Linux Device Drivers by O'Reilly is a very good comprehensive book on the subject. I found it very helpful in every area of writing a device driver for Linux. It is written with the understanding that the reader has had some device driver programming experience, it is not a book for beginners. The only area I felt was lacking was in the number of examples of actual C code. The examples that are given are very good, there just isn't enough of them. I was able to get some code examples from the internet which helped me finish the driver I was working on.