总线设备驱动模型——驱动篇

驱动struct device_driver

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;   /* usedfor 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;

};

struct driver_private

    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。由driver_private可以看出driver指针最后也由driver_private回到了device_driver之中。

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)

驱动属性struct driver_attribute

    下面来看看驱动的属性文件的表示方法，这里只是有两个读写函数。

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)

驱动注册driver_register()

    看完了关于驱动的一些重要的数据结构，那么如何向内核注册一个drv呢？使用driver_register，首先drv->bus一定要预先设置，再使用driver_find从bus的驱动链表中特定名字的driver，然后就进入这个函数的重点bus_add_driver，几乎注册所有的工作都是由它来完成。

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;

}

    几乎注册所有的工作都是由bus_add_driver来完成。

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': adddriver %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: ueventattr (%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 thispickle? 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。

int driver_attach(struct device_driver *drv)

{

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

}

 

static int __driver_attach(struct device *dev, void *data)

{

    struct device_driver *drv = data;

 

    /*

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

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

     * to bind to devices and somedrivers will return an error

     * simply if it didn't supportthe device.

     *

     * driver_probe_device() willspit 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;

}

    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。

static inline int driver_match_device(struct device_driver *drv,

                 struct device *dev)

{

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

}

module_init(my_driver_init)

extern struct bus_type my_bus_type;

 

static int my_probe(struct device *dev)

{

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

    return 0;

}

 

static int my_remove(struct device *dev)

{

    printk("Driver founddevice unpluged!\n");

    return 0;

}

 

struct device_drivermy_driver = {

    .name = "my_dev",

    .bus = &my_bus_type,

    .probe = my_probe,

        .remove    = my_remove,

};

 

/*

 * Export a simple attribute.

 */

static ssize_tmydriver_show(struct device_driver *driver, char *buf)

{

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

}

 

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

 

static int __initmy_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);