Qubes 4.1 not detecting external monitor over HDMI


so recently I’ve built an 4.1 ISO (23rd March master branch) and succesfully installed on my Zenbook Pro Duo. It mostly works, but I’ve noticed a few issues (perhaps bugs?), that raised an eyebrow.

I’ve had to add to grub nouveau.modeset=0 rd.blacklist.drivers=nouveau as otherwise the LUKS passphrase screen was flickering.

Now, when I actually start the laptop with external monitor plugged via HDMI, the LUKS passphrase screen is displayed on the external monitor. However, after entering valid passphrase the HDMI screen turns black, and the user login screen is displayed on my laptops screen.

Once I’m logged in, when I go to Q → System Tools → Display I can only see the two built-in displays from my laptop. Yes, two. This is the Asus Zenbook Pro Duo - it’s got a secondary 4K screen/tablet above the keyboard.

xrandr in dom0 (1.4 KB)

Now I’m not sure what could be the issue here. I mean I suspect it might be that the HDMI port is connected to nVidia card, but then why would it work on LUKS screen? So I guess it has something to do with X, as it seems to “forget” about that display when X starts.

I’ll greatly appreciate any hints how to debug or fix this.

With love,

So is the laptop not rebooting after login anymore?

I’m guessing grub uses some generic display driver to show you the luks prompt, but then the system loads and there is nothing to drive your nvidia card since you blacklisted nouveau, so you only see whatever your iGPU can see.

Before I blacklisted the nouveau driver I still could log in (its just the LUKS screen looked glitchy) however the HDMI external monitor was also not detected. In fact, blacklisting nouveau “kinda” progressed things, in the sense that:

Before blacklisting:

  • LUKS screen glitchy
  • everything was displayed on laptops builtin monitor
  • HDMI monitor not detected before login
  • HDMI monitor not detected after login

After blacklisting

  • LUKS screen displayed as expected, no glitches
  • before login (LUKS screen) displayed on HDMI monitor
  • after login HDMI monitor not detected

You won’t be able to display anything on the external monitor because nothing is driving the gpu it connects to. You need to either load nouveau or the proprietary driver (discouraged and might be hard/impossible to get working in Qubes)

EDIT: have you tried running other Linuxes on this machine? Are the displays handed properly?

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