I'm trying to properly bus-space the Brooktree848 driver from FreeBSD,
both to have a clean interface in FreeBSD and in the hope that NetBSD,
OpenBSD and FreeBSD can share the driver without any significant
differences.

However, the Bt848 include its own i2c bus, accessed through a port (a
couple of the registers on the chip control all the access; addressing
etc has to be addressed through this).  I'd like to export this as its
own bus space, as it fit the bus space API perfectly.  There are a
couple of 'sub-drivers' that will access this space - including the
tuner drivers and the MSP drivers (for NICAM sound etc).

As far as I'm able to tell, this is not possible to do using the
present bus spaces, as a driver cannot introduce a new tag and have
callbacks for the bus_space_write_X functions etc.

Is there any idom for handling situations like this?

Eivind.