[SOLVED] 4k@60Hz through USB-C

[unbecomingseedling]

Hi guys,

I have a Huawei Matebook X with a single USB-C out port, and am trying to connect it to two monitors, one at 4k@60Hz and another at 1080@60Hz.

When I use a USB-C to DisplayPort cable, I manage 4k@60Hz, however this doesn't suffice since I also have the second monitor and peripherals. Hence I need a USB-C hub, however the moment I introduce a hub, I only get 4k@30Hz. Even a top-of-the range hub such as this which advertises 4k@60Hz only does 4k@30Hz with my laptop, and I have tried 3 other similar hubs which all fail to do 4k@60Hz. (I'm using DP to DP when connecting hub to monitor)

I don't understand why connecting directly to my laptop gives 60Hz but when I introduce a hub that is advertised to pass through 60Hz it fails...

Would appreciate some help!

 

[Barty1884]

I don't understand why connecting directly to my laptop gives 60Hz but when I introduce a hub that is advertised to pass through 60Hz it fails...

Bandwidth, probably.

Do you drop to 4K/30Hz when connected only to a single display via the hub?

From the product notes:

1. Only one video output is supported at a time.

So it should pass through 4K/60Hz as the only display connected.

2. Available with select PC models (with support for DisplayPort Alt-Mode 1.3 & above standard) when connected to displays that offer 4K resolution at 60Hz. Otherwise, default
resolution will be 4K at 30Hz.

Give you can go straight USB-C to DP at 60Hz, your device's USB port can do it, but it's going to depend on the standard implemented whether it can do 4K/60Hz + peripherals.

 

[unbecomingseedling]

Thanks for the reponse Barty.

Indeed I dropped to 4k@30Hz even when connected to a single display. Is there really a difference in hardware standard that distinguishes supporting 4k@60Hz and 4k@60Hz + peripherals? I'm hoping that it's some sort of software/driver issue since the former doesn't seem too likely (judging by the fact that it works direct, I can assume the port supports Alt-Mode 1.3+)

 

[Barty1884]

Theoretically, there could be - and given the hub specifically states "only one video output", I suspected if you had the single display connected and no peripherals, it should still pass through 4K/60. Clearly not the case.

Writeup on the topic found here:
View: https://www.reddit.com/r/MatebookXPro/comments/auafyh/overview_connect_your_matebook_to_an_external/


Looks to be, because of the presence of USB, the output is not dedicating all lanes to DisplayPort... which is pretty much what I expected (although I thought those lanes wouldn't be 'reserved', only when in use).

TB3 dock should achieve what you need, but they're pricey (although less pricey than the time the writeup was done).

 

[unbecomingseedling]

Many thanks again, the lane configuration info is very interesting.

For any future readers, since the Matebook X (non Pro) does not support TB3, only option 2 applies (very expensive though). Only having a single DP1.3 USB-C port turns out to be too restrictive