设备模型、设备与驱动关联的全过程分析 platform_device platform_driver driver bus关系

 

 

1.     平台驱动注册过程    具体的目录如下：关于设备模型、设备与驱动关联的全过程分析。... 11.1 at91_i2c_init()函数... 11.2 platform_driver_register()函数... 21.3     driver_register()函数... 41.4 bus_add_driver()函数... 51.5 dd.c文件driver_attach()函数... 71.1 at91_i2c_init()函数在文件drivers/i2c/busses/i2c-at91.c中，定义了结构体struct platform_driver并进行了初始化，

通过使用module_init()宏进行声明，当模块被加载到内核时会调用 at91_i2c_init()函数。在此函数中，

调用了platform_driver_register()函数来完成注册。static struct platform_driver at91_i2c_driver = {.probe= at91_i2c_probe,.remove = __devexit_p(at91_i2c_remove),.suspend= at91_i2c_suspend,.resume= at91_i2c_resume,.driver= {.name= "at91_i2c",.owner= THIS_MODULE,},};static int __init at91_i2c_init(void){     return platform_driver_register(&at91_i2c_driver);}1.2 platform_driver_register()函数在文件drivers/base/platform.c中，实现并导出了platform_driver_register()函数，以便使其他模块中

的函数可以调用此函数。它在完成简单的包装后，调用了driver_register()函数，完成了从平台实现到Linux内核实现的过渡。int platform_driver_register(struct platform_driver *drv) {    /*设置成platform_bus_type这个很重要，因为driver和device是通过bus联系在一起的，具体在本例中是通过  

platform_bus_type中注册的回调例程和属性来是实现的， driver与device的匹配就是通过 

platform_bus_type注册的回到例程platform_match ()来完成的。*/drv->driver.bus = &platform_bus_type; //在really_probe函数中，回调了platform_drv_probe函数if (drv->probe) drv->driver.probe = platform_drv_probe; if (drv->remove) drv->driver.remove = platform_drv_remove; if (drv->shutdown) drv->driver.shutdown = platform_drv_shutdown; if (drv->suspend) drv->driver.suspend = platform_drv_suspend; if (drv->resume) drv->driver.resume = platform_drv_resume; return driver_register(&drv->driver); } EXPORT_SYMBOL_GPL(platform_driver_register); 在platform_driver_register()函数中，对总线附值使用了如下语句，给总线类型和相关操作函数赋值。

drv->driver.bus = &platform_bus_type; struct bus_type platform_bus_type = {    .name       = "platform",    .dev_attrs  = platform_dev_attrs,    .match      = platform_match,    .uevent     = platform_uevent,    .suspend    = platform_suspend,    .suspend_late   = platform_suspend_late,    .resume_early   = platform_resume_early,    .resume     = platform_resume,};EXPORT_SYMBOL_GPL(platform_bus_type);总线bus是联系driver和device的中间枢纽。Device通过所属的bus找到driver.struct bus_type {    const char      * name;    struct subsystem    subsys;    struct kset     drivers;  // drivers-〉list链表包含了所有注册到该bus的driver.    struct kset     devices; // devices ->list链表包含了所有注册到该bus的devices.    struct klist        klist_devices; //    struct klist        klist_drivers;    struct blocking_notifier_head bus_notifier;    struct bus_attribute    * bus_attrs;    struct device_attribute * dev_attrs;    struct driver_attribute * drv_attrs;    int     (*match)(struct device * dev, struct device_driver * drv);    int     (*uevent)(struct device *dev, char **envp,                  int num_envp, char *buffer, int buffer_size);    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 (*suspend_late)(struct device * dev, pm_message_t state);    int (*resume_early)(struct device * dev);    int (*resume)(struct device * dev);};在此，我们需要关注一下platform_match()和platform_drv_probe()函数。platform_match() 

函数确定驱动与设备的关联，而platform_drv_probe()函数会在随后介绍的函数中被调用。//比较驱动信息中的name与设备信息中的name两者是否一致static int platform_match(struct device * dev, struct device_driver * drv){struct platform_device *pdev = container_of(dev, struct platform_device, dev);//通过device找到他所属的platform_devicereturn (strncmp(pdev->name, drv->name, BUS_ID_SIZE) = = 0);} linux kernel源码中有一个神奇的container_of宏，可以根据一个结构体中成员的地址计算出结构体自身的地址。完全可以这样理解container_of宏：#define container_of(ptr, type, member) (type *)((char *)ptr - offset_of(type,member)) 

 对于实现匹配关系的设备和驱动应有如下关系：platform_device -〉device ：该device通过链表连接到BUS上.platform_driver-〉driver（device_driver类型的结构体）:该device通过链表连接到BUS上.platform_device -〉device->device_driver(指针)，该指针指向了platform_driver-〉driver。这样platform_device、platform_driver 就通过platform_device -〉device联系在一起了。因此我们可以通过platform_device -〉device 找到对应的platform_device和platform_driver。这样就很容易理解下面的platform_drv_probe函数了：static int platform_drv_probe(struct device *_dev){    struct platform_driver *drv = to_platform_driver(_dev->driver);    struct platform_device *dev = to_platform_device(_dev);    return drv->probe(dev);//转去执行platform_driver中定义的probe函数。}。对于挂到总线上的设备、驱动是通过：kset、kobject建立各个层次之间的联系。对于kset、kobject。可以参考DDR3设备管理的章节。至此对设备（device）、总线（bus）、驱动（device_driver）的关系有了一个大概的了解。对于2.6内核中更上面一层的封装：platform_device、platform_driver也有了大概的了解。1.3   driver_register()函数在文件drivers/base/driver.c中，实现了driver_register()函数。在此函数中，

初始化结构体struct device_driver中的klist_device和unloaded字段，通过klist_device字段，

可以保存此驱动支持的设备链表，通过“完成”接口机制，完成线程间的同步。

链表和“完成”接口的详细信息可以参考文献［1］。返回bus_add_driver()函数的运行结果。/** *driver_register - register driver with bus *@drv:driver to register *We pass off most of the work to the bus_add_driver() call, *since most of the things we have to do deal with the bus structures. *The one interesting aspect is that we setup drv->unloaded *as a completion that gets complete when the driver reference count reaches 0. */ int driver_register(struct device_driver * drv) { //如果总线的方法和设备自己的方法同时存在,将打印告警信息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); } klist_init(&drv->klist_devices, NULL, NULL); //将driver驱动上的设备链表清空init_completion(&drv->unloaded); return bus_add_driver(drv); //将本driver驱动注册登记到drv->bus所在的总线上。在内核中以driver成员变量kobject，表示driver.所谓的注册即是： driver中的内核成员对象kobject的链表（kobj->entry）,

加入到bus总线的bus_type ->kset->list 链表中。这样就可以通过总线，找到所有定义在该总线下的kobject(driver).} 1.4 bus_add_driver()函数在文件drivers/base/bus.c中实现了bus_add_driver()函数，它通过语句

klist_add_tail(&drv->knode_bus, &bus->klist_drivers); 

将驱动信息保存到总线结构中，在设备注册过程中，我们就可以明白此语句的作用了。在此语句之前，调用了driver_attach()函数。/** *bus_add_driver - Add a driver to the bus. *@drv:driver. * */ int bus_add_driver(struct device_driver *drv) {    struct bus_type * bus = get_bus(drv->bus); //获取总线内容，即前面定义的platform_bus_typeint error = 0; if (!bus) return 0; pr_debug("bus %s: add driver %s\n", bus->name, drv->name);  /*kobject_set_name ：设置kboj->name[KOBJ_NAME_LEN]数组内容,如果KOBJ_NAME_LEN长度不够,

会调用kmalloc申请之后kobj->k_name指针或者指向kboj->name或者指向kmalloc返回地址*/error = kobject_set_name(&drv->kobj, "%s", drv->name); //设置kboj->name成员= drv->nameif (error) goto out_put_bus; //释放总线drv->kobj.kset = &bus->drivers;  //设置device_driver结构体的kobj.kset成员变量（是一个kset指针变量）。

 很重要，它指向总线(bus)的kset成员，bus->drivers成员drivers为kset类型。在platform_driver_register （）

函数中有如下总线赋值语句：drv->driver.bus = &platform_bus_type; platform_bus_type为内核定义的一类总线(bus)。此处的drv->kobj.kset指针指向了总线(bus) 的kset成员。

总线的kset成员是kobject的顶层容器，包含了定义在该总线下面所有的kobject。/******************************************************************//* kobject_register()理解：把drv的kobj登记到管理它的bus->kset集合上去。同时再根据层级关系创建相应的目录文件 。注册登记该kobj,如果该kobj属于某个kset,那么将自己的entry节点(list_head)挂接到该kset的list链表上,以示自己需要

该kset的滋润,同时kobj->parent=&kset->kobj,parent指向kset用来管理自己的kobj如果该kobj的parent已经定义，那么简单的将parent的引用计数加1

（如果该kobj不属于kset,而属于parent,那么简单的将parent的引用计数加1.）对于kobj属于某个kset的情况,可以实现kset向下查找kobj,也可以实现kobj向上查找kset。对于kobj属于某个parent的情况,查找只能是单向的,只能kobj找到parent,parent不能查找该parent挂接的kobj们。

parent是用来明显建立亲子关系图的标志性变量,当然在kset也能若隐若现的显露出这种关系,但总不如parent正宗和高效。

之后调用create_dir()创建该kobj在sysfs中的目录文件最后调用kobject_uevent()将KOBJ_ADD事件通知到用户空间的守护进程*/if ((error = kobject_register(&drv->kobj))) //将driver挂到bus总线上。goto out_put_bus; error = driver_attach(drv); //查找所有注册在该bus上的device，当有device的name和driver->name一样时。

即找到了该driver对应的设备。在里面调用的really_probe()函数中，实现了设备与驱动的绑定。

语句如下：dev->driver = drv;和ret = drv->probe(dev)if (error) goto out_unregister; klist_add_tail(&drv->knode_bus, &bus->klist_drivers); module_add_driver(drv->owner, drv); /*所以一个驱动需要维持住1个klist链条和一个kobj层次结构--驱动drv->kobj对象,内核一方面使用

该kobj在sysfs中建立统一的与该kobj对应的目录对象供用户空间访问,另一方面使用该kobj的引用计数

来获悉该kobj设备的繁忙与空闲情况,//当本kobj对象的引用计数到达0时,只要其他条件允许,那么说明集成本kobj的结构体对象不再使用,

内核得知这个情况很重要,因为这对内核进行进一步的决策提供了详细的证据资料,进而对物理设备进行细致

的电源管理成了可能,//如:当hub1上的所有端口设备都被拔掉之后,hub1就可以安全的进入省电模式了,而这个功能在2.4内核中是找不到的.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", __FUNCTION__, drv->name); } error = add_bind_files(drv); if (error) { /* Ditto */ printk(KERN_ERR "%s: add_bind_files(%s) failed\n", __FUNCTION__, drv->name); } return error; out_unregister: kobject_unregister(&drv->kobj); out_put_bus: put_bus(bus); return error; } 下面说明设备驱动是如何知道总线对应设备的1.5 dd.c文件driver_attach()函数在文件drivers/base/dd.c中，实现了设备与驱动交互的核心函数。1.5.1 driver_attach()函数函数driver_attach()返回bus_for_each_dev()函数的运行结果。bus_for_each_dev()函数的原型如下：int bus_for_each_dev(struct bus_type *bus, struct device *start, void *data, int (*fn) (struct device *, void *));该函数迭代了在总线上的每个设备，将相关的device结构传递给fn，同时传递data值。如果start是NULL，

将从总线上的第一个设备开始迭代；否则将从start后的第一个设备开始迭代。如果fn返回一个非零值，将停止迭代，

而这个值也会从该函数返回（摘自<<Linux设备驱动程序>>第三版）。该函数是如何知道总线上的每个设备的呢？在设备注册过程中，我会详细介绍。/* *drivers/base/dd.c - The core device/driver interactions. * * This file contains the (sometimes tricky) code that controls the *interactions between devices and drivers, which primarily includes *driver binding and unbinding. *//** *driver_attach - try to bind driver to devices. *@drv:driver. * *Walk the list of devices that the bus has on it and try to *match the driver with each one.If driver_probe_device() *returns 0 and the @dev->driver is set, we've found a *compatible pair. */ int driver_attach(struct device_driver * drv) {     return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach); } 1.5.2 __driver_attach()函数函数__driver_attach()在调用driver_probe_device()函数前，需要进行线程间的互斥处理。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 (dev->parent)down(&dev->parent->sem); down(&dev->sem); if (!dev->driver) driver_probe_device(drv, dev); up(&dev->sem); if (dev->parent) up(&dev->parent->sem); return 0; }  1.5.3 driver_probe_device()函数在driver_probe_device()函数中，调用了match函数platform_match()，如果它返回0，

表示驱动与设备不一致，函数返回；否则，调用really_probe()函数。/** * driver_probe_device - attempt to bind device & driver together * @drv: driver to bind a device to * @dev: device to try to bind to the driver * * First, 

we call the bus's match function, if one present, which should * compare the device 

IDs the driver supports with the device IDs of the * device. Note we don't do this 

ourselves because we don't know the * format of the ID structures, nor what is to be 

considered a match and * what is not. * * This function returns 1 if a match is found, 

an error if one occurs *(that is not -ENODEV or -ENXIO), and 0 otherwise. 

* * This function must be called with @dev->sem held.  When called for a * USB interface,

 @dev->parent->sem must be held as well. */ int driver_probe_device(struct device_driver * drv, struct device * dev) { struct stupid_thread_structure *data;     struct task_struct *probe_task;     int ret = 0;     if (!device_is_registered(dev))        return -ENODEV;     if (drv->bus->match && !drv->bus->match(dev, drv))        goto done;     pr_debug("%s: Matched Device %s with Driver %s\n",         drv->bus->name, dev->bus_id, drv->name);     data = kmalloc(sizeof(*data), GFP_KERNEL);   if (!data)        return -ENOMEM;     data->drv = drv;     data->dev = dev; if (drv->multithread_probe) {        probe_task = kthread_run(really_probe, data,                    "probe-%s", dev->bus_id);        if (IS_ERR(probe_task))            ret = really_probe(data);     } else        ret = really_probe(data); done:     return ret; }struct stupid_thread_structure {     struct device_driver *drv;     struct device *dev; }; 1.5.4 really_probe()函数在really_probe()函数中，实现了设备与驱动的绑定。语句如下：dev->driver = drv;和ret = drv->probe(dev); probe()函数的实现如下：include/linux/platform_device.h#define to_platform_device(x) container_of((x), struct platform_device, dev)drivers/base/platform.c#define to_platform_driver(drv) (container_of((drv), struct platform_driver, driver))static int platform_drv_probe(struct device *_dev) { struct platform_driver *drv = to_platform_driver(_dev->driver);     struct platform_device *dev = to_platform_device(_dev);     return drv->probe(dev); } 在此函数中，回调了我们在i2c-at91.c文件中实现的探测函数at91_i2c_probe()，至此，平台驱动的注册过程结束。static atomic_t probe_count = ATOMIC_INIT(0); static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue); static int really_probe(void *void_data) {     struct stupid_thread_structure *data = void_data;     struct device_driver *drv = data->drv;     struct device *dev = data->dev; int ret = 0;     atomic_inc(&probe_count);     pr_debug("%s: Probing driver %s with device %s\n",         drv->bus->name, drv->name, dev->bus_id); WARN_ON(!list_empty(&dev->devres_head)); dev->driver = drv;     if (driver_sysfs_add(dev)) {        printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",            __FUNCTION__, dev->bus_id);        goto probe_failed;     }     if (dev->bus->probe) {        ret = dev->bus->probe(dev);        if (ret)            goto probe_failed;     } else if (drv->probe) {        ret = drv->probe(dev);        if (ret)            goto probe_failed;     }     //设备与驱动绑定后，对系统中已注册的组件进行事件通知。    driver_bound(dev);     ret = 1;     pr_debug("%s: Bound Device %s to Driver %s\n",         drv->bus->name, dev->bus_id, 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->bus_id, ret);     }    /* * Ignore errors returned by ->probe so that the next driver can try  * its luck. */ ret = 0; done:     kfree(data);     atomic_dec(&probe_count);     wake_up(&probe_waitqueue);     return ret; }