> I'm not sure if such a card exists. There are WiFi cards with free
> OS drivers (e.g. ath9k), but I would expect them to run some sort of
> firmware, too

according to wikipedia this ath9k family of WiFi controllers have both
drivers and firmware as opensource. About USB controller, I didn't add
xhci firmware image to my g505s coreboot and all the usb ports are
working fine although at usb2 mode - so it seems to me that at least
some controllers could function without a firmware, just that
functionality could be degraded without one