ASUS ROG PG278Q Monitor not detected using DisplayPort over USB-C on Intel NUC8i5BEK with Kernel 5.3.1

djzin · 10-02-2019, 01:22 AM

I have just installed a new linux system to an Intel NUC8i5BEK. Over HDMI everything works perfectly, but using my monitor (which only has DisplayPort input) it seems it is not detected properly. The UEFI BIOS correctly detects the monitor and puts it at native resolution, but when KMS kicks in the kernel switches back to 1024x768.

Weirdly the framebuffer resolution is kept at the native resolution (2560x1440), so text scrolls off the screen unless I reset the framebuffer

This problem occurs with the default Arch Linux ISO (ARCH_201909), but also with my custom-compiled kernel 5.3.1 for which I have debugging info.

The most confusing thing trying to debug this is why there are TWO DisplayPort outputs on the graphics card as reported by the kernel (there is only 1 DisplayPort on the rear of the device that I can see). One of them lists some resolutions but the highest is 1024x768; this seems to be the one it is using.

Here is the kernel drm log with all debugging enabled:
https://pastebin.com/VNhZGJPu

Here is my kernel config:
https://pastebin.com/hStMFVfE

I can "fix" this by e.g. disabling modesetting in the kernel command line, but it is not ideal because for instance I cannot then turn the monitor off while the computer is on; I also cannot hotplug monitors.

Any help appreciated!

mrmazda · 10-02-2019, 06:49 PM

Quote:

Originally Posted by djzin

The most confusing thing trying to debug this is why there are TWO DisplayPort outputs on the graphics card as reported by the kernel (there is only 1 DisplayPort on the rear of the device that I can see).

X (kernel?) routinely reports more logical outputs than physical outputs, especially with Intel GPUs. With MST, one physical output port can drive bunches of physical displays.

Does your monitor menu have an option to switch among different DP versions?

djzin · 10-03-2019, 12:46 AM

Quote:

Originally Posted by mrmazda

X (kernel?) routinely reports more logical outputs than physical outputs, especially with Intel GPUs. With MST, one physical output port can drive bunches of physical displays.

Does your monitor menu have an option to switch among different DP versions?

Must be the kernel as I don't have an X server running.
There is no option to change DP mode on the monitor (not very many options on the monitor at all).

Here's what the kernel reports:

Code:

bash-5.0$ ls /sys/class/drm
card0  card0-DP-1  card0-DP-2  card0-HDMI-A-1  renderD128  version

Code:

bash-5.0$ for port in card0-*; do echo $port; cat $port/enabled $port/modes; done
card0-DP-1
disabled
card0-DP-2
enabled
1024x768
800x600
800x600
848x480
640x480
card0-HDMI-A-1
disabled

mrmazda · 10-03-2019, 07:15 AM

Whether this might help you I have no idea:

Code:

# ls /sys/class/drm
card0
card0-DP-1
card0-DP-2
card0-HDMI-A-1
card0-HDMI-A-2
card0-HDMI-A-3
renderD128
version
# xrandr --listproviders
Providers: number : 1
Provider 0: id: 0x47; cap: 0xf (Source Output, Sink Output, Source Offload, Sink Offload); crtcs: 3; outputs: 5; associated providers: 0; name: modesetting
    output DP-1
    output HDMI-1
    output HDMI-2
    output HDMI-3
    output DP-2
# xrandr | egrep 'onnect|creen|\*' | sort -r
Screen 0: minimum 320 x 200, current 5120 x 1440, maximum 8192 x 8192
HDMI-3 disconnected (normal left inverted right x axis y axis)
HDMI-2 connected 2560x1080+2560+0 (normal left inverted right x axis y axis) 673mm x 284mm
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
DP-1 connected primary 2560x1440+0+0 (normal left inverted right x axis y axis) 598mm x 336mm
   2560x1440     59.95*+  74.92
   2560x1080     60.00*+
# inxi -V | head -n1
inxi 3.0.36-00 (2019-08-14)
# inxi -GxxSMza
System:    Host: ab250 Kernel: 5.2.14-1-default x86_64 bits: 64 compiler: gcc v: 9.2.1
           parameters: BOOT_IMAGE=/boot/vmlinuz root=/dev/sdableep noresume ipv6.disable=1 net.ifnames=0
           mitigations=auto consoleblank=0 video=1024x768@60 video=1400x900@60 3 drm.debug=0x1e log_buf_len=1M
           Desktop: IceWM 1.5.4 dm: startx Distro: openSUSE Tumbleweed 20190927
Machine:   Type: Desktop Mobo: ASUSTeK model: PRIME B250M-C v: Rev X.0x serial: <filter> UEFI: American Megatrends
           v: 1402 date: 11/16/2018
Graphics:  Device-1: Intel HD Graphics 630 vendor: ASUSTeK driver: i915 v: kernel bus ID: 00:02.0 chip ID: 8086:5912
           Display: server: X.Org 1.20.5 driver: modesetting unloaded: fbdev,vesa alternate: intel
           resolution: 2560x1440~60Hz, 2560x1080~60Hz
           OpenGL: renderer: Mesa DRI Intel HD Graphics 630 (Kaby Lake GT2) v: 4.5 Mesa 19.1.7 compat-v: 3.0
           direct render: Yes