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02-03-2020 06:05 AM - edited 02-03-2020 06:07 AM
Product: HP ProBook 440 G6, USB-C Dock G5, HP z27
Operating System: Linux
How do I get USB-C Dock G5 to support 4k 60Hz over DP? The support for that is stated in the promo materials and documentation. Connecting monitor directly via a USB-C cable allows 4k 60Hz, but via dock I can only get 4k 30Hz. Do I have to update the dock firmware or something?
9 REPLIES 9
02-09-2020 04:43 AM - edited 02-09-2020 07:25 AM
I was wondering if anyone was able to solve this problem.
On paper, my laptop (Lenovo S540-13IML) should support 4k output @ 60 hz (at least it says so in the spec sheet), however I only get 4k @ 30 hz when connecting an external display through any of the DP or HDMI ports.
03-12-2020 11:48 AM - edited 03-12-2020 11:59 AM
Just wanted to +1 this issue. I've tried connecting my Pixelbook (DP alt mode) and Dell XPS 13 9350 (Thunderbolt) to a single Dell P2715q 4k monitor via this dock and am experiencing the same 30hz cap. The Pixelbook works fine at 60hz with a passive USB Type-C to DP adapter.
I also tried an Asus Chromebox and a Surface Go with the same result, though I'm less concerned about those.
I've tried updating the firmware but it didn't seem to change anything.
03-13-2020 04:40 AM
Actually, taking a closer look at https://www8.hp.com/h20195/V2/GetPDF.aspx/c04168358 I can see that it should theoretically support 2x4k@60Hz with dp v1.4, so there might be the same issue in your case as well.
From what I can tell, there is either USB 3.1 + 4k@30Hz or USB 2.0 + 4k@60Hz, but it is unclear how to control this since the dock itself has no switches and no driver to do that via software controls is provided. Maybe windows can somehow control it out of the box, I don't really know since I use Linux on my laptop.
03-13-2020 08:35 AM - edited 03-13-2020 08:58 AM
I think your second paragraph is spot on, but to add a more detailed explanation I found https://www.dell.com/community/Laptops-General-Read-Only/Demystifying-USB-C-and-Thunderbolt-i-e-adap... (specifically the #3 heading) that explains most of the mechanics we're seeing. In my case I think my devices only support DP 1.2 though most spec sheets seem to gloss over this.
If my understanding is correct, then https://www8.hp.com/h20195/v2/getpdf.aspx/c04168358 is wrong to imply that "DP 1.2 MF" supports a single 4k display at 60hz.
It sounds like it would be technically possible to create an alternate dock firmware that would force a 4-lane DisplayPort connection. In my specific situation, that would be the ideal compromise.
Also it's unclear to me how exactly this dock supports Thunderbolt. It's mentioned on the product page but also says "Thunderbolt™-enabled notebooks will function at USB-C™ speeds" which I figured didn't apply to video.
Does linux make it easy to force 4-lane DisplayPort yourself?
03-13-2020 09:34 AM
No, I haven't found any way to configure USB port to use specific standard, some reddit threads state that USB version is defined by hardware and there is no need to reduce support since it's backwards compatible with USB v2 hardware anyway.
There is a possibility that alt mode drivers in kernel provide some way to control it though. In case with the monitor I use right now, it has a switch in the settings: use USB3 + 4k@30Hz or USB2 + 4k@60Hz, but the dock has no such option or it is not obvious how to control it. The table in the product sheet (and the setting in earlier laptop versions BIOS) kinda point towards it being host-controlled as well. But sadly, I don't have direct access to my laptop's BIOS to test options there.
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