Just to clarify what I was saying, I would bet money that Rembrandt
does support DisplayPort and PCI Express tunneling as well as Thunderbolt Alternate mode. However, these are all optional features for hosts per the USB4 Specification, and I have yet to see anything that constitutes confirmation from AMD that these capabilities are in fact present in Rembrandt.
They could have designed it themselves or more likely using Synopsys
The DesignWare USB4 IP is the leading IP solution based on the USB4 specification from the USB Implementer Forum.
www.synopsys.com
TBT4 is not covered in USB4 spec. Only TBT3.
From Spec only this mentioned
Linux driver (written by Intel) detected XDomain, PCIe Tunneling, DP tunnelling for RMB so the silicon should have it.
But like mentioned, AMD very likely would not want to put Thunderbolt sticker on their chip. They can always say Fully USB4 compliant, then OEM can decide what to do with their device if they want to sent to Intel for certification to get that sticker.
But for the future not sure, what will happen if Intel moves on to TBT 5 with 80 Gbps, when AMD get enough market traction they might split the ecosystem which would suck. Apple likely would do the same.
AMD may well have followed Apple's lead and used Synopsys IP for their integrated USB4 host controller solution, but my point was slightly different.
Every Thunderbolt and USB4 peripheral device currently on the market uses discrete controllers purchased from Intel. The existing ecosystem is entirely based on Intel silicon, and interoperability with those devices is where the value proposition lies for most consumers.
Furthermore, in order for OEMs to add Thunderbolt / USB4 support to a Rembrandt platform, they need to implement several additional components (Type-C port controller, USB PD controller, and Thunderbolt / USB4 retimer). Until recently, Intel was the sole source for the retimers. However, it looks like as of last quarter,
Parade has announced a suitable retimer and
NXP has come out with a linear redriver.
Because additional components are required, AMD can't simply slap a "Thunderbolt 4 Certified" sticker on their APU. And another reason they can't do so is because OEM's can route those signals however they choose. For instance, it appears that ASUS didn't want to deal with retimers or Thunderbolt / USB4 certification for the
ROG Zephyrus G14 (2022) GA402 and instead utilized those signals for 10Gbps USB 3.2 Type-C ports with USB PD and DisplayPort Alt Mode.
To be fair USB4 was defined based on TBT3 when TBT4 didn't exist yet. Also my impression is that the
differences between TBT3 and TBT4 are such that reaching feature parity is not unsurmountable.
In order to understand the differences between Thunderbolt 4 and Thunderbolt 3, you need to understand the differences between USB4 and Thunderbolt 3, which are much better summed up in the Thunderbolt 3 Compatibility section of this document:
https://www.usb.org/sites/default/files/D2T1-3 - USB4 Time Sync - Host Interface - CM - TBT3.pdf
And here's a link to all of the USB Developer Days 2019 presentations, many of which are quite good (if you're into that sort of thing):
https://www.usb.org/documents?search=&category[]=64&items_per_page=50
Yeah, it is definitely possibly but cannot claim compliance though because I am not sure Intel will allow to put its exclusive sticker (Just going spec wise I don't really know if Intel VT-d can be certified with AMD-V, but rest seems doable in firmware and external circuitry outside of SoC)
At this point it seems Intel wants to keep TBT4 to itself, TBT3 compatibility seems more due to pressure from others or fear of fragmenting the ecosystem.
But USB4 seems enough though, so personally I don't care about TBT4. PCIe tunneling, DP tunneling, Charging/PD, 40 Gbps USB are enough for almost all use cases.
As you say, the certification really doesn't matter here. What does matter is working support for those items you mentioned. But I'd also add Thunderbolt Alt Mode to that list, because almost all of the devices you'll want to connect to initially will require it. That might change once USB4 device silicon takes off, but there's currently a ton of Alpine Ridge devices out there that won't work with a USB4 host without Thunderbolt Alt Mode.