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。

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。

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

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

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。

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。

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 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;

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drv

device_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。

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);