Can you bisect?

(In reply to Alex Deucher from comment #1)
> Can you bisect?

I am not a developer, just a user. All I can tell you is that the problem arises when upgrading Ubuntu from 19.04 to 19.10.

from your dmesg output:
[    1.094054] [drm:amdgpu_init [amdgpu]] *ERROR* VGACON disables amdgpu kernel modesetting.
Did you enable vga console?

Can you get the dmesg output from when the driver is loaded?

Created attachment 145957 [details]
dmesg output

Do any of the display connectors work properly?  If so which?

I am using the DVI port for my monitor. I can't test the VGA port on the motherboard because I don't have a VGA cable, and my monitor is old and doesn't have an HDMI port. Sorry.

Hi, 

I'm the Peter D. who raised the Ubuntu bug report - writing from a different email address.  I can probably bisect the kernel with a little gentle instruction. 

Initial results are;
Raven ridge APU, VGA port, slow monitor (75Hz max refresh rate),
booting with nomodeset gives a stable display, but a very odd result from xrandr. 

psd@EE:~$ xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080
default connected 1920x1080+0+0 0mm x 0mm
   1920x1080     77.00* 
psd@EE:~$ 

Booting new kernels (5.3 onwards?) and no "nomodeset" gives either a blank screen or a very unstable screen with lots of pixelation and a high risk of going black.  Here is something that I captured earlier: 

psd@EE:~$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 16384 x 16384
DisplayPort-0 disconnected primary (normal left inverted right x axis y axis)
HDMI-A-0 disconnected (normal left inverted right x axis y axis)
DisplayPort-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 531mm x 298mm
   1920x1080     60.00*+
   1680x1050     60.00
   1280x1024     60.02
   1440x900      59.89
   1280x800      59.81
   1152x864      75.00
   1280x720      60.00
   1024x768      70.07    60.00
   800x600       60.32    56.25
   640x480       66.67    59.94
   720x400       70.08
psd@EE:~$ 

"DisplayPort-1" is actually a VGA port.  I believe that there is a conversion chop on the motherboard, an ASROCK B450 Pro4. 

Give me some time to swap hardware again.

All three ports work.  

If my computer boots to a blank screen, plugging in a second monitor "resets" the video and both screens display the desktop as clones.  

There are two monitors; a slow one with a maximum vertical refresh rate of 75 Hz, and a fast one with a maximum vertical refresh rate of 144 Hz.  The fast monitor has DP, HDMI and VGA ports.  The slow monitor has VGA and DVI ports.  The motherboard has DP, HDMI, and VGA ports.  Currently there are cables that can reach ... 
MoBo DP fast monitor
Mobo HDMI (passive adapter) DVI slow monitor
Mobo VGA slow monitor
This can be rearranged if need be.

The reset trick has happened with; 
the slow monitor plugged into the VGA port and being revived when the fast monitor was plugged into the DP, and with 
the fast monitor plugged into the DP and being revived when the slow monitor was plugged into the HDMI port.

Currently using a mainline kernel downloaded from Ubuntu. 

psd@EE:~$ uname -a
Linux EE 5.4.0-050400rc7-generic #201911102031 SMP Mon Nov 11 01:34:23 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
psd@EE:~$

maybe try drm-tip mainline build to see if it's any better?

(In reply to Alex Deucher from comment #3)
> [    1.094054] [drm:amdgpu_init [amdgpu]] *ERROR* VGACON disables amdgpu
> kernel modesetting.
> Did you enable vga console?

FWIW, that message is due to "nomodeset" on the kernel command line, which was presumably used to work around this problem?

Does disabling the iommu help?  Append iommu=off or iommu=pt to the kernel command line.

-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been closed from further activity.

You can subscribe and participate further through the new bug through this link to our GitLab instance: https://gitlab.freedesktop.org/drm/amd/issues/956.