Comment # 6 on bug 1207776 from Patrik Jakobsson

Looks like the machine has both intel and nvidia graphics. I would suspect the
external connector is attached to the nvidia gpu. And it seems you have the
"open" nvidia driver installed which doesn't support your gpu:

[   14.121892] nvidia 0000:01:00.0: enabling device (0006 -> 0007)
[   14.126777] nvidia 0000:01:00.0: vgaarb: changed VGA decodes:
olddecodes=io+mem,decodes=none:owns=none
[   14.126802] NVRM: The NVIDIA GPU 0000:01:00.0 (PCI ID: 10de:13b0)
               NVRM: installed in this system is not supported by open
               NVRM: nvidia.ko because it does not include the required GPU
               NVRM: System Processor (GSP).
               NVRM: Please see the 'Open Linux Kernel Modules' and 'GSP
               NVRM: Firmware' sections in the driver README, available on
               NVRM: the Linux graphics driver download page at
               NVRM: www.nvidia.com.
[   14.126870] nvidia: probe of 0000:01:00.0 failed with error -1
[   14.126906] NVRM: The NVIDIA probe routine failed for 1 device(s).
[   14.126909] NVRM: None of the NVIDIA devices were initialized.

Adding Stefan to CC.
Stefan, should this card be supported by the new nvidia driver?