IP law is that you can patent a mount (or any legal object) but you cannot patent attachments to that mount. So, any third party manufacturer can legally make a lens mount that fits on to that mount. The same is true for vacuum cleaners or any other device.the physical mount itself is patented.
not to mention the base protocols.
"AF specific"? I mean there is some patents that deal with the lens based algorithms, I guess it depends on how much they copied from Canon or mimicked.
but it probably wasn't worth the fight for Viltrox as you mentioned
IP law allows anyone to reverse engineer a protocol legally. However, if the reverse engineering is actually based on illegally seeing a patented or secret protocol, it is illegal (as alluded to by @koenkooi that Viltrox may have done).
The consequence is that Viltrox and everyone else can legally make manual AF lenses for Canon RF lenses and no way can Canon stop that by law. For AF lenses, they need to design their own communications protocols without seeing Canon's.
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