I was wondering if lens manufacturers like Tokina, Sigma, Samyang etc, need some sort of permission from camera manufacturers in order to produce and sell their compatibles lenses or if any company that has expertise and can can reverse-engineer the camera's capabilities is free to offer their compatible products ?
It seems this is strictly a legal question. Because it is easy to reverse engineer or google the pin interface between the lens and camera. I believe from a legal standpoint the answer is no. I have talked to the Canon engineering department about this topic. It would be helpful to talk to someone from a legal department.