Linux驱动之设备模型(5)

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本文深入探讨Linux驱动中的设备模型，详细解释了设备结构、设备属性及设备注册注销流程，通过实例解析展示了如何创建设备及其属性，并将其挂接到总线上。

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Linux驱动之设备模型(5)

(2013-02-21 11:11:20)

转载▼

标签：

设备模型

linux

分类：设备模型

原文地址： http://blog.youkuaiyun.com/hsly_support/article/details/7366595

6．设备

6.1 设备

l Linux设备模型中每一个设备用device结构来表示

struct device {

struct device *parent;

struct device_private *p;

struct kobject kobj;

const char *init_name;

const struct device_type *type;

struct bus_type *bus;

struct device_driver *driver;

void *platform_data;

dev_t devt;

struct klist_node knode_class;

struct class *class;

const struct attribute_group **groups;

void (*release)(structdevice *dev);

};

6.2 设备属性

l 设备属性由device_attribute来表示

struct device_attribute {

struct attribute attr;

ssize_t (*show)(struct device *dev,struct device_attribute *attr,

char *buf);

ssize_t (*store)(struct device *dev,struct device_attribute *attr,

const char *buf, size_t count);

};

DEVICE_ATTR(_name,_mode, _show, _store)

l 属性操作

n 添加属性

int device_create_file(struct device *device,

conststruct device_attribute *entry);

n 删除属性

void device_remove_file(struct device *dev,

const struct device_attribute*attr);

6.3 设备注册和注销

l 设备注册和注销

int device_register(struct device *dev);

void device_unregister(struct device *dev);

l 设备注册分析

注册函数由初始化设备(device_initialize)和添加设备到系统(device_add)中两步构成，主要分析一下第二步

n device_add，添加设备

int device_add(structdevice *dev)

{

struct device *parent = NULL;

struct class_interface *class_intf;

int error = -EINVAL;

dev = get_device(dev);

if (dev->init_name) {

dev_set_name(dev,"%s", dev->init_name);

dev->init_name = NULL;

}

parent = get_device(dev->parent);

setup_parent(dev, parent);

error = kobject_add(&dev->kobj,dev->kobj.parent, NULL);

error = device_create_file(dev,&uevent_attr);

if (MAJOR(dev->devt)) {

error = device_create_file(dev,&devt_attr);

}

error = device_add_class_symlinks(dev);

error = device_add_attrs(dev);

error = bus_add_device(dev);

kobject_uevent(&dev->kobj,KOBJ_ADD);

bus_probe_device(dev);

if (parent)

klist_add_tail(&dev->p->knode_parent,

&parent->p->klist_children);

if (dev->class) {

klist_add_tail(&dev->knode_class,

&dev->class->p->klist_devices);

list_for_each_entry(class_intf,

&dev->class->p->class_interfaces, node)

if(class_intf->add_dev)

class_intf->add_dev(dev,class_intf);

}

n bus_add_device

int bus_add_device(struct device *dev)

{

struct bus_type *bus =bus_get(dev->bus);

if (bus) {

error = device_add_attrs(bus,dev);

error =sysfs_create_link(&bus->p->devices_kset->kobj,

&dev->kobj,dev_name(dev));

error =sysfs_create_link(&dev->kobj,

&dev->bus->p->subsys.kobj,"subsystem");

klist_add_tail(&dev->p->knode_bus,&bus->p->klist_devices);

}

n bus_probe_device，为设备探测相应的驱动

bus_probe_device()->device_attach()

int device_attach(struct device *dev)

{

if (dev->driver) {

ret =device_bind_driver(dev);

} else {

ret = bus_for_each_drv(dev->bus, NULL, dev,__device_attach);

}

out_unlock:

device_unlock(dev);

return ret;

}

__device_attach()->driver_probe_device()->really_probe()->bus->probe()->drv->probe() 总线中定义的probe函数会优先执行，如果总线中没有定义probe才会执行驱动中定义的probe

6.4 实例解析

创建一个设备和它的属性version，并将此设备挂接到之前创建的总线上

#include

extern struct bus_type scbus_type;

extern struct device scbus;

static char *Version = "revision1.0";

void screlease(struct device *dev)

{

printk("scbusrelease\n");

}

struct device scdevice = {

.parent = &scbus,

.init_name = "scdevice0",

.bus = &scbus_type,

.release = screlease,

};

static ssize_t show_device_version(struct device *dev,

struct device_attribute *attr, char *buf)

{

return sprintf(buf, "%s\n", Version);

}

DEVICE_ATTR(version, 0ow_device_version, NULL);

static int __init scdevice_init(void)

{

int ret;

ret= device_register(&scdevice);

if(ret)

return ret;

ret= device_create_file(&scdevice, &dev_attr_version);

if(ret)

goto err_create;

printk("Createa scdevice");

return 0;

err_create:

device_unregister(&scdevice);

return ret;

}

static void __exit scdevice_exit(void)

{

device_remove_file(&scdevice,&dev_attr_version);

device_unregister(&scdevice);

printk("Removea scdevice");

}

module_init(scdevice_init);

module_exit(scdevice_exit);

MODULE_LICENSE("Dual BSD/GPL");

MODULE_AUTHOR("CJOK");

试验结果：