USB3 connection without USB2

I am developing an embedded system that has a Jetson TX2i and another ARM Linux processor system (Xilinx Zynq) on the same board. They will communicate with each other with a USB connection. Both devices support USB gadget mode so I could make either one the host/device. Here is a block diagram of the two devices:
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This diagram shows the Zynq as the OTG host but obviously the roles could be reveresed.
As you can see the Zynq requires an external ULPI PHY, while the Jetson has this built in. In practice, I only really desire the high speed USB3 connection. I want to implement this system with the least number of components/complexity. Want I would like to know is if I can eliminate the PHY and have the system look like this:
image
Is this possible? Is there some limitation that prevents USB3 from working in the absence of USB2? Is this limitation in the driver implementation or is a hardware limitation? I realize you likely cannot comment on the ability of the Zynq to support this configuration but can you answer specifically for the Jetson? I know in theory USB3 can work without USB2 since USB3 enumeration is independent of USB2 (one source). Thanks for any input.

Hi, from HW side, we can only support the designs as listed in TX2 Design Guide. The design without USB2 is not in the reference, so it can’t be guaranteed.

I would like to add that a USB3 device, if upon plugin works as USB3 (not all USB3 signals will have sufficient quality), then it will never revert to USB2. In the old days one would have a single USB2 controller and this would also handle legacy modes for USB1.0 and USB1.1, but with USB3 it starts with a dedicated USB3 controller and actually routes to a different USB2 controller if the signal quality is insufficient (or if the device in question can’t handle USB3). Thus I suspect (no guarantee) that lacking a routing to a USB2 controller would only be harmful if the device was unable to handle USB3 speeds.

I also suspect you’d have fewer quirks if the Zynq is in device mode and the Jetson is in host mode.

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Thank you both for your input. I will try to devise an experiment with carrier boards to test this configuration and let you know my findings.

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