My professor keeps opening my office door without knocking at the door Is it polite when my professor keep opening my office door without knocking at the door whenever he wants to ask anything?

Since the door closed, I am supposed to hear knock before breaking into, or rather, busting into the room. Is it polite?
Ethical yes. Polite no, it is not. I do not see what ethics (resolving human morality) have to do with opening the door. 

On a philosophical level, ethics and manners are kind of incompatible since they deal with a different nature of question.