Following in the risqué footsteps of HBO’s “Hung” and Showtime’s “Secret Diary of a Call Girl,” HBO has a show in the works about the pornography business. “Entourage” and “Boardwalk Empire” executive producers Mark Wahlberg and Steve Levinson are working with controversial writer James Frey — whose next book is titled “The Final Testament of the Holy Bible” — on a one-hour drama that will use both legit actors and real porn performers. The plot will focus on a giant video company under siege from Internet competitors and a girl from the Midwest whose boyfriend convinces her to move to Los Angeles to become a star. Reached by Page Six, Frey, who’s writing the pilot, said, “We’re going to make a sprawling epic about the porn business in LA. We’re going to tell the type of stories no one else has told before, and go places no one has gone before.” Very private places, we imagine.