Essential Linux Device Drivers

Several texts:

• Essential Linux Device Drivers (I really enjoyed this one. It has a strong introductory section on Linux and how device drivers generally work.)
• Linux Device Drivers (The "standard" with a free pdf link as mentioned by others)
• Understanding the Linux Kernel (The longer you spend here, the better you need to really understand the kernel. This will help.)

1. Linux Device Drivers - Jonathan Corbet, Alessandro Rubini, and Greg Kroah-Hartman
2. Essential Linux Device Drivers - Sreekrishnan Venkateswaran
3. Writing Linux Device Drivers - Jerry Cooperstein

I think a character device driver implementing mmap should be adequate. Linux Device Drives covers that in chapter 15.

Edit:

Well, i2c is a serial bus, so mmap is not an option. I will refer you to Essential Linux Device Drivers book. I believe it has a sample i2c EEPROM char device driver in Chapter 8. Hope this helps.