I'm running Ubuntu 20.04 on a Dell XPS 15 9570. I've been happily using external monitors on it with minimal issues until today, where it's suddenly started to shut off the external display after a few minutes, and only recognises it again if I unplug the cable (running over USBC-HDMI)
Some digging earlier made me suspect this error from the syslog was possibly related:
kernel: [ 3012.555110] [drm:intel_dp_link_training_clock_recovery [i915]] *ERROR* failed to get link status
However the only info I could find on this suggested it had been fixed in later kernel versions so it was a bit of a dead end!
How can I go about diagnosing what the cause of the issue actually is, assuming nobody can guess at the cause from this admittedly brief description!
EDIT A bit more context from /var/log/syslog
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.774697] pcieport 0000:00:1b.0: pciehp: Slot(20): Link Down
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.774699] pcieport 0000:00:1b.0: pciehp: Slot(20): Card not present
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.774725] pcieport 0000:02:00.0: Refused to change power state, currently in D3
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.775195] pcieport 0000:03:02.0: Refused to change power state, currently in D3
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.775283] xhci_hcd 0000:3a:00.0: Refused to change power state, currently in D3
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853014] xhci_hcd 0000:3a:00.0: Refused to change power state, currently in D3
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853038] xhci_hcd 0000:3a:00.0: Controller not ready at resume -19
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853039] xhci_hcd 0000:3a:00.0: PCI post-resume error -19!
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853042] xhci_hcd 0000:3a:00.0: HC died; cleaning up
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853055] xhci_hcd 0000:3a:00.0: remove, state 4
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853058] usb usb4: USB disconnect, device number 1
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853286] xhci_hcd 0000:3a:00.0: USB bus 4 deregistered
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853293] xhci_hcd 0000:3a:00.0: remove, state 4
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853295] usb usb3: USB disconnect, device number 1
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853503] xhci_hcd 0000:3a:00.0: Host halt failed, -19
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853509] xhci_hcd 0000:3a:00.0: Host not accessible, reset failed.
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853592] xhci_hcd 0000:3a:00.0: USB bus 3 deregistered
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853809] pcieport 0000:03:01.0: Refused to change power state, currently in D3
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.853989] pcieport 0000:03:00.0: Refused to change power state, currently in D3
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.854817] pci_bus 0000:04: busn_res: [bus 04] is released
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.854896] pci_bus 0000:05: busn_res: [bus 05-39] is released
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.855085] pci_bus 0000:3a: busn_res: [bus 3a] is released
Nov 13 17:10:56 linlapuk007 kernel: [ 3051.855142] pci_bus 0000:03: busn_res: [bus 03-3a] is released
