassis.type: 10
dmi.chassis.vendor: Hewlett-Packard
dmi.chassis.version: N/A
dmi.ec.firmware.release: 103.51
dmi.modalias: dmi:bvnHewlett-Packard:bvrF.29:bd02/25/2013:br15.41:efr103.51:svnHewlett-Packard:pnHPPaviliondv6NotebookPC:pvr059C110000243010000020100:rvnHewlett-Packard:rn1441:rvr67.33:cvnHewlett-Packard:ct10:cvrN/A:
dmi.product.family: 103C_5335KV
dmi.product.name: HP Pavilion dv6 Notebook PC
dmi.product.sku: XD610EA#ABZ
dmi.product.version: 059C110000243010000020100
dmi.sys.vendor: Hewlett-Packard
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.104-1build1
version.libgl1-mesa-dri: libgl1-mesa-dri 21.0.1-2
version.libgl1-mesa-glx: libgl1-mesa-glx N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.20.11-1ubuntu1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:19.1.0-2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20200714-1ubuntu1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.17-1

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This change was made by a bot.

[magowiz (magowiz)]

Kernel version 5.11.0-18 fixed this issue, should I mark it resolved/fixed?