It looks like I'm only partially right: dummy_hcd is just for the local kernel, ...

It looks like I'm only partially right: dummy_hcd is just for the local kernel, but raw gadget is just yet another interface to the UDC, so like usb functionfs just without sanity checks.

I found documentation about this in the submission to mainline: https://lwn.net/ml/linux-usb/461a787e63a9a01d83edc563575b858...