It's not so much a fundamental technical limitation as in a large amount of work in FreeBSD for almost zero return - maybe a fundamental resource limitation.When there is no fundamental limitation,Is that a detail of the current implementation, or a fundamental limitation in the bhyve architecture?Only two choices ? :) Maybe half way between those points.
i.e. when a future version of the hypervisor may be able to support the feature with no changes to the firmware, then it would be good practice to leave the drivers enabled. Doing so avoids creating an unnecessarily tight coupling between the hypervisor and firmware versions.Well versed in those issues :)
More importantly: does it even matter that the hypervisor doesn't support passthrough of PCI legacy interrupts? UEFI operates on a polling basis, with the only active interrupt being some kind of periodic timer. Where do you see any requirement for legacy interrupts in the UHCI/EHCI drivers?It creates a case where the o/s booted by EFI isn't able to use those controllers as expected.
Anyways, this is more a discussion for the freebsd-virtualization mailing list if you'd like to chat about it more.