Blank screen (Cannot find any crtc or sizes) since Kernel 4.17 (AMDGPU.DC) on Amd Radeon RX460 on HDMI LG Ultrawidescreen Monitor

Submitted by Naheem Zaffar

Assigned to Default DRI bug account

Description

Created attachment 141265
Dmesg from boot with Kernel 4.19 prerelease

I have already reported this on Redhat Bugzilla, so if more information is needed, that may be a good place to look at comments: https://bugzilla.redhat.com/show_bug.cgi?id=1594488

Since the change to using dc in the kernel I am getting a blank screen with trying to boot my ultrawidescreen monitor.

As a workaround I can use amdgpu.dc=0, but this hits al earlier big where at native resolution the display output is garbled (links in Redhat Bugzilla attach to another big report, youtube video of the same).

I am attaching dmesg output from 4.19.0-0.rc0.git8.1.vanilla.knurd.1.fc28.x86_64 with and without amdgpu.dc=0

I have noticed a couple of entries in the dmesg without the amdgpu.dc=0:

kernel: [drm] add ip block number 4 <dm>

with amdgpu.dc=0 it is:

kernel: [drm] add ip block number 4 <dce_v11_0>

The other ip address block entries are identical.

with amdgpu.dc=0 I get this section:

Aug 22 23:46:22 kernel: [drm] PCIE GART of 256M enabled (table at 0x000000F400900000).
Aug 22 23:46:22 kernel: [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
Aug 22 23:46:22 kernel: [drm] Driver supports precise vblank timestamp query.
Aug 22 23:46:22 kernel: [drm] AMDGPU Display Connectors
Aug 22 23:46:22 kernel: [drm] Connector 0:
Aug 22 23:46:22 kernel: [drm] DP-1
Aug 22 23:46:22 kernel: [drm] HPD5
Aug 22 23:46:22 kernel: [drm] DDC: 0x4868 0x4868 0x4869 0x4869 0x486a 0x486a 0x486b 0x486b
Aug 22 23:46:22 kernel: [drm] Encoders:
Aug 22 23:46:22 kernel: [drm] DFP1: INTERNAL_UNIPHY1
Aug 22 23:46:22 kernel: [drm] Connector 1:
Aug 22 23:46:22 kernel: [drm] HDMI-A-1
Aug 22 23:46:22 kernel: [drm] HPD3
Aug 22 23:46:22 kernel: [drm] DDC: 0x4874 0x4874 0x4875 0x4875 0x4876 0x4876 0x4877 0x4877
Aug 22 23:46:22 kernel: [drm] Encoders:
Aug 22 23:46:22 kernel: [drm] DFP2: INTERNAL_UNIPHY1
Aug 22 23:46:22 kernel: [drm] Connector 2:
Aug 22 23:46:22 kernel: [drm] DVI-D-1
Aug 22 23:46:22 kernel: [drm] HPD4
Aug 22 23:46:22 kernel: [drm] DDC: 0x4878 0x4878 0x4879 0x4879 0x487a 0x487a 0x487b 0x487b
Aug 22 23:46:22 kernel: [drm] Encoders:
Aug 22 23:46:22 kernel: [drm] DFP3: INTERNAL_UNIPHY
Aug 22 23:46:22 kernel: [drm] Chained IB support enabled!

but without amdgpu.dc=0 only the first and last line of that section appear.

Later down without the amdgpu.dc=0 I also get the following message:

kernel: [drm] Cannot find any crtc or sizes

This may also be similar to bug https://bugs.freedesktop.org/show_bug.cgi?id=105880 but that is for laptop panels on LVDS while this issue is with a discrete RX460 graphics card on HDMI

Attachment 141265, "Dmesg from boot with Kernel 4.19 prerelease":
dmesg-4.19.log