I have Ubuntu 18.04 on a pure-intel Thinkpad T480. It is usually connected to a couple of external monitors. If I choose suspend from the power icon (holding down alt), the laptop initiates the suspend process,and the two external monitors go into suspend mode. The LED on the laptop starts the blinking cycle to indicate suspend. But a second later, the laptop LED goes back to ON. The display don't start again, but as soon as move the wireless mouse, the external displays turn on. So it does not enter suspend.
- it only does this sometimes, hopefully there is some logging somewhere
- I have since learnt that gnome uses the systemd suspend/resume features, documented here: https://www.freedesktop.org/software/systemd/man/systemd-suspend.service.html
Most of the time it works. I think I will have to watch this and try to find some logging when it doesn't work
Update: journalctl | grep suspend:
pci_pm_suspend(): hcd_pci_suspend+0x0/0x30 returns -16 Jun 17 16:57:46 moncrief kernel: dpm_run_callback(): pci_pm_suspend+0x0/0x150 returns -16 Jun 17 16:57:46 moncrief kernel: PM: Device 0000:00:14.0 failed to suspend async: error -16 Jun 17 16:57:46 moncrief kernel: PM: Some devices failed to suspend, or early wake event detected
courtesy of lspci, the device is
00:14.0 USB controller: Intel Corporation Sunrise Point-LP USB 3.0 xHCI Controller (rev 21)