The thing is, despite RMS touting it of course, most of the GPL is completely irrelevant to hardware designs. Please consider choosing a simpler license. For most design files a CC-BY-SA license will have the same effect and the intention will be much clearer. If you want to make explicit patent grants the Apache is actually a good fit. There is even a modified one aimed at digital fabrication which let's you specify that a certain mark has to be included if copied and fabricated [1].

GPL is good for software, HDL and circuit masks only. I have seen a lot of debate around what one is allowed to do with GPLed PCB footprints. Bit of a pain in the ass really.

[1]: http://web.archive.org/web/20130718051941/http://jipel.law.n...