Chapter 6. The PCI Layer and Network Interface Cards

Given the popularity of the PCI bus, on the x86 as well as other architectures, we will spend a few pages on it so that you can understand how PCI devices are managed by the kernel, with special emphasis on network devices. This chapter will help you find a context for the code about device registration we will see in Chapter 8. You will also learn a bit about how PCI handles some nifty kernel features such as probing and power management. For an in-depth discussion of PCI, such as device driver design, PCI bus features, and implementation details, refer to Linux Device Drivers and Understanding the Linux Kernel, as well as PCI specifications.

The PCI subsystem (also known as the PCI layer ) in the kernel provides all the generic functions that are used in common by various PCI device drivers. This subsystem takes a lot of work off the shoulders of the programmer for each individual device, lets drivers be written in a clean manner, and makes it easier for the kernel to collect and maintain information about the devices, such as accounting information and statistics.

In this chapter, we will see the meaning of a few key data structures used by the PCI layer and how these structures are initialized by one common NIC device driver. I'll conclude with a few words on the PCI power management and Wake-on-LAN features.