Sorry missed this:
{ .name = "ab8500-codec",
.of_compatible = "stericsson,ab8500-codec",Why are we doing this? The MFD cells are a totally Linux specific thing, there's no reason to represent them in the device tree unless they're in some way reusable and the "ab8500-codec" name suggests that's unlikely. Just put the properties on the parent node and instantiate the MFD cell as normal.
We have all of the AB8500 devices into the Device Tree to accurately represent the hardware. We will also be passing configuration information into the AB8500 Codec from Device Tree. The only reason we're still registering them using the MFD API is to overcome addressing issues encountered earlier. Each 'device' still belongs in the 'device' tree.
If we were to take this Device Tree and use it on something non-Linux, that OS will still need to know about each of the AB8500 devices and every associated configuration option. Only in Linux do we continue to register them though a different API, which doesn't affect any other OS.