In this chapter, we will focus on an important hardware-related aspect of writing a device driver: how exactly to access and perform I/O (input/output, reads and writes) to hardware (or peripheral) I/O memory – the peripheral hardware chip that you are writing the driver for.

The motivation behind the knowledge you will gain in this chapter is straightforward: without this, how will you actually control the device? Most devices are driven by carefully calibrated writes and reads to their hardware registers and/or peripheral memory, also called hardware I/O memory. Linux, being a virtual memory-based OS, requires some abstraction in the way it works with peripheral I/O memory.

In this chapter, we will cover the following topics:

• Accessing hardware I/O memory from the kernel
• Understanding and using memory-mapped I/O
• Understanding...