usb描述符
在每个usb设备内部，同样也包含了类似于PCI配置寄存器这样的固定格式的数据，通过这些数据，usb主机就可以获取usb设备的类型，生产商等信息。这组固定的数据称为usb描述符。标准的usb设备有5种usb描述符：
设备描述符，配置描述符，接口描述符，端点描述符，字符串描述符。
一个设备只有一个设备描述符，而一个设备描述符可以包含多个配置描述符，一个配置描述符可以包含多个接口描述符，一个接口使用了几个端点，就有几个端点描述符。
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就像我们平时程序设计经常使用的方法一样，一个对象由一个结构体来表示，但还会再用来一个结构体来描述这个对象的一些属性。usb驱动框架也采用了这样的设计思想，usb框架中每一个组成部分都用两个结构体来描述：一个结构体表示成员组成，另一个结构体表示属性组成。Linux-USB核心定义了4个usb描述符。
- struct usb_device <---> struct usb_device_descriptor
- struct usb_host_config; <--> struct usb_config_descriptor
- struct usb_host_interface; <--> struct usb_interface_descriptor
- struct usb_host_endpoint; <--> struct usb_endpoint_descriptor
由此可见 struct usb_device的名称应该改为 struct usb_host_device
设备描述
linux内核使用struct usb_device来描述一个usb设备
struct usb_device
{
int devnum; usb设备号
char devpath [16]; 设备id字符串
enum usb_device_state state; 设备状态：未连接，已配置
enum usb_device_speed speed; 高速，全速，低速
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; usb设备描述符
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 discon_suspended: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];
int pm_usage_cnt;
u32 quirks;
atomic_t urbnum;
unsigned long active_duration;
#ifdef CONFIG_PM
struct delayed_work autosuspend;
struct work_struct autoresume;
struct mutex pm_mutex;
unsigned long last_busy;
int autosuspend_delay;
unsigned long connect_time;
unsigned auto_pm:1;
unsigned do_remote_wakeup:1;
unsigned reset_resume:1;
unsigned autosuspend_disabled:1;
unsigned autoresume_disabled:1;
unsigned skip_sys_resume:1;
#endif
struct wusb_dev *wusb_dev;
};
linux内核使用struct usb_device_descriptor来对应usb描述符中的设备描述符
/* USB_DT_DEVICE: Device descriptor */
struct usb_device_descriptor {
__u8 bLength;描述符长度，固定为0x12
__u8 bDescriptorType;设备描述符类型，固定为0x01
__le16 bcdUSB;规范发布号。表示本设备能适用哪种协议，如2.0=0200
__u8 bDeviceClass;类型代码
__u8 bDeviceSubClass;子类型代码
__u8 bDeviceProtocol;协议代码
__u8 bMaxPacketSize0;端点0最大分组大小
__le16 idVendor;供应商ID
__le16 idProduct;产品ID，由厂家自行设置
__le16 bcdDevice;设备出厂编码，由厂家自行设置
__u8 iManufacturer;厂商描述符字符串索引，索引到对应的字符串描述符。为0表示没有。
__u8 iProduct;产品描述符字符串索引
__u8 iSerialNumber;设备序列号字符串索引
__u8 bNumConfigurations;可能的配置数。
} __attribute__ ((packed)); 按字节对齐
上面的这个结构是根据usb协议而来的
Table 9-8. Standard Device Descriptor
配置描述
linux内核使用struct usb_host_config来描述一个usb配置：
struct usb_host_config{
struct usb_config_descriptor desc; 配置描述符
char *string; /* iConfiguration string, if present */配置的字符串（如果存在）
/* List of any Interface Association Descriptors in this
* configuration. */
struct usb_interface_assoc_descriptor *intf_assoc[USB_MAXIADS];
/* the interfaces associated with this configuration,
* stored in no particular order */
struct usb_interface *interface[USB_MAXINTERFACES];接口链表
/* Interface information available even when this is not the
* active configuration */
struct usb_interface_cache *intf_cache[USB_MAXINTERFACES];
unsigned char *extra; /* Extra descriptors */
int extralen;
};
配置描述
linux内核使用struct usb_config_descriptor来对应usb描述符中的配置描述符
struct usb_config_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__le16 wTotalLength;
__u8 bNumInterfaces;
__u8 bConfigurationValue;
__u8 iConfiguration;
__u8 bmAttributes;
__u8 bMaxPower;
} __attribute__ ((packed));
上面的这个结构是根据usb协议而来的
Table 9-10. Standard Configuration Descriptor
接口描述
linux 内核使用struct usb_interface来描述usb接口。
struct usb_interface
{
/* array of alternate settings for this interface,
* stored in no particular order */
struct usb_host_interface *altsetting; 接口设置数组
struct usb_host_interface *cur_altsetting; /* the currently当前设置
* active alternate setting */
unsigned num_altsetting; /* number of alternate settings */设置数
/* 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 is_active:1; /* the interface is not suspended */
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;
struct device dev; /* interface specific device info */
struct device *usb_dev;
int pm_usage_cnt; /* usage counter for autosuspend */
struct work_struct reset_ws; /* for resets in atomic context */
};
一个配置包含一个或多个接口，一个接口包含一个或多个设置
struct usb_host_interface {
struct usb_interface_descriptor desc;接口描述符
/* array of desc.bNumEndpoint endpoints associated with this
* interface setting. these will be in no particular order.
*/
struct usb_host_endpoint *endpoint;接口包含的端点不包含0号端点，它是控制端点。
char *string; /* iInterface string, if present */
unsigned char *extra; /* Extra descriptors */
int extralen;
};
接口描述
struct usb_interface_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__u8 bInterfaceNumber;
__u8 bAlternateSetting;
__u8 bNumEndpoints;接口包含的端点个数，不包含0号端点，它是控制端点。
__u8 bInterfaceClass;
__u8 bInterfaceSubClass;
__u8 bInterfaceProtocol;
__u8 iInterface;
} __attribute__ ((packed));
上面的这个结构是根据usb协议而来的
Table 9-12. Standard Interface Descriptor
端点描述
struct usb_host_endpoint {
struct usb_endpoint_descriptor desc;端点描述符
struct list_head urb_list;
void *hcpriv;
struct ep_device *ep_dev; /* For sysfs info */
unsigned char *extra; /* Extra descriptors */
int extralen;
int enabled;
};
端点描述
struct usb_endpoint_descriptor
{
__u8 bLength;
__u8 bDescriptorType;
__u8 bEndpointAddress;
__u8 bmAttributes;
__le16 wMaxPacketSize;
__u8 bInterval;
/* NOTE: these two are _only_ in audio endpoints. */
/* use USB_DT_ENDPOINT*_SIZE in bLength, not sizeof. */
__u8 bRefresh;
__u8 bSynchAddress;
} __attribute__ ((packed));
Table 9-13. Standard Endpoint Descriptor
struct _STRING_DEscriptOR_STRUCT
{
BYTE bLength; //设备描述符的字节数大小，为0x12
BYTE bDescriptorType; //描述符类型编号，为0x01
BYTE SomeDescriptor[36]; //UNICODE编码的字符串
}