kernel linux

Hi, everybody

I’m a student and for thesis i have to describe every function that the kernel calls, when an usb is connected.
At the moment i’m working well using printk on each core’s file.
I’ve seen that every connection of usb key, starts with the call “usb_hcd_irq()”.

My question is which are the functions that calls usb_hcd_irq()?

Another trouble is what’s the first function that is called when the pull-up of usb port became high?

Thanks, in advance.