I dont think you should do anything!
He is a teenage boy, and he is going to watch porn. And I think that is perfectly healthy. Boys need an outlet, and he is at the age now where these issues are going to start becoming apparent for both you and him. The best you can do is maybe get his dad to have a chat with him, about the boundaries of sex, sexual encounters with women, and of course, condoms if he is (or becomes) actually sexual active.
Menatime, start knocking before you go into his bedroom and keep in mind that he is becoming a young man
Good luck!