UM5304TA does not seems to support USB4, as I've learned the hard way, and I'm fine with it. However, the implementation which disables USB4 is buggy, as it also bans USB4 devices with USB3 support. My CalDigit TS4 dock is USB3 compatible, and it can be used perfectly with just an A to C cable, but it fails to be even enumerated on my UM5304TA.
When I plug the dock directly to the computer, nothing happens. Dmesg shows nothing (I use Linux), and the LED on the dock remains dark. However, if I plug the duck using C to A adapter then an A to C cable, it works fine, albeit without PCIe tunneling capability and display output capability, which is a PITA. I do not care about PCIe anymore, but DP over Type C should be supported, but clearly on this machine it doesn't, unless your device is USB3-only and does not advertise USB4/TBT3 capability at all.
This leads me to believe the lack of USB4 support is not a BIOS decision, but a deliberate disabling. The type C port controller (likely a TI or Cypress chip every 2 ports) is likely being installed a firmware which rejects all devices advertising TBT3 capability from enumerating. Asus can decide what feature to open to the user, but if you want to neuter a feature, please at least do it correctly.
Not only USB4-specific features don't work, this device refuses to work with USB3 and 4 compatible devices too. This is a serious bug, please fix it. I'm not asking for USB4, I'm asking for proper USB3 with DP alt mode support on USB4-capable but also USB3+DP capable devices (basically, all JHL8440-based docks). They work fine on strict USB3 ports on other computers and phones.
Regards,
B.G.
