Bug 210479

Summary: amdgpu: Monitor connected to RX 6800XT loses signal when module is loaded
Product: Drivers Reporter: alapshin
Component: Video(DRI - non Intel)Assignee: drivers_video-dri
Status: RESOLVED INVALID    
Severity: normal CC: alexdeucher
Priority: P1    
Hardware: All   
OS: Linux   
Kernel Version: 5.10.0-rc6 Subsystem:
Regression: No Bisected commit-id:
Attachments: Journalctl output

Description alapshin 2020-12-03 17:03:32 UTC
Created attachment 293923 [details]
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
Comment 1 Alex Deucher 2020-12-03 18:08:34 UTC
It looks like you don't have support for the display hardware configured in your kernel config.  Make sure your config has:
CONFIG_DRM_AMD_DC=y
CONFIG_DRM_AMD_DC_DCN=y
CONFIG_DRM_AMD_DC_DCN3_0=y
Comment 2 alapshin 2020-12-04 06:21:52 UTC
Alex, thank you very much.

This was exactly it. I had CONFIG_DRM_AMD_DC_DCN3_0 unset. After enabling it everything seems to work fine, including XServer.