Essentially all the supposedly merchant SoCs are proprietary. Instead of shipping data sheets, winbond or mediatek want to ship you a reference design with reference linux or android build that only works because of a huge binary blob.

There’s a small hardware consulting company in Palo Alto whose main differentiator is that they have a bunch of folks in China who manage to generate docs they can use. I’m guessing this involves a lot of under the table leaks and late night alcohol-fueled discussions.