总线设备驱动模型----驱动篇

如果你了解了前面总线、设备模型，分析总线设备驱动模型的driver相对来说会轻松很多。开始也是看看其数据结构。 点击(此处)折叠或打开
struct device_driver {

const char *name; //驱动的名字

struct bus_type *bus; //驱动呈现属于的总线类型

struct module *owner;

const char *mod_name; /* used for built-in modules */

bool suppress_bind_attrs; /* disables bind/unbind via sysfs */

const struct of_device_id *of_match_table;

int (*probe) (struct device *dev);
//驱动挂载的时候调用

int (*remove) (struct device *dev);
//卸载的时候调用

void (*shutdown) (struct device *dev);

int (*suspend) (struct device *dev, pm_message_t state);

int (*resume) (struct device *dev);

const struct attribute_group **groups;

const struct dev_pm_ops *pm;

struct driver_private *p;

};
与device类型相似，其中有一个指向driver_private的指针p，一些与其他的组件相关的联系都被移到这个结构变量中。 点击(此处)折叠或打开
struct driver_private {

struct kobject kobj; //在sysfs中代表目录本身

struct klist klist_devices;//驱动链表

struct klist_node knode_bus; //挂载在总线的驱动链表的节点

struct module_kobject *mkobj;//driver与相关的module之间的联系

struct device_driver *driver;

};

#define to_driver(obj) container_of(obj, struct driver_private, kobj)
由上面可以看出driver指针最后也有driver_private回到了device_driver之中，下面也来看看驱动的属性文件的表示方法 点击(此处)折叠或打开
struct driver_attribute {

struct attribute attr;

ssize_t (*show)(struct device_driver *driver, char *buf);

ssize_t (*store)(struct device_driver *driver, const char *buf,

size_t count);

};

#define DRIVER_ATTR(_name, _mode, _show, _store) \

struct driver_attribute driver_attr_##_name = \

__ATTR(_name, _mode, _show, _store)
上面只是有两个读写函数，看完了关于驱动的一些重要的数据结构，那么开始重要的，如何向内核注册一个drv呢？我们使用driver_register 点击(此处)折叠或打开
int driver_register(struct device_driver *drv)

{

int ret;

struct device_driver *other;

BUG_ON(!drv->bus->p);

if ((drv->bus->probe && drv->probe) ||

(drv->bus->remove && drv->remove) ||

(drv->bus->shutdown && drv->shutdown))

printk(KERN_WARNING "Driver '%s' needs updating - please use "

"bus_type methods\n", drv->name);

other = driver_find(drv->name, drv->bus);

if (other) {

put_driver(other);

printk(KERN_ERR "Error: Driver '%s' is already registered, "

"aborting...\n", drv->name);

return -EBUSY;

}

ret = bus_add_driver(drv);

if (ret)

return ret;

ret = driver_add_groups(drv, drv->groups);

if (ret)

bus_remove_driver(drv);

return ret;

}
从函数可以看出，首先drv->bus一定要预先设置。在使用driver_find从bus的驱动链表中特定名字的driver，那么就进入这个函数的重点的东西bus_add_driver，几乎注册所有的工作都是由它来完成。
点击(此处)折叠或打开
int bus_add_driver(struct device_driver *drv)

{

struct bus_type *bus;

struct driver_private *priv;

int error = 0;

bus = bus_get(drv->bus);//增加对bus的引用

if (!bus)

return -EINVAL;

pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);

priv = kzalloc(sizeof(*priv), GFP_KERNEL);//分配初始化一个drv->p，也就是上面的driver_private结构

if (!priv) {

error = -ENOMEM;

goto out_put_bus;

}

klist_init(&priv->klist_devices, NULL, NULL);

priv->driver = drv;

drv->p = priv;

priv->kobj.kset = bus->p->drivers_kset;

error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,

"%s", drv->name);//将drv加入sysfs

if (error)

goto out_unregister;

if (drv->bus->p->drivers_autoprobe) {

error = driver_attach(drv);//如果总线可以自动的probe，就会调用匹配函数

if (error)

goto out_unregister;

}

klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);//将drv挂入到总线的链表中

module_add_driver(drv->owner, drv);//创建driver相关的模块

error = driver_create_file(drv, &driver_attr_uevent);//在drv目录下创建event属性文件

if (error) {

printk(KERN_ERR "%s: uevent attr (%s) failed\n",

__func__, drv->name);

}

error = driver_add_attrs(bus, drv);//添加属性

if (error) {

/* How the hell do we get out of this pickle? Give up */

printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",

__func__, drv->name);

}

if (!drv->suppress_bind_attrs) {

error = add_bind_files(drv);

if (error) {

/* Ditto */

printk(KERN_ERR "%s: add_bind_files(%s) failed\n",

__func__, drv->name);

}

}

kobject_uevent(&priv->kobj, KOBJ_ADD);//向用户空间发布kobj_add消息

return 0;

out_unregister:

kobject_put(&priv->kobj);

kfree(drv->p);

drv->p = NULL;

out_put_bus:

bus_put(bus);

return error;

}
其实上面的处理过程相对于设备来说，会简单很多，下面主要对当驱动挂接的时候，怎么去匹配进行分析。 点击(此处)折叠或打开
int driver_attach(struct device_driver *drv)

{

return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);

}
点击(此处)折叠或打开
static int __driver_attach(struct device *dev, void *data)

{

struct device_driver *drv = data;

/*

* Lock device and try to bind to it. We drop the error

* here and always return 0, because we need to keep trying

* to bind to devices and some drivers will return an error

* simply if it didn't support the device.

*

* driver_probe_device() will spit a warning if there

* is an error.

*/

if (!driver_match_device(drv, dev))

return 0;

if (dev->parent) /* Needed for USB */

device_lock(dev->parent);

device_lock(dev);

if (!dev->driver)

driver_probe_device(drv, dev);

device_unlock(dev);

if (dev->parent)

device_unlock(dev->parent);

return 0;
点击(此处)折叠或打开
static inline int driver_match_device(struct device_driver *drv,

struct device *dev)

{

return drv->bus->match ? drv->bus->match(dev, drv) : 1;

}
最终也是调用总线的match函数来完成设备与驱动的匹配的过程。以上分析了总线、设备、驱动三种类型，主要是在注册上，其主要是在sysfs中创建目录和属性文件。在设备或者驱动注册到总线上，总线是如何为其找到对应的驱动的过程，下面一个图能很好的说明这一过程。

由图可以清楚的看出，bus的作用是向内核注册一条总线，并将drv一一加入到总线的drv链表，dev一一加入到总线的dev链表。当有设备或驱动注册的时候，在驱动或者设备链表一一取出，调用总线的match函数来完成匹配，匹配成功后调用总线的probe函数。回顾下driver_register的作用，首先会将drv放入到bus得drv链表，从bus的dev链表取出每一个dev，用总线的match函数来判断能否支持drvdevice_register的作用和driver一样，将dev放入到bus得dev链表，从bus的drv链表取出每一个drv，用总线的match函数来判断能否支持dev。 点击(此处)折叠或打开
extern struct bus_type my_bus_type;

static int my_probe(struct device *dev)

{

printk("Driver found device which my driver can handle!\n");

return 0;

}

static int my_remove(struct device *dev)

{

printk("Driver found device unpluged!\n");

return 0;

}

struct device_driver my_driver = {

.name = "my_dev",

.bus = &my_bus_type,

.probe = my_probe,

.remove = my_remove,

};

/*

* Export a simple attribute.

*/

static ssize_t mydriver_show(struct device_driver *driver, char *buf)

{

return sprintf(buf, "%s\n", "This is my driver!");

}

static DRIVER_ATTR(drv, S_IRUGO, mydriver_show, NULL);

static int __init my_driver_init(void)

{

int ret = 0;

/*注册驱动*/

driver_register(&my_driver);

/*创建属性文件*/

driver_create_file(&my_driver, &driver_attr_drv);

return ret;

}

static void my_driver_exit(void)

{

driver_unregister(&my_driver);

}

module_init(my_driver_init);

module_exit(my_driver_exit);

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