T420 - Can't use DisplayPort with integrated graphics

[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.

[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.

[Ezhik]

In that case, can I get rid of the Nvidia GPU? I don't mind replacing the motherboard if I have to.

[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.