Yesterday I committed some more configs to generate doxygen documentation of FreeBSD-kernel drivers. I mechanically generated missing configs for subdirectories of src/sys/dev/. This means there is no dependency information included in the configs, and as such you will not get links e.g. to the PCI documentation, if a driver calls functions in the PCI driver (feel free to tell me about such dependencies).
If you want to generate the HTML or PDF version of some subsystem, just go to src/tools/kerneldoc/subsys/ an run “make” to get a list of targets to build. As an example, “make dev_sound” will generate the HTML version for the sound system, “make pdf-dev_sound” generates the PDF version. The sound system is probably the most “nice” example, as it includes a page with TODO items, and has even some real API docs instead of just the call-graphs and such automatically generated information.
Some drivers already have (some) doxygen markup (I did just a quick grep for „/*[*!]“ to detect doxygen markup indicators, no idea about the coverage or quality), namely:
There is more documentation than only for those drivers, I just listed those as there are at least parts of doxygen documentation inside.