While the other Knicks were going through a light workout, J.R. Smith was on his own. He was working furiously with trainer Idan Ravin, running baseline to baseline, sinking one jump shot after another. It was the final dress rehearsal for Smith before the enigmatic shooting guard makes his regular-season debut Sunday against the reigning Western Conference champion Spurs. “I can’t wait,” Smith said after the workout, sweat dripping from his brow. “It’s going to be a big game.” A lot has happened since Smith last played in a meaningful basketball game. He was suspended five games for violating the NBA’s anti-drug policy for allegedly testing positive for marijuana. He underwent patellar tendon surgery and arthroscopy on his left knee shortly after inking a three-year, $18 million contract with the Knicks. “I just want to do so well for my teammates,” said Smith, who played in the team’s final exhibition game. “I feel like I’ve not really been a part of the team, but still being a part of the team is tough. You can’t get out there physically and help these guys. You can only do so much from a communications standpoint. …. There’s only so much you can do from the sideline. [I’m] just happy to get it over with.” Last season’s NBA Sixth Man of the Year will come off the bench in his return, Knicks coach Mike Woodson said. Woodson didn’t specify whether Smith will permanently be in that role, but Woodson wanted to keep the status quo after Friday’s 101-91 victory in Charlotte, meaning Iman Shumpert isn’t headed to the bench, at least not yet.