1

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?

2

The simplest cause is usually the easiest - the confusing bundle of cables on this hot desk, once untangled, revealed that the DisplayPort cable was not plugged in.

Now, when connected, kern.log tells me:

Nov 19 14:36:02 GTA-65 kernel: [17099.717660] [drm] Reducing the compressed framebuffer size. This may lead to less power savings than a non-reduced-size. Try to increase stolen memory size if available in BIOS.

So Linux kernel 4.19 does support alternate mode for USB-C to Display Port

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