Correct way to build in-tree module?

[Matt Ventura <mattventura@Me.com>]

Hi,

I'd like to build a module that is in-tree, but not enabled by the 
Debian kernel by default (module 'pmbus', selected by CONFIG_PMBUS). I 
would rather not build an entire custom kernel just for one module.

Most of the resources out there are for building *out of tree* modules, 
but this is in-tree. Or, they tell you how to do a one-time build of the 
module, but not how to get it into DKMS or anything that would keep the 
module up to date as you install new kernel versions. The module is not 
listed in module-assistant either.

So, what is the right (or at least, best) way to do this, that won't 
break on a kernel update?

Thanks,

Matt