SCOPE OF SYMBOLS
It is important to carefully consider the scope of symbols in the kernel. The default is to make everything static, unless some reason requires the opposite.
There are several reasons for this policy, the main one is that the kernel is one monolithic name-space, and pollution is not a good idea here either.
For device drivers and other modules that do not add new internal interfaces to the kernel, the entire source should be in one file if possible. That way all symbols can be made static.
If for some reason a module is split over multiple source files, then try to split the module along some major fault-line and consider using the number of global symbols as your guide. The fewer the better.