usb on linux

Hi..
I am working windows device drivers, now i have to work on usb device
drivers on linux,
i have some doubts on usb architecture in liux, i have gone through
your documents, still i have some doubts, i think u can solve my
problem.

i have a small knowledge on usb in windows drivers,
1)like windows in linux how the driver and device stack will form? and
what is the role of pnp manager in linux?
2) what is the role of I/O manager in linux, whether the pnp manager
will exist in linux or not?
3)in case windows we use many filter drivers , like that can we have
any filter drivers concept in linux drivers?
4)in case of windows usb drivers enumaration starts by sending irps to
the hub drivers and pnp manager, the same things will happen in linux
also?
5) what is difference in enumaration in linux and windows?
can u give a very good sites or groups which can help me out for
writing drivers for usb.
 
thanks and regards
 
shankar