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T420 - Can't use DisplayPort with integrated graphics

Posted: Mon May 02, 2016 2:50 am
by Ezhik
Hi there, got a fancy new monitor (a Dell P2715Q), but I seem to be unable to get it to work properly.

My laptop comes with the NVS4200m, but I disable it since it is not compatible with OS X. However, when it is disabled, I seem to be completely unable to use the DisplayPort.

I checked with a Fedora live USB, and what happened was:

Integrated graphics: Monitor does not work. xrandr does not show the DisplayPort at all.
Nvidia Optimus: The monitor connects! Ports display in xrandr.
Dedicated graphics: The Fedora live USB goes to a black screen, can't see anything.

Edit: Also checked with a Linux Mint live USB, same thing - DP is not even present in xrandr when using integrated graphics.

Re: T420 - Can't use DisplayPort with integrated graphics

Posted: Mon May 02, 2016 7:35 am
by brchan
Other people have the same issue. It seems that the display port is hardwired only to the nvidia GPU, so you must use optimus or discrete modes to use the displayport.

Since Linux's optimus implementation (bumblebee) is still a little buggy, I would recommend sticking with discrete mode.

Re: T420 - Can't use DisplayPort with integrated graphics

Posted: Mon May 02, 2016 10:41 am
by Ezhik
In that case, can I get rid of the Nvidia GPU? I don't mind replacing the motherboard if I have to.

Re: T420 - Can't use DisplayPort with integrated graphics

Posted: Sat May 07, 2016 11:55 pm
by Ezhik
Alright, so, I went and replaced my motherboard with one that doesn't have the dGPU - everything works well! The dGPU is located to the left of the CPU, if you are looking at the motherboard with the fan being in the upper left. Make sure that the motherboard you get does not have a BIOS lock. Get some thermal paste.

Then follow the Lenovo guide - you'll be disassembling everything.