Representing and addressing devices

In the device tree, a node is the representational unit of a device. In other words, a device is represented by at least one node. Following this, device nodes can either be populated with other nodes (therefore, creating a parent-child relationship) or with properties (which would describe the device corresponding to the node they populate).

While each device can operate standalone, there are situations where a device might want to be accessed by its parent or where a parent might want to access one of its children. For example, such situations occur when a bus controller (the parent node) wants to access one or more of the devices (declared as a sub-node) sitting on its bus. Typical examples include I2C controllers and I2C devices, SPI controllers and SPI devices, CPUs and memory-mapped devices, and more. Thus, the concept of device addressing has emerged. Device addressing has been introduced with a reg property, which is used in each addressable...