HP Elitebook 845 G8 not passing Displayport over USB-C via Caldigit TS4 Dock

[atjbramley]

Hi!
I'm already in discussion with CalDigit over this, but thought I'd come this side too to see if I could find an answer.

My girlfriend and I share a desk, and we're after single cable Nirvana - charging, peripherals, monitor...  I use a TB4 enabled Macbook Pro, and she uses an HP Elitebook 845 G8 with Radeon Graphics. 

We purchased a Dell Ultrasharp U2723QE 4k - which has a USB-C port that features numerous inputs:

• Displayport 1.4 over USB-C
• Displayport 1.4
• HDMI

We also purchased a CalDigit TS4, which supports both Thunderbolt and USB-C connections.  The applicable outputs of the TS4 are:

• USB-C/TB4
• Displayport

With the macbook - everything works.  I can connect to the monitor directly via USB-C or HDMI and everything works.  I can also connect via TB4 cable to the TS4 and then to the monitor by either Displayport or USB-C and everything works.

With the HP Elitebook 845 G8 I can connect directly to the monitor via USB-C and everything works.

The problem is that we cannot connect via the TS4.  Going via the USB-C output gives peripherals only - but no display.  Going via the Displayport output gives nothing.

Was just wondering if there was any known limitation of the graphics implementation in this notebook (I've seen talk about how it behaves differently depending on how much RAM is installed?), and also whether and additional drivers/software need installing.

Any help much appreciated!

[banhien]

@atjbramley 

Definitely they are NOT compatible.  Please review the following list and compare pro/con few options before make final decision.

                  https://www8.hp.com/h20195/v2/getpdf.aspx/c04168358

Regards.

[atjbramley]

Hi,

Thanks for your response, but I need more detail.

The link you've supplied only lists HP docks.  Can you specify where it is stated that HP laptops are only compatible with HP docks?

On the otherhand, the first dock in that catalogue (HP USB-C dock G5) uses the same technologies as the dock that I have purchased (USB-C to host, Displayport 1.4 to the monitor.  Page 39 specifies that this dock is compatible with the Elitebook 800 series.

Is there some kind of limitation that limits HP laptops to only HP docks?  If not, then both this and my dock (and any other dock with the same underlying technologies) should work.

[atjbramley]

I've done some more testing and the issue was the Apple 3m Thunderbolt 4 cable I was using between the HP and the Caldigit TS4.  I can confirm that the dock works fine when using a 0.8m TB4 cable.

I guess I now need to look into why the HP laptop won't work with the 3m TB4 cable, which is the length I need - the laptop is about 2.3m away from the dock.  Possibly to do with HDCP timings caused by the extra length? 

[atjbramley · Accepted solution]

I figured it out.

The 3m Apple Thunderbolt 4 cable didn't support MST with the HP Elitebook 845 G8. 

Solution was to start up the monitor via the short TB4 cable, select MST mode off (which was otherwise greyed out), and then connect up again via the 3m cable.  Everything then functions as it should, including 4k@60hz & all peripherals. 

I don't have a need to daisy-chain monitors, so I'm happy with this limitation.  Hope this helps somebody in the future!