I still don't understand what is Tivoization and why Linus Torvalds did not like it. Can you explain to me the big idea of Tivoization?
Tivolization, named after TiVo that widely used it, is a practice of devices running free software, but placing restrictions (such as digital signatures) that block running modified versions of the software on the device.
An argument can be made (as Richard Stallman actually did), that such a device could redistribute the source code of the GPLed software it uses, but since a user cannot modify and recompile it so it's usable on the same device (since he can't digitally sign it). Thus, such a device may uphold the letter of the GPL license, but violate its spirit.
Linus Torvalds actually stated that TiVo's practice here didn't really bother him (e.g., in this correspondence on lkml from 2007):
The kernel license covers the kernel. It does not cover boot loaders and hardware, and as far as I'm concerned, people who make their own hardware can design them any which way they want. Whether that means "booting only a specific kernel" or "sharks with lasers", I don't care.
Linus has stated that he didn't like the anti-tivoization clause in GPLv3 because it fundamentally changes the GPL. The whole point and purpose of the GPL, in Linus' mind, is to make users of GPL software pay back to the community by making all of their improvements of GPL software available to the community under the same terms. That's it. With anti-tivoization, GPLv3 adds a completely new obligation that has absolutely nothing to do with this fundamental purpose. He has also stated that there is nothing wrong with GPLv3 in isolation, but to call it GPL version 3 and claim that it's like GPL version 2, only better, is decidedly wrong as GPLv3 is very different from GPLv2.
Source, from Q&A session with Linus at some conference in 2014: https://www.youtube.com/watch?v=PaKIZ7gJlRU