Pro Display XDR as USB-C Dock?

[joevt]

I finally got my hands on this dock after a lengthy preorder wait. Unfortunately it seems it's only supported in macOS 11.1 & above, but I've stayed on Catalina because I saw you post that Big Sur broke DSC. Any advice for what to do now? 🤔

I did some testing of the CalDigit Element Hub which is similar to the OWC Thunderbolt 4 Hub. It has very limited support in Catalina. Thunderbolt devices and displays must be connected before boot and cannot be hot plugged. You can hot plug USB devices though. Only one display will get enabled though in this case. Even with Big Sur, a second display connected to the hub is not enabled until after it is hot plugged.
https://forums.macrumors.com/thread...ts-and-four-usb-a-ports.2283180/post-29718129
I suppose it could be possible to create an EFI driver that enables the second display before the OS boots. Also, a macOS driver that enables displays connected to a Thunderbolt 4 hub when they are connected...

I am not sure about DSC being broken in Big Sur in all cases (such as the XDR). I would like to see more people test that. You can install Big Sur to a different partition or a different USB or Thunderbolt drive for testing. All I know is that DSC doesn't work in Big Sur with any of the DSC capable devices I have (using a W5700):
- Apple USB-C Digital AV Multiport Adapter
- CAC-1085
- CalDigit SOHO
- HP Thunderbolt Dock G2
- Delock 87737

For Catalina, the HP Thunderbolt Dock G2 120W is a Thunderbolt dock that has a USB-C DisplayPort Alt Mode capable port and a Thunderbolt port - both of which can connect a USB-C display. I don't know of any other non-Thunderbolt 4 docks with two USB-C display outputs. I suppose if a dock has a DisplayPort port instead of a USB-C port then you could use something like a Belkin Charge and Sync cable to connect a USB-C display (HBR2 + USB 2.0).

 

[swrobel]

I did some testing of the CalDigit Element Hub which is similar to the OWC Thunderbolt 4 Hub. It has very limited support in Catalina. Thunderbolt devices and displays must be connected before boot and cannot be hot plugged.

I tried booting Catalina with both displays (Pro Display & LG 22MD4KA) connected to the hub, and the hub connected to the MBP 16, but only the LG was detected at boot, probably because it's a USB-C alt-mode display. System information doesn't seem to see the Thunderbolt hub - only the USB-C hub.

I tried booting Big Sur 11.3 beta from a separate volume and both displays worked! Now to migrate over to Big Sur...

 

[joevt]

I tried booting Catalina with both displays (Pro Display & LG 22MD4KA) connected to the hub, and the hub connected to the MBP 16, but only the LG was detected at boot, probably because it's a USB-C alt-mode display. System information doesn't seem to see the Thunderbolt hub - only the USB-C hub.

Right, Catalina's not going to show anything that wasn't initialized in UEFI. The UEFI Thunderbolt driver will enumerate PCIe devices over Thunderbolt, including those connected to the Thunderbolt 4 Hub. Only one display gets initialized during boot (during EFI). I haven't tested a display connected to other Thunderbolt devices connected to the hub.

Catalina's Thunderbolt drivers don't know how to deal with the Thunderbolt 4 Hub so it won't appear as a Thunderbolt device, nor will other Thunderbolt devices connected to it, but the PCIe devices enumerated by UEFI remain in the ioregistry and are usable. System Information.app will show the USB bus of the Thunderbolt Hub, and will show PCIe devices in the Hub and connected to the Hub.

In Catalina, System Information.app shows in the Thunderbolt tab that there's a proper connection (Link Status: 0x2, Speed: Up to 40 Gb/s x1, Current Link Width: 0x2) but says "Status: No device connected".

Maybe the only issue that Catalina has is the different format of the DROM in the hub. I haven't checked the format of the DROM yet. The USB4 spec has information about the expected formats for the DROMs used in USB4 devices as well as USB4 devices that are compatible with Thunderbolt.