linux kernel interfacing with USB host

Hello,

I'm working on a project with a Motorola Dragonball i.MX1. It has no
native USB host ( only a device ) support, so we'll be needing to put
in a separate chip on the bus of the MX1 and port over the linux usb
host drivers. The MX1 uses a port of the linux kernel 2.4.18.

Could anyone help identifying specific source files/functions for the
linux usb host drivers that actually interface with the I/O of the
chip? ( This is what I'll have to work on to port a usb host chip to
the MX1 )

thanks much!