[Bug 110031] Failure to configure monitors with dc enabled

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110031

            Bug ID: 110031
           Summary: Failure to configure monitors with dc enabled
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: tom at compton.nu

I have a new machine with an RX 570 card and three monitors connected that
works with booting with amdgpu.dc=0 but fails to configure the monitors
correctly under both Wayland and Gnome when display is enabled (the default).

First the basics of the setup - it's an RX 570 with three monitors, left to
right:

  NEC LCD2170NX 1600x1200 rotated 90 degrees and connected to HDMI-A-1
  Dell 3007WFPHC 2560x1600 connected to DVI-1-D
  NEC LCD2170NX 1600x1200 rotated 90 degrees and connected to DP-1

The BIOS initially turns on the left and right monitors but once the kernel
starts booting the DVI connected monitor in the middle is turned on as well
with all three showing he same image.

By default Gnome tries to start gdm under Wayland but all three screens go
blank and the kernel logs a failure to commit the mode change.

Forcing X instead will get the gdm greeter displayed on the right hand screen
only but after logging in it's impossible to activate the middle screen though
the left hand one can be.

If I boot with the left and right screens physically unplugged (not just turned
off) then X will activate the middle monitor and I can then plug the others in
and use them successfully. This does not work with Wayland however.

Booting with display core disabled causes everything to work fine under both
Wayland and X sessions.

Logs (with amdgpu.dc_log=1 drm.debug=6) for both Wayland and X boots are
attached. A summary of some possibly relevant software versions is:

  kernel-4.20.14-200.fc29.x86_64
  libdrm-2.4.97-1.fc29.x86_64
  mesa-dri-drivers-18.3.4-1.fc29.x86_64
  mutter-3.30.2-2.fc29.x86_64
  gnome-shell-3.30.2-1.fc29.x86_64
  xorg-x11-drv-amdgpu-18.1.0-1.fc29.x86_64
  xorg-x11-server-Xorg-1.20.4-1.fc29.x86_64

Hopefully this isn't in completely the wrong place but please do say if you
think it should be somewhere else or if there are other tests I should try etc.

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