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I am trying to make a portable Workflow that involves a portable, modular set up. It involves a portable ASUS screen (MB16AC) and a Intel NUC (nuc8v5pnk1) with Ubuntu 20.04 installed.

The setup should be simple, plug in the screen to the NUC using a USB-A to USB-C cable. The screen gets power and the data to show from the NUC through that cable. You should just be able to power up the NUC, the screen will work and take you into the log in screen and after loggin in you are off to the races. However, this is not how it works.

If you turn on the set up what you get is the error that says "Your Device does not support DP alt mode" and does not display the info from the NUC. Now I know the NUC is working and at the login in screen because when I change the screen to a desktop screen, it displays fine. I see the login screen, I login and can do whatever. Interestingly, when i plug in the portable ASUS screen, after this, it shows the data from the NUC just fine. The reason being is that i downloaded and installed a driver for the screen to Ubuntu and when loaded the driver, Ubuntu and the screen work well together. Thats the catch the screen needs the driver to display, but the driver is not available until after login. In the field, I will have only one screen and I need to be able to use the portable ASUS to login. Does anyone know how i can load this driver before login or as part of start up or something similar? I need to fix this issue and i am all set. Any info about this would be appreciated. thank you for your time.

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  • Let me clarify, are you saying that once you log in, this USB type C screen works over type C to type A cable with type A on NUC's side? According to my knowledge that shouldn't be possible, alternate modes are available only through USB type C.
    – gronostaj
    Commented Aug 18, 2020 at 16:37
  • To clarify, the screen is USB-C to USB-C, however, it comes with a USB-C to USB-A adapter and says it should work with the drivers installed. So, we have a male-to-male USB-C cable...one side is plugged into the screen and the other is plugged into the USB-C female side of the adapter, which is then plugged in to the USB-A port on the NUC. We need to use the USB-A port because the USB-C port is occupied by our eGPU.
    – Alan Shteyman
    Commented Aug 19, 2020 at 15:29
  • Interesting. How does Linux detect this screen? Are you getting acceleration from the eGPU on that screen? Would it get detected as something else if connected directly to USB type C? I wonder if the included adapter is maybe something more than just an adapter, like a USB GPU. That would work around the lack of support for alt modes with USB type A.
    – gronostaj
    Commented Aug 19, 2020 at 19:50

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"Your Device does not support DP alt mode" and does not display the info from the NUC.

So with the ASUS screen, the Ubuntu driver does not switch the USB-C conntroller to alternate mode, because it doesn't properly detect it.

Now I know the NUC is working and at the login in screen because when I change the screen to a desktop screen, it displays fine. [...] Interestingly, when i plug in the portable ASUS screen, after this, it shows the data from the NUC just fine.

So, assuming the "Desktop screen" is also using DP over USB-C in Alt-mode, the Ubuntu driver detects it, switches the USB-C to alternate mode, and that persists when you plugin the ASUS screen.

If that is correct, that means one of the drivers involved has a bug, since detection doesn't work for the ASUS. File a bug report with whoever developed the driver you downloaded; they might provide instructions how to get more information from the driver to debug this.

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