about tibet entrance permit...

we are foreign students studying in Chongqing medical university, China.we are going to be graduated on july and planning to back home from Chongqing-Lhasa(by train) Lhasa-Nepal( by coach)
we will travel Lhasa for 2 days then go back.
sir,i would like to know do we need a recommendation from TRAVEL AGENCY besides Tibet entrance permit???we can speak fluent mandarian chinese.