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分类: 嵌入式

2012-09-22 17:08:25

内核的开发者将总线,设备,驱动这三者用软件思想抽象了出来,巧妙的建立了其间的关系,使之更形象化。结合前面所学的知识,总的来说其三者间的关系为bus有两条链表,分别用于挂接设备和驱动,指定了其自身bus的device或者driver最后都会分别连接到对应bus的这两条链表上,而总线又有其始端,为bus_kset,一个driver可以对应于几个设备,因此driver同样有其设备链表,用于挂接可以操作的设备,其自身也有bus挂接点,用于将自身挂接到对应bus(每个driver只属于一条总线),而对于device,一个设备只属于一条总线,只能有一个driver与其对应,因此对于device,都是单一的,一个driver挂接点,一个bus挂接点,device与bus相同的是都有始端,device为devices_kset,因此device的注册同时会出现在对应的bus目录和device总目录下。好了,下面就以源码为例分别分析一下bus,device,driver的注册过程。
一、bus的注册
      bus的注册比较简单,首先来看一下bus的结构:
     
[cpp]
struct bus_type {  
    const char      *name;                //名字   
    struct bus_attribute    *bus_attrs;           //bus属性集   
    struct device_attribute *dev_attrs;           //device属性集   
    struct driver_attribute *drv_attrs;           //driver属性集   
    int (*match)(struct device *dev, struct device_driver *drv);  
    int (*uevent)(struct device *dev, struct kobj_uevent_env *env);  
    int (*probe)(struct device *dev);  
    int (*remove)(struct device *dev);  
    void (*shutdown)(struct device *dev);  
    int (*suspend)(struct device *dev, pm_message_t state);  
    int (*resume)(struct device *dev);  
    const struct dev_pm_ops *pm;  
    struct bus_type_private *p;                   //bus的私有成员   
};  
//其中重点看一下私有成员结构体:   
struct bus_type_private {  
    struct kset subsys;                           //bus内嵌的kset,代表其自身   
    struct kset *drivers_kset;                      
    struct kset *devices_kset;  
    struct klist klist_devices;                   //包含devices链表及其操作函数   
    struct klist klist_drivers;                   //driver链表及其操作函数   
    struct blocking_notifier_head bus_notifier;  
    unsigned int drivers_autoprobe:1;              //匹配成功自动初始化标志   
    struct bus_type *bus;                            
}; 
  无论是bus,driver,还是device其本身特征都放在私有成员里,其注册时,都会申请并填充这个结构体,下面具体分析一下bus的注册流程,从bus_register开始:
     
[cpp]
int bus_register(struct bus_type *bus)  
{  
    int retval;  
    struct bus_type_private *priv;  
    priv = kzalloc(sizeof(struct bus_type_private), GFP_KERNEL);    //进入时bus_type->bus_type_private为NULL   
    if (!priv)                                                      //该函数主要是对其的设置   
        return -ENOMEM;  
    priv->bus = bus;                                                //私有成员的bus回指该bus   
    bus->p = priv;                                                  //初始化bus->p,即其私有属性   
    BLOCKING_INIT_NOTIFIER_HEAD(&priv->bus_notifier);  
    retval = kobject_set_name(&priv->subsys.kobj, "%s", bus->name);  //设置该bus的名字,bus是kset的封装   
    if (retval)  
        goto out;  
                                                      //bus_kset即为所有bus的总起始端点   
                                                      //围绕bus内嵌的kset初始化,和kset的初始化时围绕   
    priv->subsys.kobj.kset = bus_kset;                //kobj相似,没有parent时,就会用kset的kobj,此处即是   
    priv->subsys.kobj.ktype = &bus_ktype;                    //属性操作级别统一为bus_ktype   
    priv->drivers_autoprobe = 1;                                    //设置该标志,当有driver注册时,会自动匹配devices   
                                                                    //上的设备并用probe初始化,   
                                                                    //当有device注册时也同样找到  driver并会初始化   
    retval = kset_register(&priv->subsys);                          //注册kset,创建目录结构,以及层次关系   
    if (retval)  
        goto out;  
    retval = bus_create_file(bus, &bus_attr_uevent);                //当前bus目录下生成bus_attr_uevent属性文件   
    if (retval)  
        goto bus_uevent_fail;  
    priv->devices_kset = kset_create_and_add("devices", NULL,       //初始化bus目录下的devices目录,里面级联了该bus下设备,   
                         &priv->subsys.kobj);                    //仍然以kset为原型   
    if (!priv->devices_kset) {  
        retval = -ENOMEM;  
        goto bus_devices_fail;  
    }  
    priv->drivers_kset = kset_create_and_add("drivers", NULL,       //初始化bus目录下的drivers目录,里面级联了该bus下设备的driver   
                         &priv->subsys.kobj);  
    if (!priv->drivers_kset) {  
        retval = -ENOMEM;  
        goto bus_drivers_fail;  
    }  
    klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);  //初始化klist_devices里的操作函数成员   
    klist_init(&priv->klist_drivers, NULL, NULL);                            //klist_drivers里的操作函数置空   
    retval = add_probe_files(bus);                                           //增加bus_attr_drivers_probe和bus_attr_drivers_autoprobe   
    if (retval)                                                              //属性文件   
        goto bus_probe_files_fail;  
    retval = bus_add_attrs(bus);                                             //增加默认的属性文件   
    if (retval)  
        goto bus_attrs_fail;  
    pr_debug("bus: '%s': registered/n", bus->name);  
    return 0;  
bus_attrs_fail:                                                               //以下为错误处理   
    remove_probe_files(bus);  
bus_probe_files_fail:  
    kset_unregister(bus->p->drivers_kset);  
bus_drivers_fail:  
    kset_unregister(bus->p->devices_kset);  
bus_devices_fail:  
    bus_remove_file(bus, &bus_attr_uevent);  
bus_uevent_fail:  
    kset_unregister(&bus->p->subsys);  
out:  
    kfree(bus->p);  
    bus->p = NULL;  
    return retval;  
   由此可见,bus又是kset的封装,bus_register主要完成了其私有成员bus_type_private的初始化,并初始化了其下的两个目录devices和drivers,及其属性文件,bus有个自己的根目录也就是bus有个起始端点,是bus_kset,经过此番的注册,bus目录下将会出现我们注册的bus,并且其下会有device和driver两个子目录,代表它下面的driver和device链表。
二、driver的注册
  下面看一下driver是怎么和bus关联起来的,首先看下driver的结构:
    
[cpp]
struct device_driver {  
    const char      *name;            //名字   
    struct bus_type     *bus;        //其所在的bus   
    struct module       *owner;  
    const char      *mod_name;  /* used for built-in modules */  
    bool suppress_bind_attrs;   /* disables bind/unbind via sysfs */  
#if defined(CONFIG_OF)   
    const struct of_device_id   *of_match_table;  
#endif   
    int (*probe) (struct device *dev);        //匹配成功时可能会调用到的函数   
    int (*remove) (struct device *dev);  
    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;                 //私有成员,表示driver   
};  
//重点看下driver的私有成员   
struct driver_private {  
    struct kobject kobj;                      //代表driver自身   
    struct klist klist_devices;               //可以操控的设备链表   
    struct klist_node knode_bus;              //挂接到bus的节点   
    struct module_kobject *mkobj;             //模块相关   
    struct device_driver *driver;             //回指该driver   
}; 
  如同bus一样,重点的仍是可以代表其自身的私有属性,下面具体看一下driver的注册过程,从driver_register开始:
    
[cpp]
int driver_register(struct device_driver *drv)  
{  
    int ret;  
    struct device_driver *other;  
    BUG_ON(!drv->bus->p);  
    if ((drv->bus->probe && drv->probe) ||           //driver和bus的同名操作函数如果同时存在,会出现警告   
        (drv->bus->remove && drv->remove) ||         //并且会优先选用bus的   
        (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);        //进入bus的driver链表,确认该driver是否已经注册   
    if (other) {  
        put_driver(other);                            //找到了再减少引用计数,并且报错退出   
        printk(KERN_ERR "Error: Driver '%s' is already registered, "  
            "aborting.../n", drv->name);  
        return -EBUSY;  
    }  
    ret = bus_add_driver(drv);                       //如果没有注册,那么把该driver加入所在bus   
    if (ret)  
        return ret;  
    ret = driver_add_groups(drv, drv->groups);  
    if (ret)  
        bus_remove_driver(drv);  
    return ret;  
}  
/**************************************************** 
× 跟踪一下driver_find(drv->name, drv->bus) 
****************************************************/  
struct device_driver *driver_find(const char *name, struct bus_type *bus)  
{  
    struct kobject *k = kset_find_obj(bus->p->drivers_kset, name);  //bus->p->drivers_kset代表bus下   
    struct driver_private *priv;                                    //的driver目录,此处会遍历bus的       
                                                                    //driver链表,通过driver内嵌的   
    if (k) {                                                        //kobj名字比较   
        priv = to_driver(k);  
        return priv->driver;                                 //如果找到同名的kobj那么返回该driver   
    }  
    return NULL;  
}  
//看一下kset_find_obj吧:   
struct kobject *kset_find_obj(struct kset *kset, const char *name)  
{  
    struct kobject *k;  
    struct kobject *ret = NULL;  
    spin_lock(&kset->list_lock);  
    list_for_each_entry(k, &kset->list, entry) {                   //遍历bus下的driver链表,如果   
        if (kobject_name(k) && !strcmp(kobject_name(k), name)) {   //找到那么返回找到的kobj,并且把   
            ret = kobject_get(k);                                  //该driver的kobj引用计数+1   
            break;  
        }  
    }  
    spin_unlock(&kset->list_lock);  
    return ret;  
}  
/************************************************ 
× 再来跟踪一下driver_register里面的另外一个函数 
× bus_add_driver(drv) 
************************************************/  
int bus_add_driver(struct device_driver *drv)   
{  
    struct bus_type *bus;  
    struct driver_private *priv;  
    int error = 0;  
    bus = bus_get(drv->bus);                                        //取得其所在bus的指针   
    if (!bus)  
        return -EINVAL;  
    pr_debug("bus: '%s': add driver %s/n", bus->name, drv->name);   //开始初始化这个driver的私有成员,   
                                                                    //和bus类似   
    priv = kzalloc(sizeof(*priv), GFP_KERNEL);  
    if (!priv) {  
        error = -ENOMEM;  
        goto out_put_bus;  
    }  
    klist_init(&priv->klist_devices, NULL, NULL);                   //设备操作函数清空,设备链表初始化   
    priv->driver = drv;                                               
    drv->p = priv;  
    priv->kobj.kset = bus->p->drivers_kset;                          //kset指定到bus下面   
    error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,   //建立层次结构和属性文件   
                     "%s", drv->name);  
    if (error)  
        goto out_unregister;  
    if (drv->bus->p->drivers_autoprobe) {                            //bus的自动匹配如果设置为真,   
        error = driver_attach(drv);                                  //那么到bus的devices上去匹配设备   
        if (error)  
            goto out_unregister;  
    }  
    klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);        //把driver挂接到bus的driver链表   
    module_add_driver(drv->owner, drv);  
    error = driver_create_file(drv, &driver_attr_uevent);            //以下添加该driver相关属性文件   
    if (error) {  
        printk(KERN_ERR "%s: uevent attr (%s) failed/n",  
            __func__, drv->name);  
    }  
    error = driver_add_attrs(bus, drv);  
    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);  
    return 0;  
out_unregister:  
    kobject_put(&priv->kobj);  
    kfree(drv->p);  
    drv->p = NULL;  
out_put_bus:  
    bus_put(bus);  
    return error;  
}  
/**************************************************************** 
× 接下来就剩下最终要的匹配函数driver_attach(drv)了,我们来看一下: 
****************************************************************/  
int driver_attach(struct device_driver *drv)                            //遍历bus的设备链表找到   
{                                                                       //合适的设备就调用__driver_attach,   
    return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);      //NULL表示从头开始遍历   
}    
//============   
int bus_for_each_dev(struct bus_type *bus, struct device *start,  
             void *data, int (*fn)(struct device *, void *))  
{  
    struct klist_iter i;  
    struct device *dev;  
    int error = 0;  
    if (!bus)  
        return -EINVAL;  
    klist_iter_init_node(&bus->p->klist_devices, &i,              //进入bus的devices链表   
                 (start ? &start->p->knode_bus : NULL));  
    while ((dev = next_device(&i)) && !error)                     //设备存在则调用fn即__driver_attach   
        error = fn(dev, data);                                    //进行匹配   
    klist_iter_exit(&i);  
    return error;  
}   
/********************************************* 
× 接着看一下__driver_attach这个函数 
*********************************************/  
static int __driver_attach(struct device *dev, void *data)  
{  
    struct device_driver *drv = data;  
    if (!driver_match_device(drv, dev))                //进行匹配   
        return 0;  
    if (dev->parent) /* Needed for USB */  
        device_lock(dev->parent);  
    device_lock(dev);  
    if (!dev->driver)                               //如果设备没有指定driver   
        driver_probe_device(drv, dev);              //那么需要初始化匹配到的这个设备   
    device_unlock(dev);  
    if (dev->parent)  
        device_unlock(dev->parent);  
    return 0;  
}  
/********************************************* 
× 又遇到两个分支,囧,先看一下driver_match_device  
*********************************************/   
static inline int driver_match_device(struct device_driver *drv,      //bus的match存在就用bus的   
                                      struct device *dev)             //,否则就直接匹配成功...   
{                                                                     //match通常实现为首先扫描   
    return drv->bus->match ? drv->bus->match(dev, drv) : 1;           //driver支持的id设备表,如果   
}                                                                     //为NULL就用名字进行匹配   
/************************************ 
× 再来看一下driver_probe_device这个函数  
************************************/   
int driver_probe_device(struct device_driver *drv, struct device *dev)  
{  
    int ret = 0;  
    if (!device_is_registered(dev))                              //判断该设备是否已经注册   
        return -ENODEV;  
    pr_debug("bus: '%s': %s: matched device %s with driver %s/n",  
         drv->bus->name, __func__, dev_name(dev), drv->name);  
    pm_runtime_get_noresume(dev);  
    pm_runtime_barrier(dev);  
    ret = really_probe(dev, drv);                               //调用really_probe   
    pm_runtime_put_sync(dev);  
    return ret;  
}  
/************************************ 
× 看一下device_is_registered 
************************************/  
static inline int device_is_registered(struct device *dev)  
{  
    return dev->kobj.state_in_sysfs;                           //在sysfs中表示已经注册   
}  
/************************************ 
× 再看really_probe 
************************************/  
static int really_probe(struct device *dev, struct device_driver *drv)  
{  
    int ret = 0;  
    atomic_inc(&probe_count);  
    pr_debug("bus: '%s': %s: probing driver %s with device %s/n",  
         drv->bus->name, __func__, drv->name, dev_name(dev));  
    WARN_ON(!list_empty(&dev->devres_head));  
    dev->driver = drv;                                     //device的driver初始化成该driver   
    if (driver_sysfs_add(dev)) {                        
                 printk(KERN_ERR "%s: driver_sysfs_add(%s) failed/n",  
            __func__, dev_name(dev));  
        goto probe_failed;  
    }  
                                                         //利用probe初始化设备   
    if (dev->bus->probe) {                               //如果bus的probe存在就用bus的,   
        ret = dev->bus->probe(dev);                      //如果bus的不存在driver的存在   
        if (ret)                                         //再用driver的   
            goto probe_failed;  
    } else if (drv->probe) {  
        ret = drv->probe(dev);  
        if (ret)  
            goto probe_failed;  
    }  
    driver_bound(dev);                              //调用driver_bound进行绑定   
    ret = 1;  
    pr_debug("bus: '%s': %s: bound device %s to driver %s/n",  
         drv->bus->name, __func__, dev_name(dev), drv->name);  
    goto done;  
probe_failed:  
    devres_release_all(dev);  
    driver_sysfs_remove(dev);  
    dev->driver = NULL;  
    if (ret != -ENODEV && ret != -ENXIO) {  
        /* driver matched but the probe failed */  
        printk(KERN_WARNING  
               "%s: probe of %s failed with error %d/n",  
               drv->name, dev_name(dev), ret);  
    }  
    /* 
     * Ignore errors returned by ->probe so that the next driver can try 
     * its luck. 
     */  
    ret = 0;  
done:  
    atomic_dec(&probe_count);  
    wake_up(&probe_waitqueue);  
    return ret;  
}  
/********************************** 
* 最后跟一下driver_bound(dev)这个函数 
**********************************/  
static void driver_bound(struct device *dev)  
{  
    if (klist_node_attached(&dev->p->knode_driver)) {                   //判断是否已经绑定   
        printk(KERN_WARNING "%s: device %s already bound/n",  
            __func__, kobject_name(&dev->kobj));  
        return;  
    }  
    pr_debug("driver: '%s': %s: bound to device '%s'/n", dev_name(dev),  
         __func__, dev->driver->name);  
    klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);  //将设备添加   
                                                                            //到driver的链表   
    if (dev->bus)  
        blocking_notifier_call_chain(&dev->bus->p->bus_notifier,  
                         BUS_NOTIFY_BOUND_DRIVER, dev);  
}  
//all end 
  总结一下,driver的注册,主要涉及将自身挂接到bus的driver链表,并将匹配到的设备加入自己的device链表,并且将匹配到的device的driver成员初始化为该driver,私有属性的driver节点也挂到driver的设备链表下,其中匹配函数是利用利用bus的match函数,该函数通常判断如果driver有id表,就查表匹配,如果没有就用driver和device名字匹配。当匹配成功后如果自动初始化标志允许则调用初始化函数probe,bus的probe优先级始终高于driver的。另外注意一点driver是没有总的起始端点的,driver不是可具体描述的事物。
   由于篇幅比较长,device的分析放到下一篇《linux设备模型之bus,device,driver分析<二>》   ^_^!
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