[Bug 109246] HDMI connected monitors fail to sleep and instead turn back on when amdgpu.dc=1

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109246

            Bug ID: 109246
           Summary: HDMI connected monitors fail to sleep and instead turn
                    back on when amdgpu.dc=1
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: t00m4nyerr0rs at gmail.com

Original launchpad thread:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1790861

  Overview:
When my computer tries to suspend my monitors after a period of idleness,
they'll suspend for a few seconds before waking back up.

  Steps to Reproduce:
1) Have a monitor attached over HDMI.
2) Set screen energy saving (in Plasma 5) to 1 minute.
3) After 1 minute has passed, the monitor will try to enter sleep mode. It will
fail and turn back on.
4) The monitor will continue to attempt to enter sleep mode every minute until
interrupted by the user.

  Actual Results:
The monitors turn back on a few seconds after entering sleep mode.

  Expected Results:
The monitors stay in sleep mode.

  Additional Information:
While I have two monitors, this issue is only triggered when one is connected
using HDMI. Connecting only one monitor using HDMI will trigger the problem.
Connecting either one using DVI does not trigger the problem. 
I am unable to test if DisplayPort triggers the problem, as I have no
compatible monitors.
Setting the kernel parameter amdgpu.dc=0 does not cause the problem to trigger.

I haven't confirmed if the other affected users in the launchpad thread are
using HDMI, so I'm only reporting my experience.

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