In the context of the Linux kernel, you've never truly nailed down the functionality of the old thing. Interfaces external to the driver evolve over time (which

In the context of the Linux kernel, you've never truly nailed down the functionality of the old thing. Interfaces external to the driver evolve over time (which bleeds into changes internal to the driver), requirements change, people want to add new features that old hardware ought to support -- all this adds up and puts evolutionary pressure on the drivers. Code duplication really hurts here. It's possible that the AMD developers are from a Windows culture where they don't have to worry about this because Microsoft gives them a stable interface. Though even there, I find it questionable whether it's a win. Surely the occasional bug will surface that affects drivers for older hardware as well?