Introducing device trees
If you are working with Arm or PowerPC SoCs, you are almost certainly going to encounter device trees at some point. This section aims to give you a quick overview of what they are and how they work. We will revisit the topic of device trees repeatedly throughout the course of this book.
A device tree is a flexible way of defining the hardware components of a computer system. Bear in mind that a device tree is just static data, not executable code. Usually, the device tree is loaded by the bootloader and passed to the kernel, although it is possible to bundle the device tree with the kernel image itself to cater for bootloaders that are not capable of loading them separately.
The format is derived from a Sun Microsystems bootloader known as OpenBoot, which was formalized as the Open Firmware specification, which is IEEE standard IEEE1275-1994. It was used in PowerPC-based Macintosh computers and so was a logical choice for the PowerPC Linux port. Since...
