[Bug 109384] Bad DisplayPort enumeration and wrong refresh rate with Hawaii chip

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109384

            Bug ID: 109384
           Summary: Bad DisplayPort enumeration and wrong refresh rate
                    with Hawaii chip
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: fabio0x at keemail.me

Created attachment 143150
  --> https://bugs.freedesktop.org/attachment.cgi?id=143150&action=edit
Xorg.0 log with DC off

I'm running Solus KDE with kernel 4.20.2 but I've had these issues since kernel
4.19. Here's the list of issues with AMDGPU DC enabled:
- With Solus' default kernel flags I have wrong DisplayPort enumeration,
meaning that I get DisplayPort-1 when I turn on the computer, and then
DisplayPort-2 when I get my monitor to sleep and then I wake it up.
- If I put my computer on sleep (suspension) and then wake it up, I cannot set
a usable refresh rate. This means I actually get 40 Hz when I set 60, and 45 Hz
when I set 74 (yeah, I have a bit of screen "overclocking". That's how I found
DisplayPort enumeration is wrong).
- I get microstuttering, particularly noticeable when I drag windows around.

Now, all these issues are non existant if I set the amdgpu.dc=0 kernel flag.
Also, DisplayPort number is DisplayPort-0 under any circumstances.

❯ inxi -G
Graphics:  Device-1: AMD Hawaii PRO [Radeon R9 290/390] driver: amdgpu v:
kernel 
           Display: x11 server: X.Org 1.20.3 driver: amdgpu,ati unloaded:
fbdev,modesetting,vesa 
           resolution: 1920x1080~60Hz 
           OpenGL: 
           renderer: AMD Radeon R9 200 Series (HAWAII DRM 3.27.0
4.20.2-107.current LLVM 7.0.0) 
           v: 4.5 Mesa 18.3.1

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