I use Ubuntu 18.04 and upgraded to Linux kernel mainline 4.19.2 with ukuu, which purportedly supports DisplayPort alternate mode for USB-C.
alex@gta-65:~$ uname -a Linux gta-65 4.19.2-041902-generic #201811132032 SMP Tue Nov 13 20:34:19 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
Other USB-C devices work fine on this Lenovo X270. However alternate mode doesn't kick in when my generic dongle is inserted, which works fine with a colleague's Windows PC; no events are generated in kern.log & dmesg.
Is there something I need to look into further, or another display-related library I need to update to have this working?