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、

[cpp]
view plaincopy

<span style="font-size:16px;">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);
}</span>

2、

[cpp]
view plaincopy

<span style="font-size:16px;">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;
}</span>

3、

[cpp]
view plaincopy

<span style="font-size:16px;">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;
}</span>

4、驱动的匹配关键是上面函数中的

[cpp]
view plaincopy

<span style="font-size:16px;"> 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>

[cpp]
view plaincopy

<span style="font-size:16px;">int driver_attach(struct device_driver *drv)
{
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}</span>

[cpp]
view plaincopy

<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;
}</span>

//寻找到下一个设备的节点

[cpp]
view plaincopy

<span style="font-size:16px;">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;
}</span>

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

[cpp]
view plaincopy

<span style="font-size:16px;">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;
}
</span>

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

[cpp]
view plaincopy

<span style="font-size:16px;">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
}</span>

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

[cpp]
view plaincopy

<span style="font-size:16px;">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);
}</span>

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

[cpp]
view plaincopy

<span style="font-size:16px;">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;
}</span>

[cpp]
view plaincopy

<span style="font-size:16px;">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;
}</span>

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