[Bug 210479] New: amdgpu: Monitor connected to RX 6800XT loses signal when module is loaded

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=210479

            Bug ID: 210479
           Summary: amdgpu: Monitor connected to RX 6800XT loses signal
                    when module is loaded
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.10.0-rc6
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - non Intel)
          Assignee: drivers_video-dri at kernel-bugs.osdl.org
          Reporter: alapshin at fastmail.com
        Regression: No

Created attachment 293923
  --> https://bugzilla.kernel.org/attachment.cgi?id=293923&action=edit
Journalctl output

When monitor is connected to RX 6800XT gpu it loses its signal as soon as
amgdpu module is loaded from initrd.

However system itself is working, I can enter LUKS password and connect via
ssh.
Adding nomodeset kernel parameter allows to see boot progress but Xserver can't
be started and user is redirected to console login prompt.

Additional info
1. This monitor works fine with same setup (hardware/OS) with Nvidia GPU and
modesetting driver.
2. This situation occurs regardless how monitor is connected (DisplayPort or
HDMI)
3. This situation also occurs with different monitor as well.
4. This GPU seems to work fine under Windows installed on same hardware.

lspci -nvv output:

2d:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc.
[AMD/ATI] Device [1002:73bf] (rev c1) (prog-if 00 [VGA controller])
        Subsystem: Advanced Micro Devices, Inc. [AMD/ATI] Device [1002:0e3a]
        Flags: bus master, fast devsel, latency 0, IRQ 43, IOMMU group 2
        Memory at 7800000000 (64-bit, prefetchable) [size=16G]
        Memory at 7c00000000 (64-bit, prefetchable) [size=256M]
        I/O ports at e000 [size=256]
        Memory at fc700000 (32-bit, non-prefetchable) [size=1M]
        Expansion ROM at fc800000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel driver in use: amdgpu
        Kernel modules: amdgpu

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