1. USB总线
1.1 usb总线定义
在linux 设备模型中，总线由bus_type 结构表示，我们所用的 I2C、SPI、USB 都是用这个结构体来定义的。该结构体定义在 include/linux/device.h文件中：
struct bus_type {
const char *name;
const char *dev_name;
struct device *dev_root;
const struct attribute_group **bus_groups;
const struct attribute_group **dev_groups;
const struct attribute_group **drv_groups;
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 (*online)(struct device *dev);
int (*offline)(struct device *dev);
int (*suspend)(struct device *dev, pm_message_t state);
int (*resume)(struct device *dev);
int (*num_vf)(struct device *dev);
int (*dma_configure)(struct device *dev);
const struct dev_pm_ops *pm;
const struct iommu_ops *iommu_ops;
struct subsys_private *p;
struct lock_class_key lock_key;
bool need_parent_lock;
};
其中部分字段的含义如下：
- name：总线名称；
- bus_groups：总线属性;
- dev_groups：该总线上所有设备的默认属性;
- drv_groups：该总线上所有驱动的默认属性；
- match：当有新的设备或驱动添加到总线上时match函数被调用，如果设备和驱动可以匹配，返回0；
- uevent：当一个设备添加、移除或添加环境变量时，函数调用；
- probe：当有新设备或驱动添加时，probe函数调用，并且回调该驱动的probe函数来初始化相关联的设备；
- remove：设备移除时调用remove函数；
- shutdown：设备关机时调用shutdown函数；
- suspend：设备进入睡眠时调用suspend函数；
- resume：设备唤醒时调用resume函数；
- pm：总线的电源管理选项，并回调设备驱动的电源管理模块；
usb总线是 bus_type 类型的全局变量，这个变量已经被 linux 内核赋值好了，其结构体成员对应的函数也已经在内核里面写好，定义在drivers/usb/core/driver.c：
struct bus_type usb_bus_type = {
.name = "usb",
.match = usb_device_match,
.uevent = usb_uevent,
.need_parent_lock = true,
};
这里我们重点关注BUS匹配函数usb_device_match即可。
1.2 usb设备和驱动匹配
1.2.1 usb_device_match
usb_bus_type 中的usb_device_match就是用来进行驱动和设备匹配的函数，不同的总线对应的match 函数肯定不一样，这个我们不用管，内核都会写好。
我们所用的BUS总线对应的 match 函数是 usb_device_match函数，该函数定义在drivers/usb/core/driver.c：
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 if (is_usb_interface(dev)) {
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;
}
在介绍这段之前，我们先来介绍一下usb设备和usb接口的区别：
- 对于usb设备，使用struct usb_device类型表示，dev成员的type成员会设置成usb_device_type；
- 对于usb接口，使用struct usb_interface类型表示，dev成员的type成员则会设成usb_if_device_type；
接着我们再来说一下usb设备驱动和usb接口驱动的区别：
- 对于usb设备驱动，使用struct usb_device_driver类型表示，是通过usb_register_device_driver函数来注册的，这个后面会介绍；
- 对于usb接口驱动，使用struct usb_driver类型表示，是通过usb_register函数来注册的，这个后面会介绍；
不管是设备驱动usb_device_driver，还是接口驱动usb_driver数据结构中都包含了struct usbdrv_wrap项，其定义如下：
struct usbdrv_wrap {
struct device_driver driver;
int for_devices;
}
数据结构中的for_devices用来表示该驱动是设备驱动还是接口驱动，如果为设备驱动，则在用usb_register_device_driver注册时，会将该变量for_devices设置成1，而接口驱动则设为0。usb_device_match中的is_usb_device_driver函数就是通过获取上而结构中的for_devices来进行判断是设备还是接口驱动的。
接着我们再来分析一下上面的代码，该函数有两个参数：设备和设备驱动，该函数可以分为两部分，一部分用于匹配usb设备，另一部分用于匹配usb接口；
- 对于usb设备，当匹配的是usb设备驱动时，将会匹配成功，实际上所有的usb设备对应的设备驱动都是usb_generic_driver，该设备驱动在usb子系统初始化时注册；
- 对于usb接口，先用is_usb_device_driver来进行判断，如果不是usb设备驱动则继续判断，否则退出；然后再通过usb_match_id函数来判断接口和接口驱动中的usb_device_id是否匹配。
驱动工程师的工作基本上集中在接口驱动上，所以通常是通过usb_register来注册usb接口驱动的。
1.2.2 usb_match_id
const struct usb_device_id *usb_match_id(struct usb_interface *interface,
const struct usb_device_id *id)
{
/* proc_connectinfo in devio.c may call us with id == NULL. */
if (id == NULL)
return NULL;
/* It is important to check that id->driver_info is nonzero,
since an entry that is all zeroes except for a nonzero
id->driver_info is the way to create an entry that
indicates that the driver want to examine every
device and interface. */
for (; id->idVendor || id->idProduct || id->bDeviceClass ||
id->bInterfaceClass || id->driver_info; id++) {
if (usb_match_one_id(interface, id))
return id;
}
return NULL;
}
1.2.3 usb_match_one_id
/* returns 0 if no match, 1 if match */
int usb_match_device(struct usb_device *dev, const struct usb_device_id *id)
{
if ((id->match_flags & USB_DEVICE_ID_MATCH_VENDOR) &&
id->idVendor != le16_to_cpu(dev->descriptor.idVendor))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_PRODUCT) &&
id->idProduct != le16_to_cpu(dev->descriptor.idProduct))
return 0;
/* No need to test id->bcdDevice_lo != 0, since 0 is never
greater than any unsigned number. */
if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_LO) &&
(id->bcdDevice_lo > le16_to_cpu(dev->descriptor.bcdDevice)))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_HI) &&
(id->bcdDevice_hi < le16_to_cpu(dev->descriptor.bcdDevice)))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_CLASS) &&
(id->bDeviceClass != dev->descriptor.bDeviceClass))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_SUBCLASS) &&
(id->bDeviceSubClass != dev->descriptor.bDeviceSubClass))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_DEV_PROTOCOL) &&
(id->bDeviceProtocol != dev->descriptor.bDeviceProtocol))
return 0;
return 1;
}
/* returns 0 if no match, 1 if match */
int usb_match_one_id_intf(struct usb_device *dev,
struct usb_host_interface *intf,
const struct usb_device_id *id)
{
/* The interface class, subclass, protocol and number should never be
* checked for a match if the device class is Vendor Specific,
* unless the match record specifies the Vendor ID. */
if (dev->descriptor.bDeviceClass == USB_CLASS_VENDOR_SPEC &&
!(id->match_flags & USB_DEVICE_ID_MATCH_VENDOR) &&
(id->match_flags & (USB_DEVICE_ID_MATCH_INT_CLASS |
USB_DEVICE_ID_MATCH_INT_SUBCLASS |
USB_DEVICE_ID_MATCH_INT_PROTOCOL |
USB_DEVICE_ID_MATCH_INT_NUMBER)))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_CLASS) &&
(id->bInterfaceClass != intf->desc.bInterfaceClass))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_SUBCLASS) &&
(id->bInterfaceSubClass != intf->desc.bInterfaceSubClass))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_PROTOCOL) &&
(id->bInterfaceProtocol != intf->desc.bInterfaceProtocol))
return 0;
if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_NUMBER) &&
(id->bInterfaceNumber != intf->desc.bInterfaceNumber))
return 0;
return 1;
}
/* returns 0 if no match, 1 if match */
int usb_match_one_id(struct usb_interface *interface,
const struct usb_device_id *id)
{
struct usb_host_interface *intf;
struct usb_device *dev;
/* proc_connectinfo in devio.c may call us with id == NULL. */
if (id == NULL)
return 0;
intf = interface->cur_altsetting;
dev = interface_to_usbdev(interface);
if (!usb_match_device(dev, id))
return 0;
return usb_match_one_id_intf(dev, intf, id);
}
实际上这里就是将usb设备（usb设备的设备描述符信息、以及接口描述符信息）的信息和usb_driver驱动id_table信息进行匹配，如果匹配成功，则返回1，否则返回0.
1.3 usb总线注册
usb的总线注册是由usb_init函数完成，该函数也是usb子系统的入口函数，代码实现在drivers/usb/core/usb.c文件中，模块入口/出口函数如下：
subsys_initcall(usb_init);
module_exit(usb_exit);
usb_init函数代码：
/*
* Init
*/
static int __init usb_init(void)
{
int retval;
if (usb_disabled()) {
pr_info("%s: USB support disabled\n", usbcore_name);
return 0;
}
usb_init_pool_max();
usb_debugfs_init();
usb_acpi_register();
retval = bus_register(&usb_bus_type);
if (retval)
goto bus_register_failed;
retval = bus_register_notifier(&usb_bus_type, &usb_bus_nb);
if (retval)
goto bus_notifier_failed;
retval = usb_major_init();
if (retval)
goto major_init_failed;
retval = usb_register(&usbfs_driver);
if (retval)
goto driver_register_failed;
retval = usb_devio_init();
if (retval)
goto usb_devio_init_failed;
retval = usb_hub_init();
if (retval)
goto hub_init_failed;
retval = usb_register_device_driver(&usb_generic_driver, THIS_MODULE);
if (!retval)
goto out;
usb_hub_cleanup();
hub_init_failed:
usb_devio_cleanup();
usb_devio_init_failed:
usb_deregister(&usbfs_driver);
driver_register_failed:
usb_major_cleanup();
major_init_failed:
bus_unregister_notifier(&usb_bus_type, &usb_bus_nb);
bus_notifier_failed:
bus_unregister(&usb_bus_type);
bus_register_failed:
usb_acpi_unregister();
usb_debugfs_cleanup();
out:
return retval;
}
在usb_init函数中主要有如下的三个主要函数:
- 通过usb_debugfs_init初始化usb debugfs；
- 通过bus_register注册usb总线usb_bus_type；
- 通过bus_register_notifier注册usb总线通知链；
- 通过usb_major_init注册usb控制器字符设备，主设备编号为181，字符设备名称为usb；
- 通过usb_register注册usbfs驱动；
- 通过usb_devio_init注册usb设备字符设备，主设备编号为189，字符设备名称为usb_device；
- 通过usb_hub_init初始化usb hub接口驱动;
- 通过usb_register_device_driver注册usb设备驱动.
2. usb子系统初始化
由于usb_init函数比较复杂，这里就单独一小节进行介绍。
2.1 usb_debugfs_init()
usb_debugfs_init函数定义在drivers/usb/core/usb.c文件中：
static void usb_debugfs_init(void)
{
usb_debug_root = debugfs_create_dir("usb", NULL);
debugfs_create_file("devices", 0444, usb_debug_root, NULL,
&usbfs_devices_fops);
}
其主要作用就是在debug文件系统中创建一个usb目录，然后在usb目录下面创建一个devices的文件。
要使用debugfs下面的usb功能，需要先挂着debug文件系统，具体初始化了啥调试接口,看下usbfs_devices_fops操作函数集。
mount -t debugfs none $(debugfs)
2.2 bus_register(&usb_bus_type)
struct bus_type usb_bus_type = {
.name = "usb",
.match = usb_device_match,
.uevent = usb_uevent,
.need_parent_lock = true,
};
bus_register中创建了两个链表，一个为设备链表，一个为驱动链表：
klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put);
klist_init(&priv->klist_drivers, NULL, NULL);
usb总线设备链表上挂载的是usb设备或者usb接口，而在usb总线驱动链表上挂在的是usb设备驱动或者是usb接口驱动。
无论是usb设备还是usb接口，其设备基类都是struct device，该类型包含一个成员是bus，类型为struct bus_type，会被初始化为usb_bus_type。
无论是usb设备驱动还是usb接口驱动，其驱动基类都是struct device_driver，该类型包含一个成员是bus，类型为struct bus_type，会被初始化为usb_bus_type。
usb总线上设备链表上的设备和驱动链表上的驱动的匹配函数是usb_device_match，这个上面已经介绍过了。
bus_register函数调用后，就会在用户空间生成usb相关文件，执行如下命令：
root:~# ls /sys/bus/usb
devices drivers drivers_autoprobe drivers_probe uevent
/sys/bus/usb/devices里用来存放的是usb设备，/sys/bus/usb/drivers里用来存放的是usb驱动：
root:~# ls /sys/bus/usb/devices
1-0:1.0 2-0:1.0 2-1 2-1:1.0 2-2 2-2.1 2-2:1.0 2-2.1:1.0 2-2.1:1.1 usb1 usb2
root:~# ls /sys/bus/usb/drivers
btusb hub usb usbfs usbhid
2.3 bus_register_notifier(&usb_bus_type,&usb_bus_nb)
bus_register_notifier函数定义在drivers/base/bus.c:
int bus_register_notifier(struct bus_type *bus, struct notifier_block *nb)
{
return blocking_notifier_chain_register(&bus->p->bus_notifier, nb);
}
usb_bus_nb定义在drivers/usb/core/usb.c：
static struct notifier_block usb_bus_nb = {
.notifier_call = usb_bus_notify,
};
这里注册了usb总线通知链，当向usb_bus_type添加删除设备的时候会调用usb_bus_nb指定的notifier_cal方法,即usb_bus_notify：
/*
* Notifications of device and interface registration
*/
static int usb_bus_notify(struct notifier_block *nb, unsigned long action,
void *data)
{
struct device *dev = data;
switch (action) {
case BUS_NOTIFY_ADD_DEVICE: // 添加设备
if (dev->type == &usb_device_type) // usb设备
(void) usb_create_sysfs_dev_files(to_usb_device(dev));
else if (dev->type == &usb_if_device_type) // usb接口
usb_create_sysfs_intf_files(to_usb_interface(dev));
break;
case BUS_NOTIFY_DEL_DEVICE: // 删除设备
if (dev->type == &usb_device_type) // usb设备
usb_remove_sysfs_dev_files(to_usb_device(dev));
else if (dev->type == &usb_if_device_type) // usb接口
usb_remove_sysfs_intf_files(to_usb_interface(dev));
break;
}
return 0;
}
2.4 usb_major_init()
usb_major_init函数定义在drivers/usb/core/file.c：
int usb_major_init(void)
{
int error;
error = register_chrdev(USB_MAJOR, "usb", &usb_fops);
if (error)
printk(KERN_ERR "Unable to get major %d for usb devices\n",
USB_MAJOR);
return error;
}
这里使用register_chrdev向内核注册usb主控制器字符设备，字符设备的名称为usb，字符设备的主设备号为USB_MAJOR(180)，设备操作为usb_fops。
register_chrdev封装了register_chrdev_region、cdev_alloc、cdev_add相关逻辑，这里不介绍了。
其中usb_fops定义为：
static const struct file_operations usb_fops = {
.owner = THIS_MODULE,
.open = usb_open,
.llseek = noop_llseek,
};
2.5 usb_register(&usbfs_driver)
用usb_register宏向linux内核注册usb接口驱动usbfs_driver，usbfs_driver定义在drivers/usb/core/devio.c：
struct usb_driver usbfs_driver = {
.name = "usbfs",
.probe = driver_probe,
.disconnect = driver_disconnect,
.suspend = driver_suspend,
.resume = driver_resume,
};
usb_rigister宏定义在include/linux/usb.h文件中：
/* use a define to avoid include chaining to get THIS_MODULE & friends */
#define usb_register(driver) \
usb_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)
/**
* usb_register_driver - register a USB interface driver
* @new_driver: USB operations for the interface driver
* @owner: module owner of this driver.
* @mod_name: module name string
*
* Registers a USB interface driver with the USB core. The list of
* unattached interfaces will be rescanned whenever a new driver is
* added, allowing the new driver to attach to any recognized interfaces.
*
* Return: A negative error code on failure and 0 on success.
*
* NOTE: if you want your driver to use the USB major number, you must call
* usb_register_dev() to enable that functionality. This function no longer
* takes care of that.
*/
int usb_register_driver(struct usb_driver *new_driver, struct module *owner,
const char *mod_name)
{
int retval = 0;
if (usb_disabled())
return -ENODEV;
new_driver->drvwrap.for_devices = 0;
new_driver->drvwrap.driver.name = new_driver->name;
new_driver->drvwrap.driver.bus = &usb_bus_type;
new_driver->drvwrap.driver.probe = usb_probe_interface;
new_driver->drvwrap.driver.remove = usb_unbind_interface;
new_driver->drvwrap.driver.owner = owner;
new_driver->drvwrap.driver.mod_name = mod_name;
spin_lock_init(&new_driver->dynids.lock);
INIT_LIST_HEAD(&new_driver->dynids.list);
retval = driver_register(&new_driver->drvwrap.driver);
if (retval)
goto out;
retval = usb_create_newid_files(new_driver);
if (retval)
goto out_newid;
pr_info("%s: registered new interface driver %s\n",
usbcore_name, new_driver->name);
out:
return retval;
out_newid:
driver_unregister(&new_driver->drvwrap.driver);
printk(KERN_ERR "%s: error %d registering interface "
" driver %s\n",
usbcore_name, retval, new_driver->name);
goto out;
}
这里首先初始化usb接口驱动里的驱动基类driver，然后调用driver_register进行驱动注册，关于驱动注册函数driver_register具体参考linux驱动移植-总线设备驱动。
这里简单介绍一下driver_register函数执行流程：
- 将usb接口驱动添加到usb总线上(usb_bus_type)；
- 遍历usb总线上的所有usb接口，然后调用usb_device_match进行usb接口驱动和usb接口的匹配；
- 匹配成功后最终会执行usb接口驱动的probe函数，过程中的驱动基类driver的probe函数和 usb_probe_interface 函数都是达到这个目的的中转函数而已。
2.6 usb_devio_init()
usb_devio_init函数实现在drivers/usb/core/devio.c：
int __init usb_devio_init(void)
{
int retval;
retval = register_chrdev_region(USB_DEVICE_DEV, USB_DEVICE_MAX,
"usb_device");
if (retval) {
printk(KERN_ERR "Unable to register minors for usb_device\n");
goto out;
}
cdev_init(&usb_device_cdev, &usbdev_file_operations);
retval = cdev_add(&usb_device_cdev, USB_DEVICE_DEV, USB_DEVICE_MAX);
if (retval) {
printk(KERN_ERR "Unable to get usb_device major %d\n",
USB_DEVICE_MAJOR);
goto error_cdev;
}
usb_register_notify(&usbdev_nb);
out:
return retval;
error_cdev:
unregister_chrdev_region(USB_DEVICE_DEV, USB_DEVICE_MAX);
goto out;
}
首先使用register_chrdev_region来静态注册一组字符设备编号，主设备编号为USB_DEVICE_DEV(189)，次设备编号从0~USB_DEVICE_MAX，字符设备名称为usb_device。
然后使用cdev_init初始化字符设备结构体cdev，usbdev_file_operations结构体放入cdev-> ops 里。
最后使用cdev_add将字符设备usb_device_cdev添加到系统，并将USB_DEVICE_DEV(定义为 MKDEV(USB_DEVICE_MAJOR, 0)，即起始设备编号)放入cdev-> dev里, USB_DEVICE_MAX放入cdev->count里。
函数的最后又使用usb_register_notify注册了usb设备通知链。
2.7 usb_register_notify(&usbdev_nb)
usbdev_nb定义在 drivers/usb/core/devio.c：
static struct notifier_block usbdev_nb = {
.notifier_call = usbdev_notify,
};
usb_register_notify函数定义在drivers/usb/core/notify.c：
/**
* usb_register_notify - register a notifier callback whenever a usb change happens
* @nb: pointer to the notifier block for the callback events.
*
* These changes are either USB devices or busses being added or removed.
*/
void usb_register_notify(struct notifier_block *nb)
{
blocking_notifier_chain_register(&usb_notifier_list, nb);
}
usb通知链表头为usb_notifier_list:
static BLOCKING_NOTIFIER_HEAD(usb_notifier_list);
在drivers/usb/core/notify.c文件中,有四个函数对usb_notifier_list中发送通知，这四个函数如下:
void usb_notify_add_device(struct usb_device *udev)
{
blocking_notifier_call_chain(&usb_notifier_list, USB_DEVICE_ADD, udev);
}
void usb_notify_remove_device(struct usb_device *udev)
{
/* Protect against simultaneous usbfs open */
mutex_lock(&usbfs_mutex);
blocking_notifier_call_chain(&usb_notifier_list,
USB_DEVICE_REMOVE, udev);
mutex_unlock(&usbfs_mutex);
}
void usb_notify_add_bus(struct usb_bus *ubus)
{
blocking_notifier_call_chain(&usb_notifier_list, USB_BUS_ADD, ubus);
}
void usb_notify_remove_bus(struct usb_bus *ubus)
{
blocking_notifier_call_chain(&usb_notifier_list, USB_BUS_REMOVE, ubus);
}
当这些事件发生后会调用usbdev_nb指定的notifier_cal方法，即usbdev_notify：
static int usbdev_notify(struct notifier_block *self,
unsigned long action, void *dev)
{
switch (action) {
case USB_DEVICE_ADD: // 设备添加
break;
case USB_DEVICE_REMOVE: // 设备删除
usbdev_remove(dev);
break;
}
return NOTIFY_OK;
}
2.8 usb_hub_init()
int usb_hub_init(void)
{
if (usb_register(&hub_driver) < 0) {
printk(KERN_ERR "%s: can't register hub driver\n",
usbcore_name);
return -1;
}
/*
* The workqueue needs to be freezable to avoid interfering with
* USB-PERSIST port handover. Otherwise it might see that a full-speed
* device was gone before the EHCI controller had handed its port
* over to the companion full-speed controller.
*/
hub_wq = alloc_workqueue("usb_hub_wq", WQ_FREEZABLE, 0);
if (hub_wq)
return 0;
/* Fall through if kernel_thread failed */
usb_deregister(&hub_driver);
pr_err("%s: can't allocate workqueue for usb hub\n", usbcore_name);
return -1;
}
该函数主要做了以下工作：
- 通过usb_register向usb总线注册hub_driver接口驱动，指定了probe，disconnect，suspend，resume，id_table等相关函数。可以猜测，在根hub创建后，会执行此处的hub_probe函数。
- 创建新的工作队列，工作队列名称为usb_hub_wq，标志位为WQ_FREEZABLE；参数WQ＿FREEZABLE表示工作线程在挂起时候，需要先完成当前队列的所有工作之后才能挂起。创建好队列后，需要定义一个工作用于完成实际的任务。
hub_driver全局变量定义如下：
static struct usb_driver hub_driver = {
.name = "hub",
.probe = hub_probe,
.disconnect = hub_disconnect,
.suspend = hub_suspend,
.resume = hub_resume,
.reset_resume = hub_reset_resume,
.pre_reset = hub_pre_reset,
.post_reset = hub_post_reset,
.unlocked_ioctl = hub_ioctl,
.id_table = hub_id_table,
.supports_autosuspend = 1,
};
2.9 usb_register_device_drive(&usb_generic_driver, THIS_MODULE)
usb_register_device_driver函数用于注册通用设备驱动usb_generic_driver，usb_generic_driver定义在drivers/usb/core/generic.c：
struct usb_device_driver usb_generic_driver = {
.name = "usb",
.probe = generic_probe,
.disconnect = generic_disconnect,
#ifdef CONFIG_PM
.suspend = generic_suspend,
.resume = generic_resume,
#endif
.supports_autosuspend = 1,
};
所有的usb设备注册到usb总线后，都会和usb_generic_driver驱动匹配成功，也就是都会会执行generic_probe。
usb_register_device_driver定义在drivers/usb/core/driver.c文件中：
/**
* usb_register_device_driver - register a USB device (not interface) driver
* @new_udriver: USB operations for the device driver
* @owner: module owner of this driver.
*
* Registers a USB device driver with the USB core. The list of
* unattached devices will be rescanned whenever a new driver is
* added, allowing the new driver to attach to any recognized devices.
*
* Return: A negative error code on failure and 0 on success.
*/
int usb_register_device_driver(struct usb_device_driver *new_udriver,
struct module *owner)
{
int retval = 0;
if (usb_disabled())
return -ENODEV;
new_udriver->drvwrap.for_devices = 1;
new_udriver->drvwrap.driver.name = new_udriver->name;
new_udriver->drvwrap.driver.bus = &usb_bus_type;
new_udriver->drvwrap.driver.probe = usb_probe_device;
new_udriver->drvwrap.driver.remove = usb_unbind_device;
new_udriver->drvwrap.driver.owner = owner;
retval = driver_register(&new_udriver->drvwrap.driver);
if (!retval)
pr_info("%s: registered new device driver %s\n",
usbcore_name, new_udriver->name);
else
printk(KERN_ERR "%s: error %d registering device "
" driver %s\n",
usbcore_name, retval, new_udriver->name);
return retval;
}
这里首先初始化us设备口驱动里的驱动基类driver，然后调用driver_register进行驱动注册，关于驱动注册函数driver_register具体参考linux驱动移植-总线设备驱动。
这里简单介绍一下driver_register函数执行流程
- 将usb设备驱动添加到usb总线上；
- 遍历usb总线上的所有usb设备，然后进行usb设备驱动和usb设备的匹配；
- 匹配成功后最终会执行usb设备驱动的probe函数，过程中的驱动基类driver的probe函数和 usb_probe_device函数都是达到这个目的的中转函数而已。
3. usb接口驱动
3.1 usb接口驱动定义
在linux 设备模型中，usb接口驱动由usb_driver 结构表示，该结构体定义在 include/linux/usb.h文件中：
struct usb_driver {
const char *name;
int (*probe) (struct usb_interface *intf,
const struct usb_device_id *id);
void (*disconnect) (struct usb_interface *intf);
int (*unlocked_ioctl) (struct usb_interface *intf, unsigned int code,
void *buf);
int (*suspend) (struct usb_interface *intf, pm_message_t message);
int (*resume) (struct usb_interface *intf);
int (*reset_resume)(struct usb_interface *intf);
int (*pre_reset)(struct usb_interface *intf);
int (*post_reset)(struct usb_interface *intf);
const struct usb_device_id *id_table;
struct usb_dynids dynids;
struct usbdrv_wrap drvwrap;
unsigned int no_dynamic_id:1;
unsigned int supports_autosuspend:1;
unsigned int disable_hub_initiated_lpm:1;
unsigned int soft_unbind:1;
};
其中部分成员的含义如下：
- probe：当usb接口驱动和usb接口匹配成功之后，就会调用probe函数，usb接口驱动所有的资源的注册和初始化全部放在probe函数中；
- id_table：往往一个usb接口驱动可能能同时支持多个usb接口，这些usb接口的标识信息都放在该结构体数组中；
- drvwrap：为struct usbdrv_wrap结构体类型，其中有一个成员为struct device_driver类型，即驱动基类，驱动基类，内核维护的所有的驱动必须包含该成员；
usb_driver中的id_table在usb总线进行usb接口驱动和usb接口匹配时使用，id_table是一个数组，里面每个元素类型都是usb_device_id ，指定了满足某些规则的的usb接口会和usb接口驱动匹配，usb_device_id 结构定义在include/linux/mod_devicetable.h文件中：
struct usb_device_id {
/* which fields to match against? */
__u16 match_flags;
/* Used for product specific matches; range is inclusive */
__u16 idVendor;
__u16 idProduct;
__u16 bcdDevice_lo;
__u16 bcdDevice_hi;
/* Used for device class matches */
__u8 bDeviceClass;
__u8 bDeviceSubClass;
__u8 bDeviceProtocol;
/* Used for interface class matches */
__u8 bInterfaceClass;
__u8 bInterfaceSubClass;
__u8 bInterfaceProtocol;
/* Used for vendor-specific interface matches */
__u8 bInterfaceNumber;
/* not matched against */
kernel_ulong_t driver_info
__attribute__((aligned(sizeof(kernel_ulong_t))));
};
usb_driver成员drvwrap中成员driver是一个驱动基类，相当于驱动具有的最基础的属性，driver是struct device_driver类型，定义在include/linux/device.h文件中。
3.2 usb接口驱动注册
用usb_register宏向linux内核注册usb接口驱动，usb_register这个上面介绍了，不再重复介绍。
3.3 usb接口驱动卸载
用usb_deregister函数卸载usb接口驱动，函数定义在drivers/usb/core/driver.c文件中：
void usb_deregister(struct usb_driver *driver)
{
pr_info("%s: deregistering interface driver %s\n",
usbcore_name, driver->name);
usb_remove_newid_files(driver);
driver_unregister(&driver->drvwrap.driver);
usb_free_dynids(driver);
}
可以看到最终调用的driver_unregister，这里就不具体介绍了。
4. usb设备驱动
4.1 usb设备驱动定义
在linux 设备模型中，usb设备驱动由usb_device_driver 结构表示，该结构体定义在 include/linux/usb.h文件中：
struct usb_device_driver {
const char *name;
int (*probe) (struct usb_device *udev);
void (*disconnect) (struct usb_device *udev);
int (*suspend) (struct usb_device *udev, pm_message_t message);
int (*resume) (struct usb_device *udev, pm_message_t message);
struct usbdrv_wrap drvwrap;
unsigned int supports_autosuspend:1;
};
4.2 usb设备驱动注册
用usb_device_driver 结构体定义好usb设备驱动后，用usb_register_device_driver函数向linux内核注册usb设备驱动，usb_register_device_driver这个上面介绍了，不再重复介绍。
4.3 usb设备驱动卸载
用usb_deregister_device_driver函数卸载us设备口驱动，函数定义在drivers/usb/core/driver.c文件中：
void usb_deregister_device_driver(struct usb_device_driver *udriver)
{
pr_info("%s: deregistering device driver %s\n",
usbcore_name, udriver->name);
driver_unregister(&udriver->drvwrap.driver);
}
![[42000][923] ORA-00923: 未找到要求的 FROM 关键字](https://img-blog.csdnimg.cn/29265a741c2e4ca1bd057d527b2495d6.png)
