VGA Troubles With KVM Switches

IMG_20130313_132650I have never had troubles with activating and deactivating the VGA output on my (old) notebook, an HP 2510p. It has an Intel GM965 VGA controller. I used the VGA output very often because giving presentations is part of my job 😉

Typically, I type something like this:

`xrandr --output VGA1 --auto --right-of LVDS1`

Although it wouldn’t be necessary because KDE automatically detects a newly connected hardware and opens the display configuration dialog. I am simply used to do this on the command line.

With my new notebook — an HP 2570p — this suddenly does not work under some specific circumstances. It has an Intel Corporation 3rd Gen Core processor Graphics Controller which is a processor built-in controller. This specific type is also known as the Ivybridge Mobile GT2.

At a first sight everything looks fine. It immediately detects a monitor or a beamer in the same way as the old notebook did. But it fails in most cases (as far as I could test it yet) as soon as there is a KVM switch in between. It behaves as if nothing is connected and xrandr shows “VGA1 disconnected“.

I run Debian Wheezy with the Linux 3.2.35-amd64 kernel on both notebooks and both use the same i915 kernel module for the graphics hardware. I searched a lot in the Internet but didn’t find any useful hints just some vague discussions and speculations.

Some say that it is related to the kernel driver and/or something with EDID.1 Unfortunately, I could not find out yet what the problem really is. At first I would assume that this actually is a hardware issue of the notebook itself. But this would mean that it cannot be fixed unless it is BIOS-related. Thus, I tend to prefer that it is a software issue 😉 although it is difficult to believe because it seems that exactly the same software and drivers are in use on both notebooks. I compiled the latest Linux kernels 3.4.35 and 3.8.2 but both behaved in the same unsatisfying way.

I will try to debug this further, hence, stay tuned. So what to do now? In the Internet you will find suggestions to manually add mode lines with xrandr. This did not work in my case. It just lead to weird behavior of X11 and/or the built-in display which may be some evidence that it is indeed a software bug or software misbehavior.

I could not find a way to simply force the VGA output up. It seems to be an area of research within the Linux kernel (I will search the kernel code for this 😉

For now I found a quick solution which works! Although I found no way to force the VGA output on during run time there is an option for the Linux kernel to force VGA up. Great success! 😀

Add the following parameter to your kernel command line:2


After that the VGA output will be a clone of your LVDS display and you can use xrandr within X11 to manage the screens as usual at least for some standard resolutions such as 1024×768 and 800×600. Typically those are sufficient to give a presentation on a beamer 🙂

You may also have a look at e.g. the Archlinux Wiki for a documentation about the Linux kernel mode settings.


  1. See e.g. this bug report:
  2. Obviously, this needs a reboot. As soon as GRUB comes up type ‘e’ to edit the parameters.