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System:

  • Kubuntu 20.10 on Linux 5.8.0-48
  • HP Pavilion 15-EC1073DX

Graphics info:  AMD RX Vega 6 (Ryzen 4600H) is connected to the laptop display. I want to use only the laptop display by default, and always be able to switch back to it if needed. Nvidia GTX 1650 Mobile is connected to the laptop display (possibly through the AMD graphics) and to the HDMI port. I want to keep this off to save power, except when using a display connected via the HDMI port.

I can use either graphics on the laptop display, but I have to restart my system (probably just Xorg, but that's still a pain) to apply any changes. When using the integrated AMD graphics alone, my computer works nicely, except it can't even detect any display plugged into the HDMI port. When using the Nvidia graphics, everything works nicely, but the power consumption is substantially higher, according to my research. When using Nvidia Prime in on-demand mode, my computer successfully detects an HDMI screen, but doesn't give any output to it when I configure my system to use it.

How do I keep the Nvidia card off, or at least idle, by default, but also be able to (quickly) start using the Nvidia card to drive the HDMI display?

To be clear, I don't want this to interfere with any running GUI applications, and I'd prefer mirroring the laptop display to the HDMI display, but combining the two displays next to each other into a single Xorg session, or using them with separate Xorg sessions, would also be okay.

Progress update:  I've sort of made it work using separate Xorg instances with different config files, but it's messy. When I start Xorg from the display manager (sddm), or from a terminal without specifying a config file, everything works nicely. But when I specify any config file with xinit -- -config, even the default /etc/X11/xorg.conf, xinit doesn't show anything, and repeatedly outputs "No protocol specified" to the terminal. I can work around this by running Xorg directly with a specified config file, and then ~/.xinitrc with the DISPLAY environment variable set properly. So something about specifying an Xorg config file messes up xinit (and startx).

Objective update:  I underestimated the difficulty of doing things on just the HDMI display, so I'd really like to have some way to show the same screen to both displays at the same time.

Progress update #2:  multiple Xorg sessions don't seem to work very well together, at least with KDE Plasma 5.19.5, so that option is probably off the table.

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  • related: unix.stackexchange.com/questions/578666/… . I just hope nvidia proprietary driver plays nicely with these settings today...
    – A.B
    Apr 7, 2021 at 7:19
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    Also it's not clear from the description if your system is "muxless" or not (maybe it can do both kinds). I'd be curious about the laptop brand/model.
    – A.B
    Apr 7, 2021 at 7:28
  • @A.B I tried the method you referenced, but it didn't give any output to the HDMI display. Also, the laptop is an HP Pavilion 15-EC1073DX. Apr 8, 2021 at 4:03

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