linux usb 设备驱动和接口驱动

http://blog.chinaunix.net/uid-9185047-id-445204.html

2011-04-11

每个usb设备，都可能会有多个接口，每个接口都实现了一个功能。

在linux上，每个usb设备是一个device，而每个接口也同样是一个device。

所有的usb设备的所对应的驱动是同一个驱动

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,

};

但是每一个接口所对应的驱动则是单独的驱动。

我们看一下usb设备和usb接口的定义。如下：

struct usb_device {

int devnum;

char devpath[16];

u32 route;

enum usb_device_state state;

enum usb_device_speed speed;

struct usb_tt *tt;

int ttport;

unsigned int toggle[2];

struct usb_device *parent;

struct usb_bus *bus;

struct usb_host_endpoint ep0;

struct device dev;

struct usb_device_descriptor descriptor;

struct usb_host_config *config;

struct usb_host_config *actconfig;

struct usb_host_endpoint *ep_in[16];

struct usb_host_endpoint *ep_out[16];

char **rawdescriptors;

unsigned short bus_mA;

u8 portnum;

u8 level;

unsigned can_submit:1;

unsigned persist_enabled:1;

unsigned have_langid:1;

unsigned authorized:1;

unsigned authenticated:1;

unsigned wusb:1;

int string_langid;

/* static strings from the device */

char *product;

char *manufacturer;

char *serial;

struct list_head filelist;

#ifdef CONFIG_USB_DEVICE_CLASS

struct device *usb_classdev;

#endif

#ifdef CONFIG_USB_DEVICEFS

struct dentry *usbfs_dentry;

#endif

int maxchild;

struct usb_device *children[USB_MAXCHILDREN];

u32 quirks;

atomic_t urbnum;

unsigned long active_duration;

#ifdef CONFIG_PM

unsigned long last_busy;

int autosuspend_delay;

unsigned long connect_time;

unsigned do_remote_wakeup:1;

unsigned reset_resume:1;

#endif

struct wusb_dev *wusb_dev;

int slot_id;

};

struct usb_interface {

/* array of alternate settings for this interface,

* stored in no particular order */

struct usb_host_interface *altsetting;

struct usb_host_interface *cur_altsetting; /* the currently

* active alternate setting */

unsigned num_altsetting; /* number of alternate settings */

/* If there is an interface association descriptor then it will list

* the associated interfaces */

struct usb_interface_assoc_descriptor *intf_assoc;

int minor; /* minor number this interface is

* bound to */

enum usb_interface_condition condition; /* state of binding */

unsigned sysfs_files_created:1; /* the sysfs attributes exist */

unsigned ep_devs_created:1; /* endpoint "devices" exist */

unsigned unregistering:1; /* unregistration is in progress */

unsigned needs_remote_wakeup:1; /* driver requires remote wakeup */

unsigned needs_altsetting0:1; /* switch to altsetting 0 is pending */

unsigned needs_binding:1; /* needs delayed unbind/rebind */

unsigned reset_running:1;

unsigned resetting_device:1; /* true: bandwidth alloc after reset */

struct device dev; /* interface specific device info */

struct device *usb_dev;

atomic_t pm_usage_cnt; /* usage counter for autosuspend */

struct work_struct reset_ws; /* for resets in atomic context */

};

我们可以看到，这两个定义里都有struct device。

不管是USB设备还是USB接口，都会被注册到同一个bus上，也就是usb_bus_type，其之间的区别会在match函数中区分，之后再去绑定不同的driver。

当一个USB设备被插入的时候，USB设备驱动，也就是usb_generic_driver会跟USB设备交互，得到其所有的各种描述符，并为每个接口都定义成为一个device，之后再加载到usb_bus上，让其去匹配其对应的接口驱动程序。