When my Dell XPS 15 9570 laptop is on, the monitors plugged in the HDMI port are correctly detected. Unplugging a monitor also works as expected.

However, when waking up from suspend by briefly lifting the lid open, the HDMI port is not reconfigured. Whatever was plugged at the time it was suspended is still considered connected on resume.

Moreover, the resolution of a previously plugged monitor is kept, causing "not supported resolution" if a monitor with a smaller resolution was plugged before resuming. Re-connecting the new monitor fixes the issue in this case.

I have not figured out exactly how, but leaving the lid open when suspended or after resuming seems to change this behavior.

How can I force the HDMI ports to be scanned again on resume? or otherwise work around this annoying issue.

Some more context:

  • Dual GPU, integrated Intel UHD 630 in use (i915)
  • Discrete nvidia GPU disabled, no proprietary drivers loaded
  • Debian 10 (buster)
  • Linux 4.19.0-2: nouveau.runpm=0 acpi_rev_override=1 acpi_osi=Linux nouveau.modeset=0 scsi_mod.use_blk_mq=1 mem_sleep_default=deep
  • Wayland 1.16, Gnome 3.30
  • /sys/power/mem_sleep: s2idle [deep]
  • I don't have any specific idea to solve the problem, but have you tried running xrandr (no args) just to see whether the port's connected/disconnected/or_what, and maybe get some other useful diagnostic info? – John Forkosh Apr 3 at 9:53
  • @JohnForkosh thanks, I will try but I have little hope that xrandr will have any effect under Wayland. – istepaniuk Apr 3 at 13:29
  • Yeah, I agree "little hope", but maybe just a little >0. The point was that I think when/if you find the answer, it'll turn out that the info you gave us wouldn't have been adequate to find (or even guess) that answer. Oh..., so maybe try running dmesg as root right after "lifting the lid". Maybe there'll be some unexpected diagnostic near the end of the file, or something. That's just another shot in the dark, but I think you'll just have to keep shooting until you hit something useful. – John Forkosh Apr 4 at 6:21
  • @JohnForkosh it did not reveal anything unexpected. For xrandr, after resume, an XWAYLAND output with the old resolution is still "plugged in". After unplugging and plugging the HDMI back, it correctly shows the new resolution. I suspect it's a kernel issue (udev, drm, kms, i915...) or given that swapping monitors while suspended might not be that common, it could even be a BIOS issue. As you suggest, I will keep going down the rabbit hole. I was expecting that this was a common issue. – istepaniuk Apr 5 at 11:33

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