[Bug 107393] 4.18.0-rc6 amdgpu framebuffer problems with DisplayPort

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107393

            Bug ID: 107393
           Summary: 4.18.0-rc6 amdgpu framebuffer problems with
                    DisplayPort
           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: lkd-fdo at sky-haven.net

Created attachment 140848
  --> https://bugs.freedesktop.org/attachment.cgi?id=140848&action=edit
combined kernel dmesg for two boot sessions, one in 4.17.0 and the other in
4.18.0-rc6

On kernel 4.17.0, amdgpudrmfb functions correctly; taking the fb from efifb

On kernel 4.18.0-rc6 (and previous), the framebuffer proper doesn't start;
monitor doesn't get a valid display signal. If I log in and blind-start a
Wayland compositor (sway in my case), the display gets a desktop and things
work normally. Once I exit out back to FB, the display is blanked.

Everything works normally if I connect the monitor with HDMI instead.

This was a problem with 4.18.0-rc5 as well. I was pointed to the patch at
https://lists.freedesktop.org/archives/amd-gfx/2018-July/023920.html and
applied it to 4.18.0-rc5, but it had no effect on behavior.

GPU: Vega64
Monitor: Acer XR341CK

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