> Even just keeping the driver compilable with each kernel release often took some non-trivial refactoring,

I realise that the kernel contributors themselves are mostly volunteers and as such can just do what they want, and writers of non-upstreamed drivers will need to get used to chasing trunk, but to me this sort of thing seems like a waste of human talent. once something works, it should never not work again. it seems to me that despite all the layers of cruft that we've accumulated over the decades haven't really helped much with this, in fact they probably mean more work just to stay still.