I never had any problems with vbox usb passthru from lin.host to win.guest, so you might have a really specific case here, but I know there are loads of people running
qemu on lin.host with all kinds of advanced hardware pass through configurations.
Thinking about it, if you have a very old motherboard the IOMMU layout might have hindered proper hardware separation.
Comments
My experience for generic Virtual Serial Port hardware
* MacOS Parallels - Abysmal performance, constant USB timeouts. Virtually useless
* Virtual box on Windows, emulating Windows - Able to detect device, but unable to talk to it.
* Virtual box on Linux emulating Windows - USB does not even detect.
I never had any problems with vbox usb passthru from lin.host to win.guest, so you might have a really specific case here, but I know there are loads of people running qemu on lin.host with all kinds of advanced hardware pass through configurations.
Thinking about it, if you have a very old motherboard the IOMMU layout might have hindered proper hardware separation.
But I doubt OP really need pass-through at all.