Linux Kernel Architecture

Chapter 6: Device Drivers

Data Structures

The kernel provides several data structures to manage the system’s PCI structures. They are declared in

<pci.h>and are interlinked by a network of pointers. I give an overview of the structure elements below

before moving on to take a closer look at their definitions.

❑ The individual buses in the system are represented by instances ofpci_bus.

❑ Thepci_devstructure is provided for individual devices, cards, and function units.

❑ Each driver is described by an instance ofpci_driver.

The kernel makes two globallist_heads available to head the network of PCI data structures (both are

defined in<pci.h>).

❑ pci_root_buseslists all the PCI buses in the system. It is the starting point when the data struc-

tures are scanned ‘‘downward‘‘ to find all devices attached to the individual buses.

❑ pci_deviceslinks all PCI devices in the system without taking the bus structure into account.

This is useful when a driver wants to search for all devices it supports because the topology is of

no interest in this situation (it is, of course, possible to find the bus associated with a device using

the many links between the PCI data structures, as you will see below).

Representation of Buses

Each PCI bus is represented in memory by an instance of thepci_busdata structure, which is defined as

follows:

<pci.h>

#define PCI_BUS_NUM_RESOURCES 8

struct pci_bus {

struct list_head node; /* node in list of buses */

struct pci_bus *parent; /* parent bus this bridge is on */

struct list_head children; /* list of child buses */

struct list_head devices; /* list of devices on this bus */

struct pci_dev *self; /* bridge device as seen by parent */

struct resource *resource[PCI_BUS_NUM_RESOURCES];

/* address space routed to this bus */

struct pci_ops *ops; /* configuration access functions */

void *sysdata; /* hook for sys-specific extension */

struct proc_dir_entry *procdir; /* directory entry in /proc/bus/pci */

unsigned char number; /* bus number */

unsigned char primary; /* number of primary bridge */

unsigned char secondary; /* number of secondary bridge */

unsigned char subordinate; /* max number of subordinate buses */

char name[48];

...

};

The structure is divided into function sections as indicated by the source code formatting.