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I always work with an external monitor, which wasn't a problem since a couple of weeks ago. Since then most of the time (not everytime!) the external screen is not recognized.

Tldr; What always seems to work is disconnecting the dongle, cold boot into windows, connect the dongle, hot reboot into ubuntu.

Long read with what I have tried:

The specs:

  • Asus Zenbook UX391U
  • Intel graphics 620
  • Ubuntu 19.10
  • The usb c -> hdmi dongle that came with the laptop
  • Dual boot ubuntu / windows configuration

What I've tried that did not work:

  • The zenbook only has three usb c connectors. I've tried all of them, only once did one of them work while switching the connector while booted
  • Four different monitors
  • Used a whole lot of hdmi cables
  • Tried three different usb c dongles
  • Updating the drivers in Windows (since it's officially a windows laptop, and the support for it is for windows).
  • Reinstalling Windows and Ubuntu.
  • RMA'ing it to ASUS. They could not duplicate my issues.

So, that last one is weird. Asus could not duplicate the issue... My problems don't seem entirely random: - Connecting it to my screen at home for the first time in a long time did work. Afterwards not anymore. - One of the usb c connectors seemed to work a lot, before I Rma'd it to Asus.

What always seems to work is disconnecting the dongle, cold boot into windows, connect the dongle, hot reboot into ubuntu. So to me seems as some kinda driver issue in Ubuntu? Some config gets messed up?

When reverting the procedure (cold boot ubuntu, hot boot into windows) I hardly every have an external screen, Windows does however recognized something connected and says that the 'screen functionality might be limited' and something about me having to check the displayport connection (translated from Dutch).

wout
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1 Answers1

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Sounds like a kernel problem, the kernel is the home of intel driver (or some other driver related to the problem, it's all in the kernel). Since you have tried three different usb-c adaptors and since at least one of them used to work until recently, a kernel bug is my guess. I have run into one of these myself recently, but a different problem.

This means you may need to report a kernel bug. To be helpful, you'll be invited to try different kernels to isolate when the bug hit.

The first thing would be to see if going back to an old kernel helps. One of the problems is that if your problem has been introduced by a change in a driver, that change may have backported to all the current kernels supported by Ubuntu 19.10. So even though the Advanced login when you start Ubuntu gives you the choice of 'old' kernels, they may still have the problem, particularly if the problem was introduced by a security patch, since security patches are backported with alacrity.

You can grab kernels from this 'library': https://wiki.ubuntu.com/Kernel/MainlineBuilds

Or you can make a previous version of an Ubuntu kernel. Compiling kernels is much easier than it used to be, and it's fun. Use the git method. see this: https://wiki.ubuntu.com/KernelTeam/GitKernelBuild but it misses one or two steps, my notes here (a key missing step is rm vmlinux-gdb.py https://askubuntu.com/a/1190174/152287)

It takes a while (30 minutes or so, depending on your hardware, and allow 60 GB during the build). The git download will have all the versions like a time-machine, so you can 'bisect' to see where the problem began. You have to learn the basics of git (git tag, git checkout and optionally git bisect).

Once you have found when the problem was introduced, see https://wiki.ubuntu.com/Kernel/FAQ

Tim Richardson
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  • Thanks for the quick reply. I will have to schedule some time to dive into installing different kernels, and allow for some time to be sure the problem is fixed (since the problem seems to be not entirely binary). – wout Dec 16 '19 at 11:40