I bought some books this winter I’d like to go through during the next weeks. Obviously, these are not the kind of book you read from the first page to the very last one. Linux Device Drivers (freely available on the net) has turned out to be useful as I was struggling to get a non-documented driver to work with my program. LDD is in fact really easy to use: you don’t need to have read all the other chapters to understand what you’re looking for.
See on amazon: