The problem for hardware manufacturers is that they think their drivers are valuable trade secrets and don't want to mainline them into the kernel...
Again, this is by design to try and force manufactures to open their driver code. To me, that seems like a lost cause now thanks to the proliferation of binary blobs required for hardware anyway.
> So, if you have a Linux kernel driver that is not in the main kernel tree, what are you, a developer, supposed to do? [...] Simple, get your kernel driver into the main kernel tree (remember we are talking about drivers released under a GPL-compatible license here, if your code doesn't fall under this category, good luck, you are on your own here, you leech).
In order for a driver to be in-tree, it has to be open.
Incidentally, this document is full of the kinds of arrogant and user-hostile arguments that the Linux community is known for, for example: "You think you want a stable kernel interface, but you really do not, and you don't even know it."