Worth a read

Quite. Arm sell designs, 2nd parties use those to make chip designs, and 3rd parties then use _those_ to make platforms. So ARM itself has no real handle on how many actual board designs/platforms there are out there or what software is running on them. It does get data on chip shipments so royalties can be paid, but that's the closest it gets to knowing what's being done.

And yes - this diversity and the independence of downstream companies/devs is a big part of the reason for the code duplication in the kernel. Organisations like Linaro are doing their best to re-centralise/co-ordinate and share the actual development precisely because the downstream widget-makers and SOC vendors have done such a poor job of upstreaming and not NIHing. (I quite understand why - I use to be a downstream engineer and I failed miserably to get most of my code into mainline too, even though I know perfectly well why it's a good idea).