Chapter 7: Understanding the Concept of Platform Devices and Drivers
The Linux kernel handles devices by using the concept of buses, that is, the links between the CPU and these devices. Some buses are smart enough and embed a discoverability logic to enumerate devices sitting on them. With such buses, early in the bootup phase, the Linux kernel requests these buses for the devices they have enumerated as well as the resources (such as interrupt lines and memory regions) they need to work correctly. PCI, USB, and SATA buses all come under this family of discoverable buses.
Unfortunately, the reality is not always so beautiful. There are a number of devices that the CPU is still unable to detect. Most of these non-discoverable devices are on-chip, although some of them sit on slow or dumb buses that do not support device discoverability.
As a result, the kernel must provide mechanisms for receiving information about the hardware and users must inform the kernel where these devices...
