I initially though, due my own short tests with Rembrandt that it would not have a 2nd DP Tunnel at all. But there are some users here that reported 2 displays with for example a CalDigit TS4 on an AMD FW13. Sadly, I have never gotten any of them to give me a Windows diagnostics dump that would allow me to double and triple check if there is no miscommunication and those people use weird hardware with DisplayLink or are hiding facts from me. A few Redditors also reported it just working as expected with docks that have no MST.
The full USB4 panel should do. To exclude most weird stuff in 3 situations:
- Without any DP connected (no MST hubs either)
- with a native DP output connected & active
- with a tunneled DP output connected & active.
Here my ADL-P TB4 as example. The DP In Adapters shows 2 for this controller (which for Intel has 2 ports. Both on the same side with FW). “Tunneled DP IN Adapters” counts exactly what it says, active DP connections through USB4/TB3. And “Unavailable DP IN Adapters” counts if they are made unavailable by for example native output which does bypass the USB4 router, and still makes it unavailable for the 2nd tunnel / port. This should indicate if some outputs are shared somehow. And multiple ports in the same controller should always share their DP In adapters.
And if you really want to go hard, you can enable the the “Device Portal” in Windows Developer Settings. (Should require installation and a reboot to actually start the webserver whenever the system booted with the option disabled). That shows the full graphic that would also be perfect to 100% confirm the use of the 2nd tunnel if a device is connected that does. Here is an example of that (with a topology of 3 TB3/USB4 devices connected: Caldigit Element Hub - Goshen Ridge, Dell WD19TB -Titan Ridge, Anker 556 - Via VL830)
It shows nicely how the tunnels are routed and which In/Out adapters are used and which are still free. Native output will bypass the USB4 router, so will never be visible in this graphic. And it will not use a “USB4 DP In Adapter” either, even though with Intel, the incoming DP connection will be unavailable if its used that way.