USB 结构

逻辑上的 USB 结构

对内核来讲， USB 总线也是一个设备， 内核中通过 usb_bus 来表示它 ，其定义如下：

struct usb_bus {      struct device *controller;  /* host/master side hardware */      int busnum;         /* Bus number (in order of reg) */      const char *bus_name;       /* stable id (PCI slot_name etc) */      u8 uses_dma;            /* Does the host controller use DMA? */      u8 uses_pio_for_control;    /*                       * Does the host controller use PIO                       * for control transfers?                       */      u8 otg_port;            /* 0, or number of OTG/HNP port */      unsigned is_b_host:1;       /* true during some HNP roleswitches */      unsigned b_hnp_enable:1;    /* OTG: did A-Host enable HNP? */      unsigned sg_tablesize;      /* 0 or largest number of sg list entries */        int devnum_next;        /* Next open device number in                       * round-robin allocation */        struct usb_devmap devmap;   /* device address allocation map */      struct usb_device *root_hub;    /* Root hub */      struct usb_bus *hs_companion;   /* Companion EHCI bus, if any */      struct list_head bus_list;  /* list of busses */        int bandwidth_allocated;    /* on this bus: how much of the time                       * reserved for periodic (intr/iso)                       * requests is used, on average?                       * Units: microseconds/frame.                       * Limits: Full/low speed reserve 90%,                       * while high speed reserves 80%.                       */      int bandwidth_int_reqs;     /* number of Interrupt requests */      int bandwidth_isoc_reqs;    /* number of Isoc. requests */    #ifdef CONFIG_USB_DEVICEFS      struct dentry *usbfs_dentry;    /* usbfs dentry entry for the bus */  #endif    #if defined(CONFIG_USB_MON) || defined(CONFIG_USB_MON_MODULE)      struct mon_bus *mon_bus;    /* non-null when associated */      int monitored;          /* non-zero when monitored */  #endif  };  

其中：

• busnum & bus_name:
  

  用于在全局中唯一标识该总线：前者为用于注册是使用的 Number ， 后者为描述性的字符串。

• controller:
  

  由于总线也是一个设备， usb_bus 中通过做为通用设备模型的 controller 来表明构成该总线的设备实例。

• bus_list:
  

  一个表头，用于将该 usb_bus 添加到全局的链表中，便于管理。

• root_hub:
  

  root_hub 实际上是一个虚拟出来的实例（参考第一小节），用于表示树形结构的根。

• devmap:
  

  一个 bitmap ， 用于记录该总线上已经分配了哪些 USB Number， 还有剩余。

内核中通过 usb_device 来表示一个 USB 设备，其定义如下：

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 connect_time;        unsigned do_remote_wakeup:1;      unsigned reset_resume:1;  #endif      struct wusb_dev *wusb_dev;      int slot_id;  };  

其中：

• devnum:
  

  Device Number， 该设备号为该设备在 USB 总线上的地址， 在整个 USB 树形结构中是全局唯一的。

• state & speed:
  

  表示设备的状态和速度，具体参考下面的定义：

  enum usb_device_speed {      USB_SPEED_UNKNOWN = 0,          /* enumerating */      USB_SPEED_LOW, USB_SPEED_FULL,      /* usb 1.1 */      USB_SPEED_HIGH,             /* usb 2.0 */      USB_SPEED_WIRELESS,         /* wireless (usb 2.5) */      USB_SPEED_SUPER,            /* usb 3.0 */  };    enum usb_device_state {      /* NOTATTACHED isn't in the USB spec, and this state acts       * the same as ATTACHED ... but it's clearer this way.       */      USB_STATE_NOTATTACHED = 0,        /* chapter 9 and authentication (wireless) device states */      USB_STATE_ATTACHED,      USB_STATE_POWERED,          /* wired */      USB_STATE_RECONNECTING,         /* auth */      USB_STATE_UNAUTHENTICATED,      /* auth */      USB_STATE_DEFAULT,          /* limited function */      USB_STATE_ADDRESS,      USB_STATE_CONFIGURED,           /* most functions */        USB_STATE_SUSPENDED        /* NOTE:  there are actually four different SUSPENDED       * states, returning to POWERED, DEFAULT, ADDRESS, or       * CONFIGURED respectively when SOF tokens flow again.       * At this level there's no difference between L1 and L2       * suspend states.  (L2 being original USB 1.1 suspend.)       */  };  

• devpath:
  

  表示了该设备在 USB 树形结构中的位置。

• parent:
  

  设备挂在的 hub 。

• bus:
  

  表明了该设备位于那个总线上。 usb_bus 的介绍在前面小节。

其他的成员变量，可以参考该结构定义之前的注释。

USB 设备驱动通过结构 usb_driver 来表示。 usb_driver 结构是 USB 设备与 USB 层之上的其他内核模块合作的起点， 其定义如下：

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 soft_unbind:1;  };  

其中：

• name
  

  驱动名字，全局唯一，一般用于管理用途。

• drvwrap
  

  该结构是 Linux 内核模型中通用驱动的一个包装，定义如下：

  struct usbdrv_wrap {      struct device_driver driver;      int for_devices;  };  

  其中，

  • driver 是通用驱动
  • for_devices 用于区分该驱动是接口驱动还是设备驱动：
    • for_devices = 0: 接口驱动
    • for_devices = 1: 设备驱动
• id_table
  

  与 pci_driver 类似， USB 设备驱动通过 id_table 来表明该驱动所能驱动的设备。

  其定义如下：

  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;        /* not matched against */      kernel_ulong_t  driver_info;  };  

  其中的 match_flags 是一个 flag ， 用于说明在确定某一设备是否该由该驱动进行管理时， 应该比较的成员变量。

• probe 与其他函数指针

  若干操作函数。其中， probe 会在为设备找到驱动或者为驱动找到了设备后调用。