I recently purchased a couple 4k monitors for my Thinkpad P51s setup with a dock. I previously used two 1080p monitors with no issues via DisplayPort => HDMI connectors from the dock => monitors.
Now with DisplayPort => DisplayPort connections to the monitors, both are discoverable (and light up during boot), but only one is used by Ubuntu once Ubuntu boots up to the login screen.
They are both discoverable in Ubuntu 20.04, and I can make either primary, but even if I have the second one configured as secondary, only the primary displays.
The only thing that has physically changed is the dock (I have the exact same model, but I left the other one at a different workstation), and the introduction of 4k monitors at 60Hz instead of 1080p monitors at lesser frequency (~30Hz).
How should I go about troubleshooting this?
Some specs:
I was using X.Org X server -- Noveau display driver from xserver-xorg-video-nouveau (open source), but switched to Using NVIDIA driver metapackage from nvidia-driver-470 (proprietary, tested).
sudo lshw -C video
*-display
description: VGA compatible controller
product: HD Graphics 620
vendor: Intel Corporation
physical id: 2
bus info: pci@0000:00:02.0
version: 02
width: 64 bits
clock: 33MHz
capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
configuration: driver=i915 latency=0
resources: irq:135 memory:eb000000-ebffffff memory:80000000-8fffffff ioport:e000(size=64) memory:c0000-dffff
*-display
description: 3D controller
product: GM108GLM [Quadro M520 Mobile]
vendor: NVIDIA Corporation
physical id: 0
bus info: pci@0000:02:00.0
version: a2
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list
configuration: driver=nouveau latency=0
resources: irq:136 memory:ec000000-ecffffff memory:90000000-9fffffff memory:a0000000-a1ffffff ioport:d000(size=128)
xrandr
Screen 0: minimum 320 x 200, current 3840 x 2872, maximum 16384 x 16384
eDP-1 connected (normal left inverted right x axis y axis)
1920x1080 60.01 + 60.01 59.97 59.96 59.93
1680x1050 59.95 59.88
1600x1024 60.17
1400x1050 59.98
1600x900 59.99 59.94 59.95 59.82
1280x1024 60.02
1440x900 59.89
1400x900 59.96 59.88
1280x960 60.00
1440x810 60.00 59.97
1368x768 59.88 59.85
1360x768 59.80 59.96
1280x800 59.99 59.97 59.81 59.91
1152x864 60.00
1280x720 60.00 59.99 59.86 59.74
1024x768 60.04 60.00
960x720 60.00
928x696 60.05
896x672 60.01
1024x576 59.95 59.96 59.90 59.82
960x600 59.93 60.00
960x540 59.96 59.99 59.63 59.82
800x600 60.00 60.32 56.25
840x525 60.01 59.88
864x486 59.92 59.57
800x512 60.17
700x525 59.98
800x450 59.95 59.82
640x512 60.02
720x450 59.89
700x450 59.96 59.88
640x480 60.00 59.94
720x405 59.51 58.99
684x384 59.88 59.85
680x384 59.80 59.96
640x400 59.88 59.98
576x432 60.06
640x360 59.86 59.83 59.84 59.32
512x384 60.00
512x288 60.00 59.92
480x270 59.63 59.82
400x300 60.32 56.34
432x243 59.92 59.57
320x240 60.05
360x202 59.51 59.13
320x180 59.84 59.32
DP-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-2 disconnected (normal left inverted right x axis y axis)
HDMI-2 disconnected (normal left inverted right x axis y axis)
DP-2-1 connected primary 3840x2160+0+712 (normal left inverted right x axis y axis) 597mm x 336mm
3840x2160 60.00*+ 60.00 59.94 30.00 25.00 24.00 29.97 23.98
2560x1440 59.95
2048x1280 59.99
1920x1080 60.00 60.00 50.00 59.94 25.00 24.00 23.98
1600x1200 60.00
1600x900 60.00
1280x1024 75.02 60.02
1152x864 75.00
1280x720 60.00 59.94
1024x768 75.03 60.00
800x600 75.00 60.32
720x576 50.00
720x480 60.00 59.94
640x480 75.00 60.00 59.94
720x400 70.08
DP-2-2 connected (normal left inverted right x axis y axis)
3840x2160 60.00 + 60.00 59.94 30.00 25.00 24.00 29.97 23.98
2560x1440 59.95
2048x1280 59.99
1920x1080 60.00 60.00 50.00 59.94 25.00 24.00 23.98
1600x1200 60.00
1600x900 60.00
1280x1024 75.02 60.02
1152x864 75.00
1280x720 60.00 59.94
1024x768 75.03 60.00
800x600 75.00 60.32
720x576 50.00
720x480 60.00 59.94
640x480 75.00 60.00 59.94
720x400 70.08
DP-2-3 disconnected (normal left inverted right x axis y axis)
