I edited my last post before I read your new one.

I know the i2c can be accessed from userspace. But from what I have read from the SC16IS... datasheet so far, it only encodes/decodes IrDA SIR. So how would you encode/decode the IR protocols from remotes? It think this can then only be done in the OS.

The part about the kernel driver is needed for interfacing it with LIRC. But maybe its LIRC-driver, as I wrote above the fact that LIRC is moved to kernel confused me.