Multi-head setup - use only one display for vc

Zucca · Last edited by Zucca on Thu Jan 17, 2019 11:20 am; edited 1 time in total

My google-fu failed.

I know there is a way to disable displays via kernel command line.
I have three different resolution monitors on my desk and on the them is rotated. To look less messy I'd like to disable all but one, until user inside X/wayland -session turns the other(s) on.

I think it was some kms feature...
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xdarma · Posted: Mon Jan 14, 2019 7:19 am Post subject:

Maybe this comment can be useful?
Permanently disable second screen
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Zucca · Posted: Mon Jan 14, 2019 5:20 pm Post subject:

Do you happen to remember how to list all the display connectors from kernel's perspective. I remember that xrandr lists aren't neccessary same.

I guesss I could find them from /sys maybe ... Hmmm.
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Zucca · Posted: Wed Jan 16, 2019 9:47 pm Post subject:

Ok. I tried messing with video= on kernel command line and I lost all the native resolutions of my screens.
I guess the setting must conflict with my amdgpu drivers. Maybe I should try to command amdgpu instead of video?
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Ant P. · Watchman Joined: 18 Apr 2009 Posts: 6920

I'm also interested in the answer to this, but haven't figured it out so far.
(two displays, want fbcon to fill the larger one but still use both for X11. Disabling one on the cmdline seems to permanently remove it until reboot.)

Zucca · Posted: Thu Jan 17, 2019 11:30 am Post subject:

I changed the topic title to fit better and hopefully lure in someone who knows the answer.

In meantime I had an idea: Replace vc with kmscon as early as possible in the boot process. This may need initramfs. I just don't have any idea how to do it. Or if it's even possible. Then add disabling of the other display(s) in the mix...

I'll try to RTFM of kmscon...
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sao98021 · Posted: Thu Jan 17, 2019 11:31 am Post subject:

meh i didn't see that you already messed around with 'video', so scratch that. except i guess the resolution issue, i suppose you could also set it manually with <xres> x <yres>: resolution

it would look like

Zucca · Posted: Thu Jan 17, 2019 12:09 pm Post subject:

Yeah. Using video= messes things up. :(
I actually managed to get it working on vc BUT

other diplays were on until OpenRC configured virtual console
setting resolution via video= (4k in my case) resulted to blank screen, so leaving resolution unspecified gave me a resolution which had thumb sized fonts
after entering X there wasn't any resolution higher than 1024*768 to choose from xfce's display configuration (amdgpu got disabled?)

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sao98021 · Posted: Thu Jan 17, 2019 12:27 pm Post subject:

Zucca · Posted: Thu Jan 17, 2019 5:40 pm Post subject:

I didn't bother to test. Even if the resolution setting would work on lower resolutions, being not able to turn other displays back on is a no-go. And I assume changing resolution on my primary display would not somehow enable turning on other displays later on. So I think disabling diplay outputs via video= is permanent, until reboot.
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