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前几日读书会，谈到linux中driver和device的匹配问题，我认为是通过设备名来匹配的，因为我之前看过platform的驱动，它就是通过设备name和驱动name来进行匹配，所以我确信linux里边所有的驱动和设备都是这样匹配的。但师兄A提出了反对意见，并举pci设备和pci驱动的匹配过程为例。我深信自己的理解是正确的，下来以后分秒必争的查看了内核源代码，结果发现：我们的理解都是正确的，但又都是不正确的！
先以pci设备和pci驱动的匹配过程为例：
static struct pci_driver serial_pci_driver = {
.name = "serial",
.probe = pciserial_init_one,
.remove = __devexit_p(pciserial_remove_one),
#ifdef CONFIG_PM
.suspend = pciserial_suspend_one,
.resume = pciserial_resume_one,
#endif
.id_table = serial_pci_tbl,
};
static int __init serial8250_pci_init(void)
{
return pci_register_driver(&serial_pci_driver);
}
分析：
#define pci_register_driver(driver) \
__pci_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)
int __pci_register_driver(struct pci_driver *drv, struct module *owner,
const char *mod_name)
{
...
drv->driver.bus = &pci_bus_type;
error = driver_register(&drv->driver);
...
}
仅仅抓取两句关键代码，后面会用到
driver_register -> bus_add_driver -> driver_attach(&driver->driver);
int driver_attach(struct device_driver *drv)
{
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
//遍历总线上的所有设备，每遍历一个设备，就调用一次__driver_attach来和驱动进行匹配
}
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 (drv->bus->match && !drv->bus->match(dev, drv))
return 0;
if (dev->parent) /* Needed for USB */
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;
}
我最关注的是这句代码：
if (drv->bus->match && !drv->bus->match(dev, drv))
return 0;
这句代码揭露了匹配的过程。
这是一种面向对像的思想，你是pci设备，那就调用pci总线的match函数；你是其他总线的设备
那就调用相应的其他的match函数。由于我们是pci的驱动(我们注册驱动使用的函数是pci_register_driver)并且在前面有：
drv->driver.bus = &pci_bus_type;让我们看看pci_bus_type是和角色：
struct bus_type pci_bus_type = {
.name = "pci",
.match = pci_bus_match,
.uevent = pci_uevent,
.probe = pci_device_probe,
.remove = pci_device_remove,
.shutdown = pci_device_shutdown,
.dev_attrs = pci_dev_attrs,
.pm = PCI_PM_OPS_PTR,
};
很明显，我们将进入pci_bus_match
static int pci_bus_match(struct device *dev, struct device_driver *drv)
{
struct pci_dev *pci_dev = to_pci_dev(dev);
struct pci_driver *pci_drv = to_pci_driver(drv);
const struct pci_device_id *found_id;
found_id = pci_match_device(pci_drv, pci_dev);//对pci驱动和设备进行匹配
if (found_id)
return 1;
return 0;
}
static const struct pci_device_id *pci_match_device(struct pci_driver *drv,
struct pci_dev *dev)
{
struct pci_dynid *dynid;
/* Look at the dynamic ids first, before the static ones */
spin_lock(&drv->dynids.lock);
list_for_each_entry(dynid, &drv->dynids.list, node) {
if (pci_match_one_device(&dynid->id, dev)) {
spin_unlock(&drv->dynids.lock);
return &dynid->id;
}
}
spin_unlock(&drv->dynids.lock);
return pci_match_id(drv->id_table, dev);
}
static inline const struct pci_device_id *
pci_match_one_device(const struct pci_device_id *id, const struct pci_dev *dev)
{
if ((id->vendor == PCI_ANY_ID || id->vendor == dev->vendor) &&
(id->device == PCI_ANY_ID || id->device == dev->device) &&
(id->subvendor == PCI_ANY_ID || id->subvendor == dev->subsystem_vendor) &&
(id->subdevice == PCI_ANY_ID || id->subdevice == dev->subsystem_device) &&
!((id->class ^ dev->class) & id->class_mask))
return id;
return NULL;
}
这就是具体的匹配过程，这个过程大家看代码应该可以明白。
假如匹配，那么会返回一个pci_device_id类型的指针。
在__driver_attach函数里边继续往下看，有一句：
if (!dev->driver)
driver_probe_device(drv, dev);
假如 这个设备还没有“名花有主”，那么调用driver_probe_device
int driver_probe_device(struct device_driver *drv, struct device *dev)
{
int ret = 0;
if (!device_is_registered(dev))
return -ENODEV;
if (drv->bus->match && !drv->bus->match(dev, drv))
goto done;
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);
done:
return ret;
}
static int really_probe(struct device *dev, struct device_driver *drv)
{
...
if (dev->bus->probe) {
ret = dev->bus->probe(dev);
if (ret)
goto probe_failed;
} else if (drv->probe) {
ret = drv->probe(dev); //终于进入了我们注册的驱动的probe函数
if (ret)
goto probe_failed;
}
...
}
总结一下，pci驱动和pci设备的匹配不是通过名字来进行匹配的，具体过程上面已经说清楚了。而且，通过上面的分析，大家可以看出来
内核使用的是面向对象的思想，不同的总线它的匹配策略是不一样的。
附：
1.platform总线的匹配策略：
static int platform_match(struct device *dev, struct device_driver *drv)
{
struct platform_device *pdev;
pdev = container_of(dev, struct platform_device, dev);
return (strcmp(pdev->name, drv->name) == 0);
}
可见platform总线设备和驱动的匹配策略很简单，仅仅是比较name域是否相同
2.usb总线的匹配策略：
static int usb_device_match(struct device *dev, struct device_driver *drv)
{
/* devices and interfaces are handled separately */
if (is_usb_device(dev)) {
/* interface drivers never match devices */
if (!is_usb_device_driver(drv))
return 0;
/* TODO: Add real matching code */
return 1;
} else {
struct usb_interface *intf;
struct usb_driver *usb_drv;
const struct usb_device_id *id;
/* device drivers never match interfaces */
if (is_usb_device_driver(drv))
return 0;
intf = to_usb_interface(dev);
usb_drv = to_usb_driver(drv);
id = usb_match_id(intf, usb_drv->id_table);
if (id)
return 1;
id = usb_match_dynamic_id(intf, usb_drv);
if (id)
return 1;
}
return 0;
}
usb总线设备和驱动的匹配策略则比较复杂。
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