Displayport/USB4 autodetection on tiger lake chromebook

There seems to be an issue with the current (and past) Tiger Lake chromebook EC firmwares where, even with the USBC fix on recent linux distributions, video is not automatically output via USB C. It can be enabled each time a monitor or dock is plugged using ectool, but this requires root and is a bit inconvenient. Does anyone know exactly what’s happening? It seems to affect a wide range of TGL chromebooks; I have CP713-3W like one of these posters, and am using Ubuntu 24.04 LTS with the most recent voxel firmware.

Any ideas what’s up?

See for example:

Maybe I should post this in the firmware bugs section? Im just curious if the root cause is known and this is an upstream and/or Linux issue or if this is just a bug that hasn’t gotten attention and maybe can be easily fixed. If it hasn’t gotten much attention, I may get stupid and start compiling/testing EC firmwares with changes I make that probably have nothing to do with the issue and probably brick my device :sweat_smile: (at least I have a suzy-q lol).

And actually that other CP713-3W user wasn’t me :). I haven’t posted here before.

AFAIK this is an implementation issue with Chromebooks, in that the kernel needs to notify the EC when a USB device is connected so that it can enable the required features (because on Chromebooks the EC is acting as the USB-C mux controller, rather than it being handled automatically by a separate chip). There’s nothing I can do from the firmware side to work around that. I also don’t know what recent “fixes” have been made upstream.

Ah, thanks for that. I was under the impression that somehow the EC firmware wasn’t properly detecting the displayport presence (thinking maybe a gpio config or something). Guess I was way off base and need to learn more about low level interactions to better troubleshoot.

Thanks Mr. Chromebox, really appreciate the insight.