Drive up to the port as you normally would, but instead of driving into ticketing and passport control, follow the signs for parking: turn right and go around the roundabout to the parking/ticket office area. There are signs for this when you come off the motorway. Drive all the way to the passenger terminal at the end, where you can park in lot P5 for free for up to 30 minutes and drop off your passenger.
The place indicated in the link below is not the closest you can get without taking your car on the ferry. It seems to be the pedestrian entrance for those who are not arriving at the ferry by car. Google Maps indicates a bus stop nearby, but I see no evidence of that in street view:
Furthermore, this spot doesn’t have a good place for a car to stop, so you’re better off following the directions in Michael Hampton’s answer.
Credit:stackoverflow.com‘