sifive-blocks | Common RTL blocks used in SiFive 's projects | Frontend Framework library

I'm not an expert in rocket-chip's Diplomacy, but from glancing at the code, I think makeIO and makeSink do fundamentally different things.

makeIO takes the BundleBridgeSource and materializes ports in the Chisel Module implementation for driving that source. There is the same method on BundleBrigeSink. I believe this method is the way you take either side of a Bundle bridge and interface with it in the actual Chisel part of the generator (as opposed to the Diplomatic part).

makeSink turns a BundleBridgeSource into a BundleBridgeSink. It doesn't materialize Chisel ports and it stays in Diplomacy world rather than in the Chisel world.

In the example from I2C you included, note how the part with makeSink is a trait to mix into something that extends BaseSubsystem, it's diplomatic. On the other hand, HasPeripheryI2CModuleImp which has the makeIO extends LazyModuleImp which is the Chisel part. One way to think about this is two different "views" of the same thing. Chisel and Diplomacy use different objects, thus i2cNodes (diplomatic) vs. i2c (Chisel).