On Thu, May 26, 2016 at 11:01:31AM +0530, Narasimha M wrote:

Hi, Thank you so much for your help. One last query in this. From you
explanation USB host controller will receive the packet from device. So could
you please tell me, what is the first function being called when device gets
the data

Which device?  The host controller?  Or the driver for the USB device
itself?

and if I am not working this first function will be in USB host
controller code.

The host controller gets the data first and then passes it to the
specific USB device driver.

Again, usbmon is going to be the best thing to use here, good luck!

greg k-h