关于platform_driver 是如何匹配 platform_device的和如何调用到platform_driver中的probe函数的研究

在linux中platform平台驱动又三大部分组成，第一是bus、第二是驱动、第三是设备。

第一总线也就是platform_bus，总线也是一种特殊的device，到底层下面还是要调用device_register来注册该总线设备，然后是用来注册总线的属性结构体 bus_type（platform_bus_type），至此platform平台的总线已经准备好。具体介绍可以看我另一篇博客。
第二是设备，platform_device，它的注册流程是：platform_device_register(struct platform_device *pdev)->device_initialize(&pdev->dev)->platform_device_add(pdev)->pdev->dev.bus = &platform_bus_type->device_add(&pdev->dev)->把设备挂在虚拟的platform
bus下。
第三是驱动，现在总线、设备都准备好了，然后等着驱动来匹配设备进行驱动，具体的驱动匹配设备流程如下：
1、

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int platform_driver_register(struct platform_driver *drv)

{

drv->driver.bus = &platform_bus_type;//驱动的总线类型指向platform_bus_type

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);

}

2、

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int driver_register(struct device_driver *drv)

{

int ret;

struct device_driver *other;



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

//检测总线的操作函数和驱动的操作函数是否同时存在,同时存在则提示使用总线提供的操作函数

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);

//查找这个驱动是否已经在总线上注册，并增加引用计数，若已经注册，则返回提示信息。

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

if (other) {

//如果已经被注册，则返回提示错误并且减少引用计数。

put_driver(other);

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

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

return -EEXIST;

}

//若还没有注册，则在总线上注册该驱动

ret = bus_add_driver(drv);

if (ret)

return ret;

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

if (ret)

bus_remove_driver(drv);

return ret;

}

3、


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int bus_add_driver(struct device_driver *drv)

{

struct bus_type *bus;

struct driver_private *priv;

int error = 0;

//用于增加该bus所属的顶层bus的kobject的引用计数，返回的是其所属的顶层bus的指针。

bus = bus_get(drv->bus);

if (!bus)

return -EINVAL;



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



priv = kzalloc(sizeof(*priv), GFP_KERNEL);

if (!priv) {

error = -ENOMEM;

goto out_put_bus;

}

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

//将这两个结构体连接起来

priv->driver = drv;

drv->p = priv;

//指向顶层的bus的p->drivers_kset

//设置私有数据的父容器,在这一步中,设置了kset为platform下的drivers_kset结构,也就是drivers呢个目录

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

//初始化kobj对象,设置容器操作集并建立相应的目录,这里由于没有提供parent,所以会使用父容器中的kobj为父对象

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

"%s", drv->name);

if (error)

goto out_unregister;

//检测所属总线的drivers_autoprobe属性是否为真

//为真则进行与设备的匹配,到这里,就会与我们之前注册的test_device连接上了,

//至于如何连接,进行了什么操作,将在别的文章中详细描述

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

error = driver_attach(drv);

if (error)

goto out_unregister;

}

//挂载到所属总线驱动链表上

klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);

module_add_driver(drv->owner, drv);

//建立uevent属性文件

error = driver_create_file(drv, &driver_attr_uevent);

if (error) {

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

__func__, drv->name);

}

//建立设备属性文件

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);

}

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:

kfree(drv->p);

drv->p = NULL;

kobject_put(&priv->kobj);

out_put_bus:

bus_put(bus);

return error;

}

4、驱动的匹配关键是上面函数中的

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if (drv->bus->p->drivers_autoprobe) {//drivers_autoprobe在初始化的时候定义为1，系统则会调用下面的driver_attach函数进行驱动与设备的匹配

error = driver_attach(drv);

if (error)

goto out_unregister;

}</span>



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int driver_attach(struct device_driver *drv)

{

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

}</span>

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<span style="font-size:16px;"> //bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);

int bus_for_each_dev(struct bus_type *bus, struct device *start,

void *data, int (*fn)(struct device *, void *))

{/*



struct klist_iter {

struct klist *i_klist;

struct klist_node *i_cur;

};



*/

struct klist_iter i;

struct device *dev;

int error = 0;



if (!bus)

return -EINVAL;

//如果第三个参数不为空就增加引用计数

klist_iter_init_node(&bus->p->klist_devices, &i,

(start ? &start->p->knode_bus : NULL));//一直是NULL

//经过上面的宏之后，i实际上变成了i->i_klist=&bus->p->klist_devices,bus->p->klist_devices指向的是挂接在它上面的所有的设备的指针

while ((dev = next_device(&i)) && !error)

//fu函数传入的是device的指针和device_driver的指针，

error = fn(dev, data);

//如果klist_iter_init_node第三个参数不为空则减少引用计数

klist_iter_exit(&i);

return error;

}

//寻找到下一个设备的节点

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static struct device *next_device(struct klist_iter *i)

{

struct klist_node *n = klist_next(i);

struct device *dev = NULL;

struct device_private *dev_prv;



if (n) {

dev_prv = to_device_private_bus(n);

dev = dev_prv->device;

}

return dev;

}

函数error = fn(dev, data)的原型如下：
传进来的参数第一个参数为不断遍历到的设备节点的指针，第二个参数为固定的一个驱动所对应的struct device_driver *drv指针，这样就实现驱动和设备的匹配

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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.

*/

//当设备和驱动的名字不匹配的时候返回的是0，然后就会调用下面的return 0；

if (!driver_match_device(drv, dev))

return 0;



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

down(&dev->parent->sem);

down(&dev->sem);

if (!dev->driver)

driver_probe_device(drv, dev);//调用探测函数进行探测，并且调用platform_driver中的probe函数

up(&dev->sem);

if (dev->parent)

up(&dev->parent->sem);



return 0;

}

在上面有两个比较关键的函数driver_match_device(dre,dev),函数原型如下：

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static inline int driver_match_device(struct device_driver *drv,

struct device *dev)

{

return drv->bus->match ? drv->bus->match(dev, drv) : 1;//无论设备与驱动是否匹配成功都会返回1

}

当驱动的指针不为空的时候，这个drv->bus所指向的的这个驱动所属的的总线的bus_type中的match函数，然后传进去的是该驱动的指针和设备的指针

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static int platform_match(struct device *dev, struct device_driver *drv)

{

struct platform_device *pdev = to_platform_device(dev);

struct platform_driver *pdrv = to_platform_driver(drv);



/* match against the id table first */

if (pdrv->id_table)//为空，不会被调用

return platform_match_id(pdrv->id_table, pdev) != NULL;



/* fall-back to driver name match */

return (strcmp(pdev->name, drv->name) == 0);

}

最后调用驱动的probe函数进行设备的探测
driver_probe_device(drv, dev);//调用探测函数进行探测，并且调用platform_driver中的probe函数

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int driver_probe_device(struct device_driver *drv, struct device *dev)

{

int ret = 0;

//再次检查设备有没有在总线上注册，当发现还没有注册的时候，返回一个错误

if (!device_is_registered(dev))

return -ENODEV;



pr_debug("bus: '%s': %s: matched device %s with driver %s\n",

drv->bus->name, __func__, dev_name(dev), drv->name);



ret = really_probe(dev, drv);



return ret;

}



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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));

//找到了设备的驱动，并且将dev->driver指针指向自己的这个驱动

dev->driver = drv;

if (driver_sysfs_add(dev)) {//在sys目录下建立连接指向自己的在sys中的drivers

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

__func__, dev_name(dev));

goto probe_failed;

}

//在bus_type platform_bus_type中并没有设置probe函数，所以下面函数并不会被调用

if (dev->bus->probe) {

ret = dev->bus->probe(dev);

if (ret)

goto probe_failed;

} else if (drv->probe) {//上面总线没有probe函数，所以直接调用驱动当中的probe函数

ret = drv->probe(dev);

if (ret)

goto probe_failed;

}



driver_bound(dev);

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;

}

至此platform_driver的probe函数实现了调用并且匹配了platform_device