Single USB driver, multiple devices, how many driver instances?
 

Does anyone know how the system handles loading device drivers when multiple, identical devices are connected? For example, if I connect multiple USB devices are there multiple instances of the appropriate driver loaded? This has come up because I am using modprobe to load a particular USB-to-serial driver (ftdi_sio) and need to support more than one product id. I've tried just invoking modprobe ftdi_sio vendor=0xNNNN but it doesn't seem to work. Normally I do a modprobe ftdi_sio vendor=0xNNNN product=0xMMMM but I want to plug 2 different products in at one time.

There is only a single instance, but it should recognize all the appropriate devices. There should be no reason to specify the vendor and product under normal circumstances.