I'm not sure a common interface to all of these different channels makes sense, but surely a DSI library and an aux channel library would fit nicely alongside the existing DDC library.
DSI and the various other MIPI bits tend to be horribly panel and device specific. In one sense yes its a standard with standard commands, processes, queries etc, on the other a lot of stuff is oriented around the 'its a fixed configuration unit we don't need to have queries' view. There also tends to be a lot of vendor magic initialisation logic both chipset and device dependant, and often 'plumbing dependant' on SoC systems. This is doubly ugly with the I²C abstractions for DDC because SoC systems are not above putting the DDC on a standard I²C port being shared with other functionality.
Oh, I think you're also trying to get at how we expose some of these controls outside of the display driver -- right now, they're mostly exposed as properties on the output device. Things like backlight brightness, a million analog TV output values, dithering control and other more esoteric controls.
This is how the MIPI handling in the GMA500 driver works, although the existing code needs to be taken out and shot, which should be happening soon. There is a lot, like panel initialisation which is however not really going to fit a properties model.
Alan