I have a problem with my dual monitor setup on an AMD RX 580: when I lock the screen and Gnome try to power off both monitors the following happens:
1) the second monitor goes to sleep before the first one, this is normal and expected because the first monitor has a longer time to sleep
2) after some seconds the second monitor turn on back again and prevents the first one to sleep at all
3) gnome detects inactivity on the lock screen for some time and try to power off the monitors again
4) step 1 all over again in an infinite loop
When I login back from the lock screen the windows inside my Gnome session can sometimes be rearranged from one screen to the other.
After discovering this behavior I tried to power off the monitors manually with `xset dpms force off` and I can confirm that the same happens: the monitors wont really power off because the second one turns back on and prevents the first one to sleep.
My guess was that somehow when the second monitor was turning off it delivered some kind of "monitors changed, you should reset" message to the GPU which in order did some kind of "reset everything and power on the monitors back again" action.
Searching for a fix to this problem I tried to upgrade my amdgpu mesa drivers using the oibaf/graphics-drivers ppa and after this I tried to upgrade my whole distribution too, moving from bionic to cosmic.
Nothing worked.
In the end I discovered the existence of amdgpu.dc and tried to disable it with `GRUB_CMDLINE_LINUX_DEFAULT="amdgpu.dc=0"`, this did the trick but it is still a workaround.
I'm not sure this is the right place to report this kind of issues but as the issue is somehow critical (the first I entered the power on/off loop I didn't notice it and my monitor cycled power for two hours) I hope this will help other people.
---
ProblemType: Bug
AlsaVersion: Advanced Linux Sound Architecture Driver Version k4.17.0-9-generic.
ApportVersion: 2.20.10-0ubuntu9
Architecture: amd64
Card0.Amixer.info:
Card hw:0 'PCH'/'HDA Intel PCH at 0xf7f10000 irq 30'
Mixer name : 'Realtek ALC892'
Components : 'HDA:10ec0892,104385b0,00100302'
Controls : 50
Simple ctrls : 22
Card1.Amixer.info:
Card hw:1 'HDMI'/'HDA ATI HDMI at 0xf7e60000 irq 31'
Mixer name : 'ATI R6xx HDMI'
Components : 'HDA:1002aa01,00aa0100,00100700'
Controls : 42
Simple ctrls : 6
CurrentDesktop: GNOME
DistroRelease: Ubuntu 18.10
HibernationDevice: RESUME=UUID=7cd1c323-140b-4412-a67a-c46d90a91ff2
InstallationDate: Installed on 2018-09-01 (3 days ago)
InstallationMedia: Ubuntu-Server 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
MachineType: ASUS All Series
Package: linux (not installed)
ProcFB: 0 amdgpudrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.17.0-9-generic root=UUID=edb6f869-3d1b-4726-bbf1-44b736abfe2b ro amdgpu.dc=0
ProcVersionSignature: Ubuntu 4.17.0-9.10-generic 4.17.17
RelatedPackageVersions:
linux-restricted-modules-4.17.0-9-generic N/A
linux-backports-modules-4.17.0-9-generic N/A
linux-firmware 1.174
RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
Tags: cosmic
Uname: Linux 4.17.0-9-generic x86_64
UpgradeStatus: Upgraded to cosmic on 2018-09-04 (0 days ago)
UserGroups: adm audio cdrom dip lpadmin lxd plugdev sambashare sudo vboxusers
_MarkForUpload: True
dmi.bios.date: 08/15/2014
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 2103
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: Z87-C
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2103:bd08/15/2014:svnASUS:pnAllSeries:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnZ87-C:rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.family: ASUS MB
dmi.product.name: All Series
dmi.product.version: System Version
dmi.sys.vendor: ASUS
This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:
apport-collect 1790861
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the Ubuntu Kernel Team.