Perform transient simulation of your USB serdes,
over a sufficient time to accumulate the data transmission
and reception over many bits.
In Hspice, depending on the wavefrom viewer tool you use, you
should be able to obtain an eye-diagram of your result
using the built-in function in the waveform calculator.
Otherwise you can super-impose a number of rising
and falling edges of your serdes output, by sampling the
waveform edges at periodic intervals starting from the
edge of one rising edge. The result will be your eye-diagram
of the PHY layer.
Hope this helps.
--Radigital