And USB4 (no space…) includes a Thunderbolt 3 compatibility layer. But USB sub-standards are a dog’s breakfast.[1] I would expect the USB part of USB4 to work; but the Thunderbolt 3 part may not get more attention and better support on Linux than TB 3 got in the first place.
Then, shortly after Maple Ridge TB4 controllers were released, Intel damaged its own standard by removing TB 1 and TB 2 support from Maple Ridge through a Thunderbolt firmware update (NVM 36), packaged in motherboard BIOS updates and not downgradable[2].
So, while Apple users can now enjoy their legacy TB1/2 devices on their Apple Silicon Mac (with adapters) because Apple makes its own Thunderbolt controllers and still maintains full compatibility, Intel users now have to interpose a Titan Ridge (TB 3) dock between their Maple Ridge TB 4 controller and their legacy TB 2 audio interface… I suppose Intel saves on compatibility testing and that no Windows user complained because Thunderbolt is not used on Windows. And how’s that going to evolve with Thunderbolt 5 is anybody’s guess.[3]
That’s all the point: Thunderbolt 4 controllers do USB4; USB4 controllers do basic Thunderbolt 3, but not Thunderbolt 4 (=Thunderbolt 3 with all optional features).
ASM4242 is a “USB4” controller that is actually designed as a full TB 4 controller but was released without official Thunderbolt certification. Whether ASMedia eventually gets certification is an open question.
USB 3.0 (with space…), USB 3.1 Gen1, USB 3.2 Gen1, USB 3.2 Gen 2, USB 3.2 Gen2x1, USB 3.2 Gen2x2… Fancy a quizz? Which modes are not supported by the USB compatibility layer of Thunderbolt controllers? The x2 modes. ↩︎
well, not without a special downgrading BIOS from the manufacturer (9901 for some Asus Z690 boards). ↩︎
My guess: Windows users will, eventually, get Thunderbolt 5 docks; all other Thunderbolt devices will be designed and marketed solely or primarily to Mac users. ↩︎