void parport_unregister_port (struct parport * port);
When a parallel port driver is forcibly unloaded, or a parallel port becomes inaccessible, the port driver must call this function in order to deal with device drivers that still want to use it.
The parport structure associated with the port has its operations structure replaced with one containing 'null' operations that return errors or just don't do anything.
Any drivers that have registered themselves using parport_register_driver are notified that the port is no longer accessible by having their detach routines called with port as the parameter.