Linux Kernel Architecture

Chapter 6: Device Drivers

Registering Devices

Registering devices consists of two separate steps as Figure 6-22 shows: Initializing the data structures of

the device, and including it into the data structure network.

device_register

device_initialize

device_add

Figure 6-22: Code flow diagram

fordevice_register.

device_initializemainly adds the new device to the device subsystem bykobj_set_kset_s(dev,

devices_subsys).

device_addrequires a little more effort. First of all, the parent/child relationship specified via

device->parentis brought over to the generic kernel object hierarchy:

drivers/base/core.c

int device_add(struct device *dev)

{

struct device *parent = NULL;

...

parent = get_device(dev->parent);

kobj_parent = get_device_parent(dev, parent);

dev->kobj.parent = kobj_parent;

...

Registering the device in the devices subsystem requires a simple call tokobject_addsince subsystem

membership was already set indevice_initialize.

drivers/base/core.c

kobject_set_name(&dev->kobj, "%s", dev->bus_id);

error = kobject_add(&dev->kobj);

...

Afterwardbus_add_deviceadds links within sysfs — one in the bus directory that points to the device,

and one in the device directory which points to the bus subsystem.bus_attach_devicetries to autoprobe

the device. If a suitable driver can be found, the device is added tobus->klist_devices.Thedeviceis

also added to the child list of the parent (before that, the device knew its parent, but the parent did not

know the child).

drivers/base/core.c

error = bus_add_device(dev);

bus_attach_device(dev);

if (parent)

klist_add_tail(&dev->knode_parent, &parent->klist_children);

...

}