The following events take place before the client driver is attached:
The PROM (OBP/BIOS) and USBA framework gain access to the device before any client driver is attached.
The hub driver probes devices on each of its hub's ports for identity and configuration.
The default control pipe to each device is opened, and each device is probed for its device descriptor.
Compatible names properties are constructed for each device, using the device and interface descriptors.
The compatible names properties define different parts of the device that can be individually bound to client drivers. Client drivers can bind either to the entire device or to just one interface. See Binding Client Drivers.