N900 Hardware USB PHY
The USB PHY is the physical layer controller for the USB port.
Hardware
The NXP isp1707a is used as the USB PHY chip. [1]. This rights to this part have been bought by ST-Ericson and some information is available in a brief marketing sheet.
There is no published datasheet for this chip. It may be available under another name.
A reasonably similar chip (compare chips: [2]) is the 1704 which has a datasheet [3]
It is connected to the battery charger chip and the N900 Hardware CPU.
Software
The USB PHY is only dealt with by the kernel.