Linux设备驱动之usb设备驱动详解

1.Linux usb设备驱动框架

USB是通用串行总线的总称，Linux内核几乎支持所有的usb设备，包括键盘，鼠标，打印机，modem,扫描仪。Linux的usb驱动分为主机驱动与gadget驱动。前者是设备连接到计算机上，通过主机驱动扫描usb设备，控制所连接的设备。而gadget驱动一般用于嵌入式设备，gadget驱动用于控制嵌入式设备。Linux的usb驱动两种类型图如下:

 

 

 

 

 

左侧是usb的主机驱动，右侧是gadget驱动。下面着重介绍一下usb的主机驱动:

(1)usb主机控制器-直接与硬件设备交互。

(2)usb core-向usb设备驱动提供API以及usb主机控制器驱动的程序。使用usb core所提供的函数，宏来完成数据处理的功能。

(3)usb设备驱动，即usb接口驱动，一般所说的usb驱动指的是usb接口驱动

 

 

 

 

2.usb系统的组成部分

usb系统一般由三个部分组成，主机，一个或多个usb hub,以及与之些hub连接的usb设备。

(1)主机

在任何的usb系统中仅有一个主机，主机系统中的usb接口即上图中的主机控制器，主机控制器可由硬件，软件或固件组成。主机主要负责:

a.检测usb设备的连接与拆除

b.管理主机与usb设备之间的控制流

c.管理主机与usb设备之间的数据流

d.收集状态和活动的统计

e.为连接的usb设备提供电源

 

 

(2)usb设备

所有的usb设备都是通过地址来存取的，这个地址在连接或枚举时分配。usb设备对usb系统来说是端点的集合，一组端点实现一个接口。设备端点是usb设备中唯一可寻址的部分。它是主机与设备之间通信流的结束点。一系列的相互独立的端点构成了usb逻辑设备。每个端点支持流进设备或者是流出设备。

主机与设备端点上的usb数据传输是通过管道的方式。

 

(3)hub

所有的usb device都连接在hub端口上。

 

 

 

3. usb传输模式

 

(1)控制传输模式(Control)

控制传输模式支持双向传输，用来处理从usb主机端口到usb设备端口的数据传输，用于控制指令，设备状态查询以及确认命令。

 

(2)等时传输方式(lsochronous )

等时传输是一种周期性的连续性的意向传输模式，通常用于对时间有着密切关系的信息的传输，对准确性要求不高，但对时间要求极为敏感的设备，如视频，音频的传输。

 

(3)中断传输模式(Interrupt)

中断传输模式用于非周期性的，自然发生的，数据量小的传输，数据传输的方向是从设备到主机。如usb键盘和鼠标

 

(4)批量传输模式(bulk)

批量传输模式是一种单向的，用于大量数据传输的模式，该方式用来传输正确无误的数据。通常打印机，扫描仪，数码相机以这种方式与主机连接

 

 

4. usb设备组成

(1)一个usb设备由可以有一个或多个配置

(2)一个配置通常可以有一个或多个接口

(3)一个接口通常可以有一个或多个端点

通常所尽的usb设备驱动是指接口驱动，即一个接口对应一个驱动。

所以Linux usb设备有四大描述符，分别为设备描述符，配置描述符，接口描述符，端点描述符。下面看一个这几个描述符的相关数据结构:

 

 

struct usb_device_descriptor

{
      _u8 bLength;  //此描述符的字节数
      _u8  bDescriptorType; //描述符的种类为设备
      _u16 bcdUSB;  //此设备与描述符兼容的usb设备说明版本号(BCD码)
      _u8   bDeviceClass; //设备类码
      _u8   bDeviceSubClass; //设备子类码
      _u8   bDeviceProtocol; //协议码
      _u8   bMaxPacketSize0; //端点0的最大包大小
      _u16 idVendor; //厂商标志
      _u16  idProduct; //产品标志
      _u16 bcdDevice; //设备发行号
      _u8   iManufacturer; //描述厂商的字串索引

      _u8   iProduct; //描述产品信息的字串索引

      _u8  iSerialNumber; //描述设备序列号信息的字串索引
      _u8  bNumConfigurations;//此设备支持的配置数

  }_attribute_ ((packed));

 

设备类码的典型值如下:

 

#define USB_CLASS_PER_INTERFACE 0

#define USB_CLAS_AUDIO 1     //声音设备

#define USB_CLASS_COMM 2   // 调制解调器，网卡，ISDN连接

#define USB_CLASS_HID  3    //HID设备，如鼠标，键盘

#define USB_CLASS_PHYSICAL 5 //物理设备

#define USB_CLASS_STILL_IMAGE 6 //静止图像捕捉设备

#define USB_CLASS_PRINTER 7//打印机

#define USB_CLASS_MASS_STORAGE //8 批量存储设备

#define USB_CLASS_HUB 9   //USB HUBS

#define USB_CLASS_CSCID 0x0B  //智能卡

#define USB_CLASS_VIDEO 0X0E //视频设备，如网络摄像头

#define USB_CLASS_VENDOR_SPEC 0xFF //厂商自定义的设备

 

  struct usb_config_descriptor{

 

 _u8 bLength ;//此描述符的字节数

_u8 bDescriptorType; //配置描述符类型

_u16 wTotalLength; //此配置信息的总长(包括配置，接口，端点和设备类型及厂商定义的描述符)

_u8 bNumInterfaces; //此配置所支持的接口数

_u8 bConfigurationValue ;//在setConfiguration()请求中用作参数来选定此配置

_u8 iConfiguration; //描述此配置的字串描述符索引

_u8 bmAttributes; //电源配置特性

_u8 bMaxpowe;r //此配置下的总线电源耗电量

}_attribute_ ((packed));

 

 

配置描述符给出了usb设备配置信息，以及此配置下的接口数。每个接口可能的独立操作。

 

 

 

struct usb_interface_descriptor{

 

_u8 bLength ;//此描述符的字节数

_u8 bDescriptorType;//接口描述符类

_u8 bInterfacNumber;//接口号，当前配置所支持的接口数组索引,从0开始

_u8 bNumEndpoints ;//此接口用的端点数量，如果是0,说明此接口只有缺省控制通道

_u8 bAlernateSetting;//可选设备的索引值

_u8 bInterfaceClass;// 类值,0值作为将来保留使用如果是0FFH,此接口由厂商说明

_u8 bInterfaceSubClass;//子类码

_u8 bInterfaceProtocol;//协议码

_u8 iInterface;//描述此接口的字串描述符索引

 

}_attribute_ ((packed));

 

struct usb_endpoint_descriptor{

_u8 bLength ;//此描述符的字节数

_u8 bDescriptorType;//端点描述符类

_u8 bEndpointAddress;此描述符所描述的端点的地址

_u8 bmAtrributes;//所指定的端点的特性，如果是00=控制传送,01=等时传送,10=批传送,11=中断传送

_u8 wMaxPacketSize;//当前配置下端点能够发送与接收的最大数据包大小

_u8 bInterval;//轮询数据传送端点的时间间隙

_u8 bRefresh

_u8 bSynchAddress

}_attribute_ ((packed));

 

以上给出了usb中的设备描述符，配置描述符，接口描述符和端点描述符。

 

 

5. usb设备驱动的几个重要的数据结构

 

usb_driver,usb_device,usb_bus.

 

 

/** 
788 * stru ct usb_driver - identifies U SB interface driver to u sbcore 
789 * @name: The driver name shou ld be u niqu e among U SB drivers, 
790 *      and shou ld normally be the same as the modu le name. 
791 * @probe: Called to see if the driver is willing to manage a particu lar 
792 *      interface on a device.  If it is, probe retu rns zero and u ses 
793 *      u sb_set_intfdata() to associate driver-specific data with the 
794 *      interface.  It may also u se u sb_set_interface() to specify the 
795 *      appropriate altsetting.  If u nwilling to manage the interface, 
796 *      retu rn -ENODEV, if genu ine IO errors occu red, an appropriate 
797 *      negative errno valu e. 
798 * @disconnect: Called when the interface is no longer accessible, u su ally 
799 *      becau se its device has been (or is being) disconnected or the 
800 *      driver modu le is being u nloaded. 
801 * @u nlocked_ioctl: U sed for drivers that want to talk to u serspace throu gh 
802 *      the "u sbfs" filesystem.  This lets devices provide ways to 
803 *      expose information to u ser space regardless of where they 
804 *      do (or don't) show u p otherwise in the filesystem. 
805 * @su spend: Called when the device is going to be su spended by the system. 
806 * @resu me: Called when the device is being resu med by the system. 
807 * @reset_resu me: Called when the su spended device has been reset instead 
808 *      of being resu med. 
809 * @pre_reset: Called by u sb_reset_device() when the device 
810 *      is abou t to be reset. 
811 * @post_reset: Called by u sb_reset_device() after the device 
812 *      has been reset 
813 * @id_table: U SB drivers u se ID table to su pport hotplu gging. 
814 *      Export this with MODU LE_DEVICE_TABLE(u sb,...).  This mu st be set 
815 *      or you r driver's probe fu nction will never get called. 
816 * @dynids: u sed internally to hold the list of dynamically added device 
817 *      ids for this driver. 
818 * @drvwrap: Driver-model core stru ctu re wrapper. 
819 * @no_dynamic_id: if set to 1, the U SB core will not allow dynamic ids to be 
820 *      added to this driver by preventing the sysfs file from being created. 
821 * @su pports_au tosu spend: if set to 0, the U SB core will not allow au tosu spend 
822 *      for interfaces bou nd to this driver. 
823 * @soft_u nbind: if set to 1, the U SB core will not kill U RBs and disable 
824 *      endpoints before calling the driver's disconnect method. 
825 * 
826 * U SB interface drivers mu st provide a name, probe() and disconnect() 
827 * methods, and an id_table.  Other driver fields are optional. 
828 * 
829 * The id_table is u sed in hotplu gging.  It holds a set of descriptors, 
830 * and specialized data may be associated with each entry.  That table 
831 * is u sed by both u ser and kernel mode hotplu gging su pport. 
832 * 
833 * The probe() and disconnect() methods are called in a context where 
834 * they can sleep, bu t they shou ld avoid abu sing the privilege.  Most 
835 * work to connect to a device shou ld be done when the device is opened, 
836 * and u ndone at the last close.  The disconnect code needs to address 
837 * concu rrency issu es with respect to open() and close() methods, as 
838 * well as forcing all pending I/O requ ests to complete (by u nlinking 
839 * them as necessary, and blocking u ntil the u nlinks complete). 
840 */ 
841 stru ct usb_driver {
842          const char *name ;
843 
844          int (*probe ) (stru ct u sb_interface *intf ,
845                        const stru ct u sb_device_id *id );
846 
847          void (*disconnect ) (stru ct u sb_interface *intf );
848 
849          int (*u nlocked_ioctl) (stru ct u sb_interface *intf , u nsigned int code ,
850                          void *bu f );
851 
852          int (*su spend ) (stru ct u sb_interface *intf , pm_message_t message );
853          int (*resu me ) (stru ct u sb_interface *intf );
854          int (*reset_resu me)(stru ct u sb_interface *intf );
855 
856          int (*pre_reset )(stru ct u sb_interface *intf );
857          int (*post_reset)(stru ct u sb_interface *intf );
858 
859          const stru ct u sb_device_id *id_table ;
860 
861          stru ct u sb_dynids dynids;
862          stru ct u sbdrv_wrap drvwrap;
863          u nsigned int no_dynamic_id:1;
864          u nsigned int su pports_au tosu spend:1;
865          u nsigned int soft_u nbind:1;
866 };

 

usb_driver中的probe函数扫描连接到主机上的usb设备，并且注册usb接口驱动。

 

disconnect函数是当usb设备移除时调用。

 

 

/* 
310 * Allocated per bu s (tree of devices) we have: 
311 */ 
312 stru ct u sb_bu s {
313          stru ct device *controller ;      /* host/master side hardware */ 
314          int bu snu m;                     /* Bu s nu mber (in order of reg) */ 
315          const char *bu s_name;           /* stable id (PCI slot_name etc) */ 
316          u 8 u ses_dma;                    /* Does the host controller u se DMA? */ 
317          u 8 u ses_pio_for_control;        /* 
318                                          * Does the host controller u se PIO 
319                                          * for control transfers? 
320                                          */ 
321          u 8 otg_port;                    /* 0, or nu mber of OTG/HNP port */ 
322          u nsigned is_b_host:1;           /* tru e du ring some HNP roleswitches */ 
323          u nsigned b_hnp_enable:1;        /* OTG: did A-Host enable HNP? */ 
324          u nsigned sg_tablesize ;          /* 0 or largest nu mber of sg list entries */ 
325 
326          int devnu m_next;                /* Next open device nu mber in 
327                                          * rou nd-robin allocation */ 
328 
329          stru ct u sb_devmap  devmap;       /* device address allocation map */ 
330          stru ct usb_device * root_hu b;    /* Root hu b */ 
331          stru ct u sb_bu s *hs_companion;   /* Companion EHCI bu s, if any */ 
332          stru ct list_head bu s_list;      /* list of bu sses */ 
333 
334          int bandwidth_allocated;        /* on this bu s: how mu ch of the time 
335                                          * reserved for periodic (intr/iso) 
336                                          * requ ests is u sed, on average? 
337                                          * U nits: microseconds/frame. 
338                                          * Limits: Fu ll/low speed reserve 90%, 
339                                          * while high speed reserves 80%. 
340                                          */ 
341          int bandwidth_int_reqs;         /* nu mber of Interru pt requ ests */ 
342          int bandwidth_isoc_reqs;        /* nu mber of Isoc. requ ests */ 
343 
344 #ifdef CONFIG_USB_DEVICE FS
345          stru ct dentry *u sbfs_dentry;    /* u sbfs dentry entry for the bu s */ 
346 #endif
347 
348 #if defined (CONFIG_U SB_MON) || defined (CONFIG_U SB_MON_MODU LE)
349          stru ct mon_bu s *mon_bu s ;        /* non-nu ll when associated */ 
350          int monitored;                  /* non-zero when monitored */ 
351 #endif
352 };
353

 

 

** 
370 * stru ct usb_device - kernel's representation of a U SB device 
371 * @devnu m: device nu mber; address on a U SB bu s 
372 * @devpath: device ID string for u se in messages (e.g., /port/...) 
373 * @rou te: tree topology hex string for u se with xHCI 
374 * @state: device state: configu red, not attached, etc. 
375 * @speed: device speed: high/fu ll/low (or error) 
376 * @tt: Transaction Translator info; u sed with low/fu ll speed dev, highspeed hu b 
377 * @ttport: device port on that tt hu b 
378 * @toggle: one bit for each endpoint, with ([0] = IN, [1] = OU T) endpoints 
379 * @parent: ou r hu b, u nless we're the root 
380 * @bu s: bu s we're part of 
381 * @ep0: endpoint 0 data (defau lt control pipe) 
382 * @dev: generic device interface 
383 * @descriptor: U SB device descriptor 
384 * @config: all of the device's configs 
385 * @actconfig: the active configu ration 
386 * @ep_in: array of IN endpoints 
387 * @ep_ou t: array of OU T endpoints 
388 * @rawdescriptors: raw descriptors for each config 
389 * @bu s_mA: Cu rrent available from the bu s 
390 * @portnu m: parent port nu mber (origin 1) 
391 * @level: nu mber of U SB hu b ancestors 
392 * @can_su bmit: U RBs may be su bmitted 
393 * @persist_enabled:  U SB_PERSIST enabled for this device 
394 * @have_langid: whether string_langid is valid 
395 * @au thorized: policy has said we can u se it; 
396 *      (u ser space) policy determines if we au thorize this device to be 
397 *      u sed or not. By defau lt, wired U SB devices are au thorized. 
398 *      WU SB devices are not, u ntil we au thorize them from u ser space. 
399 *      FIXME -- complete doc 
400 * @au thenticated: Crypto au thentication passed 
401 * @wu sb: device is Wireless U SB 
402 * @string_langid: langu age ID for strings 
403 * @produ ct: iProdu ct string, if present (static) 
404 * @manu factu rer: iManu factu rer string, if present (static) 
405 * @serial: iSerialNu mber string, if present (static) 
406 * @filelist: u sbfs files that are open to this device 
407 * @u sb_classdev: U SB class device that was created for u sbfs device 
408 *      access from u serspace 
409 * @u sbfs_dentry: u sbfs dentry entry for the device 
410 * @maxchild: nu mber of ports if hu b 
411 * @children: child devices - U SB devices that are attached to this hu b 
412 * @qu irks: qu irks of the whole device 
413 * @u rbnu m: nu mber of U RBs su bmitted for the whole device 
414 * @active_du ration: total time device is not su spended 
415 * @connect_time: time device was first connected 
416 * @do_remote_wakeu p:  remote wakeu p shou ld be enabled 
417 * @reset_resu me: needs reset instead of resu me 
418 * @wu sb_dev: if this is a Wireless U SB device, link to the WU SB 
419 *      specific data for the device. 
420 * @slot_id: Slot ID assigned by xHCI 
421 * 
422 * Notes: 
423 * U sbcore drivers shou ld not set u sbdev->state directly.  Instead u se 
424 * u sb_set_device_state(). 
425 */ 
426 stru ct usb_device {
427          int             devnu m;
428          char            devpath[16];
429          u 32              rou te;
430          enu m usb_device _state    state ;
431          enu m usb_device _speed    speed ;
432 
433          stru ct u sb_tt    *tt;
434          int             ttport;
435 
436          u nsigned int toggle [2];
437 
438          stru ct usb_device *parent ;
439          stru ct u sb_bu s *bu s ;
440          stru ct u sb_host_endpoint ep0;
441 
442          stru ct device dev ;
443 
444          stru ct usb_device _descriptor descriptor ;
445          stru ct u sb_host_config *config ;
446 
447          stru ct u sb_host_config *actconfig;
448          stru ct u sb_host_endpoint *ep_in[16];
449          stru ct u sb_host_endpoint *ep_ou t[16];
450 
451          char **rawdescriptors;
452 
453          u nsigned short bu s_mA;
454          u 8 portnu m;
455          u 8 level;
456 
457          u nsigned can_su bmit:1;
458          u nsigned persist_enabled:1;
459          u nsigned have_langid:1;
460          u nsigned au thorized:1;
461          u nsigned au thenticated:1;
462          u nsigned wu sb:1;
463          int string_langid;
464 
465          /* static strings from the device */ 
466          char *produ ct ;
467          char *manu factu rer ;
468          char *serial ;
469 
470          stru ct list_head filelist;
471 #ifdef CONFIG_USB_DEVICE _CLASS
472          stru ct device *u sb_classdev;
473 #endif
474 #ifdef CONFIG_USB_DEVICE FS
475          stru ct dentry *u sbfs_dentry;
476 #endif
477 
478          int maxchild;
479          stru ct usb_device *children[U SB_MAXCHILDREN ];
480 
481          u 32 qu irks ;
482          atomic_t u rbnu m;
483 
484          u nsigned long active_du ration;
485 
486 #ifdef CONFIG_PM 
487          u nsigned long connect_time;
488 
489          u nsigned do_remote_wakeu p:1;
490          u nsigned reset_resu me:1;
491 #endif
492          stru ct wu sb_dev *wu sb_dev ;
493          int slot_id;
494 };
495 #define to_usb_device (d ) container_of (d , stru ct usb_device , dev )
496 
497 static inline stru ct usb_device *interface_to_u sbdev (stru ct u sb_interface *intf )
498 {
499          retu rn to_usb_device (intf ->dev .parent );
500 }
501

 

以上三个结构体分别是usb_driver,usb_bus,usb_device设备结构体。

 

 

 

usb_interface结构体:

 

struct usb_interface {
160          /* array of alternate settings for this interface, 
161          * stored in no particular order */ 
162          struct usb_host_interface *altsetting ;
163 
164          struct usb_host_interface *cur_altsetting;      /* the currently 
165                                          * active alternate setting */ 
166          unsigned num_altsetting;        /* number of alternate settings */ 
167 
168          /* If there is an interface association descriptor then it will list 
169          * the associated interfaces */ 
170          struct usb_interface_assoc_descriptor *intf_assoc;
171 
172          int minor ;                      /* minor number this interface is 
173                                          * bound to */ 
174          enum usb_interface_condition condition;         /* state of binding */ 
175          unsigned sysfs_files_created:1; /* the sysfs attributes exist */ 
176          unsigned ep_devs_created:1;     /* endpoint "devices" exist */ 
177          unsigned unregistering:1;       /* unregistration is in progress */ 
178          unsigned needs_remote_wakeup:1; /* driver requires remote wakeup */ 
179          unsigned needs_altsetting0:1;   /* switch to altsetting 0 is pending */ 
180          unsigned needs_binding:1;       /* needs delayed unbind/rebind */ 
181          unsigned reset_running:1;
182          unsigned resetting_device:1;    /* true: bandwidth alloc after reset */ 
183 
184          struct device dev ;              /* interface specific device info */ 
185          struct device *usb_dev ;
186          atomic_t pm_usage_cnt;          /* usage counter for autosuspend */ 
187          struct work_struct reset_ws;    /* for resets in atomic context */ 
188 };

 struct usb_host_interface *altsetting包含了usb interface的所有可选设置。

 struct usb_host _interface *cur_altsetting是usb interface的当前可选设置。

 

下面看一个struct usb_host_interface

 

 

/* host-side wrapper for one interface setting's parsed descriptors */ 
77 stru ct usb_host_interface {
78          stru ct u sb_interface_descriptor desc ;
79 
80          /* array of desc.bNu mEndpoint endpoints associated with this 
81          * interface setting.  these will be in no particu lar order. 
82          */ 
83          stru ct u sb_host_endpoint *endpoint ;
84 
85          char *string ;           /* iInterface string, if present */ 
86          u nsigned char *extra;   /* Extra descriptors */ 
87          int extralen;
88 };

 

其中struct usb_interface_descriptor即是usb接口描述符。

struct usb_host_endpoint代表的是设备端点。

可以在desc中改变接口包含的端点数。

 

接下来看一下usb_host_endpoint这个结构体:

 

/** 
50 * stru ct usb_host_endpoint - host-side endpoint descriptor and qu eu e 
51 * @desc: descriptor for this endpoint, wMaxPacketSize in native byteorder 
52 * @ss_ep_comp: Su perSpeed companion descriptor for this endpoint 
53 * @u rb_list: u rbs qu eu ed to this endpoint; maintained by u sbcore 
54 * @hcpriv: for u se by HCD; typically holds hardware dma qu eu e head (QH) 
55 *      with one or more transfer descriptors (TDs) per u rb 
56 * @ep_dev: ep_device for sysfs info 
57 * @extra: descriptors following this endpoint in the configu ration 
58 * @extralen: how many bytes of "extra" are valid 
59 * @enabled: U RBs may be su bmitted to this endpoint 
60 * 
61 * U SB requ ests are always qu eu ed to a given endpoint, identified by a 
62 * descriptor within an active interface in a given U SB configu ration. 
63 */ 
64 stru ct usb_host_endpoint {
65          stru ct u sb_endpoint_descriptor           desc ;
66          stru ct u sb_ss_ep_comp_descriptor        ss_ep_comp;
67          stru ct list_head               u rb_list ;
68          void                            *hcpriv;
69          stru ct ep_device              *ep_dev;        /* For sysfs info */ 
70 
71          u nsigned char *extra;   /* Extra descriptors */ 
72          int extralen;
73          int enabled ;
74 };

 

 

其中struct usb_endpoint_descriptor是端点描述符。

 

 

urb(usb reqeust block):

urb主要用于Linux host与设备进行数据传输.

 

urb的生命周期:

(1)由usb设备驱动创建

(2)分配到usb设备的指定端点

(3)由Usb设备驱动提交到usb core

(4)由Usb core提交到usb 主机控制器

(5)由Usb主机控制器控制设备进行数据传输

(6)当urb完成的时候，usb主机控制器驱动通知usb 设备驱动

 

 

 

 

/** 
1006 * stru ct urb - U SB Requ est Block 
1007 * @urb _list: For u se by cu rrent owner of the URB . 
1008 * @anchor_list: membership in the list of an anchor 
1009 * @anchor: to anchor URB s to a common mooring 
1010 * @ep: Points to the endpoint's data stru ctu re.  Will eventu ally 
1011 *      replace @pipe. 
1012 * @pipe: Holds endpoint nu mber, direction, type, and more. 
1013 *      Create these valu es with the eight macros available; 
1014 *      u sb_{snd,rcv}TYPEpipe(dev,endpoint), where the TYPE is "ctrl" 
1015 *      (control), "bu lk", "int" (interru pt), or "iso" (isochronou s). 
1016 *      For example u sb_sndbu lkpipe() or u sb_rcvintpipe().  Endpoint 
1017 *      nu mbers range from zero to fifteen.  Note that "in" endpoint two 
1018 *      is a different endpoint (and pipe) from "ou t" endpoint two. 
1019 *      The cu rrent configu ration controls the existence, type, and 
1020 *      maximu m packet size of any given endpoint. 
1021 * @stream_id: the endpoint's stream ID for bu lk streams 
1022 * @dev: Identifies the U SB device to perform the requ est. 
1023 * @statu s: This is read in non-iso completion fu nctions to get the 
1024 *      statu s of the particu lar requ est.  ISO requ ests only u se it 
1025 *      to tell whether the URB was u nlinked; detailed statu s for 
1026 *      each frame is in the fields of the iso_frame-desc. 
1027 * @transfer_flags: A variety of flags may be u sed to affect how URB 
1028 *      su bmission, u nlinking, or operation are handled.  Different 
1029 *      kinds of URB can u se different flags. 
1030 * @transfer_bu ffer:  This identifies the bu ffer to (or from) which the I/O 
1031 *      requ est will be performed u nless URB _NO_TRANSFER_DMA_MAP is set 
1032 *      (however, do not leave garbage in transfer_bu ffer even then). 
1033 *      This bu ffer mu st be su itable for DMA; allocate it with 
1034 *      kmalloc() or equ ivalent.  For transfers to "in" endpoints, contents 
1035 *      of this bu ffer will be modified.  This bu ffer is u sed for the data 
1036 *      stage of control transfers. 
1037 * @transfer_dma: When transfer_flags inclu des URB _NO_TRANSFER_DMA_MAP, 
1038 *      the device driver is saying that it provided this DMA address, 
1039 *      which the host controller driver shou ld u se in preference to the 
1040 *      transfer_bu ffer. 
1041 * @sg: scatter gather bu ffer list 
1042 * @nu m_sgs: nu mber of entries in the sg list 
1043 * @transfer_bu ffer_length: How big is transfer_bu ffer.  The transfer may 
1044 *      be broken u p into chu nks according to the cu rrent maximu m packet 
1045 *      size for the endpoint, which is a fu nction of the configu ration 
1046 *      and is encoded in the pipe.  When the length is zero, neither 
1047 *      transfer_bu ffer nor transfer_dma is u sed. 
1048 * @actu al_length: This is read in non-iso completion fu nctions, and 
1049 *      it tells how many bytes (ou t of transfer_bu ffer_length) were 
1050 *      transferred.  It will normally be the same as requ ested, u nless 
1051 *      either an error was reported or a short read was performed. 
1052 *      The URB _SHORT_NOT_OK transfer flag may be u sed to make su ch 
1053 *      short reads be reported as errors. 
1054 * @setu p_packet: Only u sed for control transfers, this points to eight bytes 
1055 *      of setu p data.  Control transfers always start by sending this data 
1056 *      to the device.  Then transfer_bu ffer is read or written, if needed. 
1057 * @setu p_dma: DMA pointer for the setu p packet.  The caller mu st not u se 
1058 *      this field; setu p_packet mu st point to a valid bu ffer. 
1059 * @start_frame: Retu rns the initial frame for isochronou s transfers. 
1060 * @nu mber_of_packets: Lists the nu mber of ISO transfer bu ffers. 
1061 * @interval: Specifies the polling interval for interru pt or isochronou s 
1062 *      transfers.  The u nits are frames (milliseconds) for fu ll and low 
1063 *      speed devices, and microframes (1/8 millisecond) for highspeed 
1064 *      and Su perSpeed devices. 
1065 * @error_cou nt: Retu rns the nu mber of ISO transfers that reported errors. 
1066 * @context: For u se in completion fu nctions.  This normally points to 
1067 *      requ est-specific driver context. 
1068 * @complete: Completion handler. This URB is passed as the parameter to the 
1069 *      completion fu nction.  The completion fu nction may then do what 
1070 *      it likes with the URB , inclu ding resu bmitting or freeing it. 
1071 * @iso_frame_desc: U sed to provide arrays of ISO transfer bu ffers and to 
1072 *      collect the transfer statu s for each bu ffer. 
1073 * 
1074 * This stru ctu re identifies U SB transfer requ ests.  URB s mu st be allocated by 
1075 * calling u sb_alloc_urb () and freed with a call to u sb_free_urb (). 
1076 * Initialization may be done u sing variou s u sb_fill_*_urb () fu nctions.  URB s 
1077 * are su bmitted u sing u sb_su bmit_urb (), and pending requ ests may be canceled 
1078 * u sing u sb_u nlink_urb () or u sb_kill_urb (). 
1079 * 
1080 * Data Transfer Bu ffers: 
1081 * 
1082 * Normally drivers provide I/O bu ffers allocated with kmalloc() or otherwise 
1083 * taken from the general page pool.  That is provided by transfer_bu ffer 
1084 * (control requ ests also u se setu p_packet), and host controller drivers 
1085 * perform a dma mapping (and u nmapping) for each bu ffer transferred.  Those 
1086 * mapping operations can be expensive on some platforms (perhaps u sing a dma 
1087 * bou nce bu ffer or talking to an IOMMU ), 
1088 * althou gh they're cheap on commodity x86 and ppc hardware. 
1089 * 
1090 * Alternatively, drivers may pass the URB _NO_TRANSFER_DMA_MAP transfer flag, 
1091 * which tells the host controller driver that no su ch mapping is needed for 
1092 * the transfer_bu ffer since 
1093 * the device driver is DMA-aware.  For example, a device driver might 
1094 * allocate a DMA bu ffer with u sb_alloc_coherent() or call u sb_bu ffer_map(). 
1095 * When this transfer flag is provided, host controller drivers will 
1096 * attempt to u se the dma address fou nd in the transfer_dma 
1097 * field rather than determining a dma address themselves. 
1098 * 
1099 * Note that transfer_bu ffer mu st still be set if the controller 
1100 * does not su pport DMA (as indicated by bu s.u ses_dma) and when talking 
1101 * to root hu b. If you have to trasfer between highmem zone and the device 
1102 * on su ch controller, create a bou nce bu ffer or bail ou t with an error. 
1103 * If transfer_bu ffer cannot be set (is in highmem) and the controller is DMA 
1104 * capable, assign NU LL to it, so that u sbmon knows not to u se the valu e. 
1105 * The setu p_packet mu st always be set, so it cannot be located in highmem. 
1106 * 
1107 * Initialization: 
1108 * 
1109 * All URB s su bmitted mu st initialize the dev, pipe, transfer_flags (may be 
1110 * zero), and complete fields.  All URB s mu st also initialize 
1111 * transfer_bu ffer and transfer_bu ffer_length.  They may provide the 
1112 * URB _SHORT_NOT_OK transfer flag, indicating that short reads are 
1113 * to be treated as errors; that flag is invalid for write requ ests. 
1114 * 
1115 * Bu lk URB s may 
1116 * u se the URB _ZERO_PACKET transfer flag, indicating that bu lk OU T transfers 
1117 * shou ld always terminate with a short packet, even if it means adding an 
1118 * extra zero length packet. 
1119 * 
1120 * Control URB s mu st provide a valid pointer in the setu p_packet field. 
1121 * U nlike the transfer_bu ffer, the setu p_packet may not be mapped for DMA 
1122 * beforehand. 
1123 * 
1124 * Interru pt URB s mu st provide an interval, saying how often (in milliseconds 
1125 * or, for highspeed devices, 125 microsecond u nits) 
1126 * to poll for transfers.  After the URB has been su bmitted, the interval 
1127 * field reflects how the transfer was actu ally schedu led. 
1128 * The polling interval may be more frequ ent than requ ested. 
1129 * For example, some controllers have a maximu m interval of 32 milliseconds, 
1130 * while others su pport intervals of u p to 1024 milliseconds. 
1131 * Isochronou s URB s also have transfer intervals.  (Note that for isochronou s 
1132 * endpoints, as well as high speed interru pt endpoints, the encoding of 
1133 * the transfer interval in the endpoint descriptor is logarithmic. 
1134 * Device drivers mu st convert that valu e to linear u nits themselves.) 
1135 * 
1136 * Isochronou s URB s normally u se the URB _ISO_ASAP transfer flag, telling 
1137 * the host controller to schedu le the transfer as soon as bandwidth 
1138 * u tilization allows, and then set start_frame to reflect the actu al frame 
1139 * selected du ring su bmission.  Otherwise drivers mu st specify the start_frame 
1140 * and handle the case where the transfer can't begin then.  However, drivers 
1141 * won't know how bandwidth is cu rrently allocated, and while they can 
1142 * find the cu rrent frame u sing u sb_get_cu rrent_frame_nu mber () they can't 
1143 * know the range for that frame nu mber.  (Ranges for frame cou nter valu es 
1144 * are HC-specific, and can go from 256 to 65536 frames from "now".) 
1145 * 
1146 * Isochronou s URB s have a different data transfer model, in part becau se 
1147 * the qu ality of service is only "best effort".  Callers provide specially 
1148 * allocated URB s, with nu mber_of_packets worth of iso_frame_desc stru ctu res 
1149 * at the end.  Each su ch packet is an individu al ISO transfer.  Isochronou s 
1150 * URB s are normally qu eu ed, su bmitted by drivers to arrange that 
1151 * transfers are at least dou ble bu ffered, and then explicitly resu bmitted 
1152 * in completion handlers, so 
1153 * that data (su ch as au dio or video) streams at as constant a rate as the 
1154 * host controller schedu ler can su pport. 
1155 * 
1156 * Completion Callbacks: 
1157 * 
1158 * The completion callback is made in_interru pt(), and one of the first 
1159 * things that a completion handler shou ld do is check the statu s field. 
1160 * The statu s field is provided for all URB s.  It is u sed to report 
1161 * u nlinked URB s, and statu s for all non-ISO transfers.  It shou ld not 
1162 * be examined before the URB is retu rned to the completion handler. 
1163 * 
1164 * The context field is normally u sed to link URB s back to the relevant 
1165 * driver or requ est state. 
1166 * 
1167 * When the completion callback is invoked for non-isochronou s URB s, the 
1168 * actu al_length field tells how many bytes were transferred.  This field 
1169 * is u pdated even when the URB terminated with an error or was u nlinked. 
1170 * 
1171 * ISO transfer statu s is reported in the statu s and actu al_length fields 
1172 * of the iso_frame_desc array, and the nu mber of errors is reported in 
1173 * error_cou nt.  Completion callbacks for ISO transfers will normally 
1174 * (re)su bmit URB s to ensu re a constant transfer rate. 
1175 * 
1176 * Note that even fields marked "pu blic" shou ld not be tou ched by the driver 
1177 * when the urb is owned by the hcd, that is, since the call to 
1178 * u sb_su bmit_urb () till the entry into the completion rou tine. 
1179 */ 
1180 stru ct urb {
1181          /* private: u sb core and host controller only fields in the urb */ 
1182          stru ct kref kref ;               /* reference cou nt of the URB */ 
1183          void *hcpriv;                   /* private data for host controller */ 
1184          atomic_t u se_cou nt ;             /* concu rrent su bmissions cou nter */ 
1185          atomic_t reject;                /* su bmissions will fail */ 
1186          int u nlinked;                   /* u nlink error code */ 
1187 
1188          /* pu blic: docu mented fields in the urb that can be u sed by drivers */ 
1189          stru ct list_head urb _list ;      /* list head for u se by the urb 's 
1190                                          * cu rrent owner */ 
1191          stru ct list_head anchor_list;   /* the URB may be anchored */ 
1192          stru ct u sb_anchor *anchor;
1193          stru ct u sb_device *dev ;         /* (in) pointer to associated device */ 
1194          stru ct u sb_host_endpoint *ep ;   /* (internal) pointer to endpoint */ 
1195          u nsigned int pipe ;              /* (in) pipe information */ 
1196          u nsigned int stream_id ;         /* (in) stream ID */ 
1197          int statu s ;                     /* (retu rn) non-ISO statu s */ 
1198          u nsigned int transfer_flags;    /* (in) URB _SHORT_NOT_OK | ...*/ 
1199          void *transfer_bu ffer;          /* (in) associated data bu ffer */ 
1200          dma_addr_t transfer_dma;        /* (in) dma addr for transfer_bu ffer */ 
1201          stru ct scatterlist *sg;         /* (in) scatter gather bu ffer list */ 
1202          int nu m_sgs;                    /* (in) nu mber of entries in the sg list */ 
1203          u 32 transfer_bu ffer_length;     /* (in) data bu ffer length */ 
1204          u 32 actu al_length;              /* (retu rn) actu al transfer length */ 
1205          u nsigned char *setu p_packet ;    /* (in) setu p packet (control only) */ 
1206          dma_addr_t setu p_dma ;           /* (in) dma addr for setu p_packet */ 
1207          int start_frame;                /* (modify) start frame (ISO) */ 
1208          int nu mber_of_packets;          /* (in) nu mber of ISO packets */ 
1209          int interval ;                   /* (modify) transfer interval 
1210                                          * (INT/ISO) */ 
1211          int error_cou nt ;                /* (retu rn) nu mber of ISO errors */ 
1212          void *context ;                  /* (in) context for completion */ 
1213          u sb_complete_t complete ;        /* (in) completion rou tine */ 
1214          stru ct u sb_iso_packet_descriptor iso_frame_desc[0];
1215                                          /* (in) ISO ONLY */ 
1216 };
1217 
1218 /* ----------------------------------------------------------------------- */

 

 

6. Linux usb 驱动的相关操作函数

 

 int usb_register(struct usb_driver *d);
void usb_deregister(struct usb_driver *d);
Functions used to register and unregister a USB driver from the USB core.

 

 这两个函数主要用来注册usb driver与解注册usb driver.

 

struct usb_device *interface_to_usbdev(struct usb_interface *intf);
Retrieves the controlling struct usb_device * out of a struct usb_interface *.

 

 

返回一个usb接口返回一个usb_device.

 

void usb_set_intfdata(struct usb_interface *intf, void *data);
void *usb_get_intfdata(struct usb_interface *intf);
Functions to set and get access to the private data pointer section within the
struct usb_interface.

 

 

设置private data和是返回private data.

 

int usb_register_dev(struct usb_interface *intf, struct usb_class_driver
*class_driver);
void usb_deregister_dev(struct usb_interface *intf, struct usb_class_driver
*class_driver);
Functions used to register and unregister a specific struct usb_interface * structure
with a struct usb_class_driver * structure.

 

注册usb接口驱动和解注册usb接口驱动，接口驱动也就是设备驱动。

 

 

 

struct urb *usb_alloc_urb(int iso_packets, int mem_flags);
void usb_free_urb(struct urb *urb);
Functions used to create and destroy a struct usb urb *.

 

分配和释放urb.

 

void usb_fill_int_urb(struct urb *urb, struct usb_device *dev, unsigned int
pipe, void *transfer_buffer, int buffer_length, usb_complete_t complete,
void *context, int interval);
void usb_fill_bulk_urb(struct urb *urb, struct usb_device *dev, unsigned int
pipe, void *transfer_buffer, int buffer_length, usb_complete_t complete,
void *context);
void usb_fill_control_urb(struct urb *urb, struct usb_device *dev, unsigned
int pipe, unsigned char *setup_packet, void *transfer_buffer, int
buffer_ length, usb_complete_t complete, void *context);
Functions used to initialize a struct urb before it is submitted to the USB core.

 

 

这三个函数是用来初始化urb.

 

参数:

struct urb* urb 要初始化的urb结构体。

struct usb_device *dev urb发送到的设备

unsigned int pipe  usb_sndintpipe和usb_rcvintpipe分别是usb发送端点管道和接收端点管道

void *transfer_buffer 接收或发送数据的缓冲区

int buffer_length 缓冲区的长度

usb_complete_t  urb完成时的回调函数

 

int usb_bulk_msg(struct usb_device *usb_dev, unsigned int pipe, void *data,
int len, int *actual_length, int timeout);
int usb_control_msg(struct usb_device *dev, unsigned int pipe, __u8 request,
__u8 requesttype, __u16 value, __u16 index, void *data, __u16 size,
int timeout);
Functions used to send or receive USB data without having to use a struct urb.

 

这两个函数的usb接收或发送数据没有使用urb结构体。

 

 

7. skelton程序

 

/*
 * USB Skeleton driver - 2.2
 *
 * Copyright (C) 2001-2004 Greg Kroah-Hartman ([e-mail])
 *
 *    This program is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU General Public License as
 *    published by the Free Software Foundation, version 2.
 *
 * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
 * but has been rewritten to be easier to read and use.
 *
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/kref.h>
#include <asm/uaccess.h>
#include <linux/usb.h>
#include <linux/mutex.h>


/* Define these values to match your devices */
#define USB_SKEL_VENDOR_ID    0xfff0
#define USB_SKEL_PRODUCT_ID    0xfff0

/* table of devices that work with this driver */
static struct usb_device_id skel_table [] = {
    { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
    { }                    /* Terminating entry */
};
MODULE_DEVICE_TABLE(usb, skel_table);


/* Get a minor range for your devices from the usb maintainer */
#define USB_SKEL_MINOR_BASE    192 //次设备号

/* our private defines. if this grows any larger, use your own .h file */
#define MAX_TRANSFER        (PAGE_SIZE - 512)
#define WRITES_IN_FLIGHT    8

/* Structure to hold all of our device specific stuff */
struct usb_skel {
      size_t udev;
    struct usb_device       *dev;            /* the usb device for this device */
    struct usb_interface    *interface;        /* the interface for this device */
    struct semaphore    limit_sem;        /* limiting the number of writes in progress */
    unsigned char           *bulk_in_buffer;    /* the buffer to receive data */
    size_t            bulk_in_size;        /* the size of the receive buffer */
    __u8            bulk_in_endpointAddr;    /* the address of the bulk in endpoint */
    __u8            bulk_out_endpointAddr;    /* the address of the bulk out endpoint */
    struct kref        kref;
    struct mutex        io_mutex;        /* synchronize I/O with disconnect */
};
#define to_skel_dev(d) container_of(d, struct usb_skel, kref)

static struct usb_driver skel_driver;

static void skel_delete(struct kref *kref)
{
    struct usb_skel *dev = to_skel_dev(kref);

    usb_put_dev(dev->udev);
    kfree(dev->bulk_in_buffer);
    kfree(dev);
}

static int skel_open(struct inode *inode, struct file *file)
{
    struct usb_skel *dev;
    struct usb_interface *interface;
    int subminor;
    int retval = 0;

    subminor = iminor(inode); 

    interface = usb_find_interface(&skel_driver, subminor);
    if (!interface) {
        err ("%s - error, can't find device for minor %d",
             __FUNCTION__, subminor);
        retval = -ENODEV;
        goto exit;
    }

    dev = usb_get_intfdata(interface);
    if (!dev) {
        retval = -ENODEV;
        goto exit;
    }

    /* prevent the device from being autosuspended */
    retval = usb_autopm_get_interface(interface);
    if (retval)
        goto exit;

    /* increment our usage count for the device */
    kref_get(&dev->kref);

    /* save our object in the file's private structure */
    file->private_data = dev;

exit:
    return retval;
}

static int skel_release(struct inode *inode, struct file *file)
{
    struct usb_skel *dev;

    dev = (struct usb_skel *)file->private_data;
    if (dev == NULL)
        return -ENODEV;

    /* allow the device to be autosuspended */
    mutex_lock(&dev->io_mutex);
    if (dev->interface)
        usb_autopm_put_interface(dev->interface);
    mutex_unlock(&dev->io_mutex);

    /* decrement the count on our device */
    kref_put(&dev->kref, skel_delete);
    return 0;
}

static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
{
    struct usb_skel *dev;
    int retval;
    int bytes_read;

    dev = (struct usb_skel *)file->private_data;

    mutex_lock(&dev->io_mutex);
    if (!dev->interface) {        /* disconnect() was called */
        retval = -ENODEV;
        goto exit;
    }

    /* do a blocking bulk read to get data from the device */   //usb_bulk_msg没有使用urb 
    retval = usb_bulk_msg(dev->udev,
                  usb_rcvbulkpipe(dev->udev, dev->bulk_in_endpointAddr),
                  dev->bulk_in_buffer,
                  min(dev->bulk_in_size, count),
                  &bytes_read, 10000);

    /* if the read was successful, copy the data to userspace */
    if (!retval) {
        if (copy_to_user(buffer, dev->bulk_in_buffer, bytes_read)) //复制到用户空间
            retval = -EFAULT;
        else
            retval = bytes_read;
    }

exit:
    mutex_unlock(&dev->io_mutex);
    return retval;
}

static void skel_write_bulk_callback(struct urb *urb)
{
    struct usb_skel *dev;

    dev = (struct usb_skel *)urb->context;

    /* sync/async unlink faults aren't errors */
    if (urb->status &&
        !(urb->status == -ENOENT ||
          urb->status == -ECONNRESET ||
          urb->status == -ESHUTDOWN)) {
        err("%s - nonzero write bulk status received: %d",
            __FUNCTION__, urb->status);
    }

    /* free up our allocated buffer */
    usb_buffer_free(urb->dev, urb->transfer_buffer_length,
            urb->transfer_buffer, urb->transfer_dma);
    up(&dev->limit_sem);
}

//首先创建一个urb和buffer,初始化urb,然后提交urb.
static ssize_t skel_write(struct file *file, const char *user_buffer, size_t count, loff_t *ppos)
{

    struct usb_skel *dev;
    int retval = 0;
    struct urb *urb = NULL;
    char *buf = NULL;
    size_t writesize = min(count, (size_t)MAX_TRANSFER);

    dev = (struct usb_skel *)file->private_data;

    /* verify that we actually have some data to write */
    if (count == 0)
        goto exit;

    /* limit the number of URBs in flight to stop a user from using up all RAM */
    if (down_interruptible(&dev->limit_sem)) {
        retval = -ERESTARTSYS;
        goto exit;
    }

    mutex_lock(&dev->io_mutex);
    if (!dev->interface) {        /* disconnect() was called */
        retval = -ENODEV;
        goto error;
    }

    /* create a urb, and a buffer for it, and copy the data to the urb */
    urb = usb_alloc_urb(0, GFP_KERNEL);
    if (!urb) {
        retval = -ENOMEM;
        goto error;
    }

    buf = usb_buffer_alloc(dev->udev, writesize, GFP_KERNEL, &urb->transfer_dma);
    if (!buf) {
        retval = -ENOMEM;
        goto error;
    }

    if (copy_from_user(buf, user_buffer, writesize)) {
        retval = -EFAULT;
        goto error;
    }

    /* initialize the urb properly */
    usb_fill_bulk_urb(urb, dev->udev,
              usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
              buf, writesize, skel_write_bulk_callback, dev);
    urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

    /* send the data out the bulk port */
    retval = usb_submit_urb(urb, GFP_KERNEL);
    if (retval) {
        err("%s - failed submitting write urb, error %d", __FUNCTION__, retval);
        goto error;
    }

    /* release our reference to this urb, the USB core will eventually free it entirely */
    usb_free_urb(urb);

    mutex_unlock(&dev->io_mutex);
    return writesize;

error:
    if (urb) {
        usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
        usb_free_urb(urb);
    }
    mutex_unlock(&dev->io_mutex);
    up(&dev->limit_sem);

exit:
    return retval;
}

static const struct file_operations skel_fops = {
    .owner =    THIS_MODULE,
    .read =        skel_read,
    .write =    skel_write,
    .open =        skel_open,
    .release =    skel_release,
};

/*
 * usb class driver info in order to get a minor number from the usb core,
 * and to have the device registered with the driver core
 */
static struct usb_class_driver skel_class = {
    .name =        "skel%d",
    .fops =        &skel_fops,
    .minor_base =    USB_SKEL_MINOR_BASE,
};

static int skel_probe(struct usb_interface *interface, const struct usb_device_id *id)
{
    struct usb_skel *dev;
    struct usb_host_interface *iface_desc; //usb_host_interface包含usb interface的所有设置
    struct usb_endpoint_descriptor *endpoint; //这个结构体是usb端点描述符
    size_t buffer_size;
    int i;
    int retval = -ENOMEM;

    /* allocate memory for our device state and initialize it */
    dev = kzalloc(sizeof(*dev), GFP_KERNEL);
    if (!dev) {
        err("Out of memory");
        goto error;
    }
    kref_init(&dev->kref);
    sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
    mutex_init(&dev->io_mutex);

    dev->udev = usb_get_dev(interface_to_usbdev(interface)); //增加使用计数
    dev->interface = interface;

    /* set up the endpoint information */
    /* use only the first bulk-in and bulk-out endpoints */
    iface_desc = interface->cur_altsetting;
    for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
        endpoint = &iface_desc->endpoint[i].desc;

        if (!dev->bulk_in_endpointAddr &&
            usb_endpoint_is_bulk_in(endpoint)) {
            /* we found a bulk in endpoint */
            buffer_size = le16_to_cpu(endpoint->wMaxPacketSize);
            dev->bulk_in_size = buffer_size;
            dev->bulk_in_endpointAddr = endpoint->bEndpointAddress;
            dev->bulk_in_buffer = kmalloc(buffer_size, GFP_KERNEL);
            if (!dev->bulk_in_buffer) {
                err("Could not allocate bulk_in_buffer");
                goto error;
            }
        }

        if (!dev->bulk_out_endpointAddr &&
            usb_endpoint_is_bulk_out(endpoint)) {
            /* we found a bulk out endpoint */
            dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
        }
    }
    if (!(dev->bulk_in_endpointAddr && dev->bulk_out_endpointAddr)) {
        err("Could not find both bulk-in and bulk-out endpoints");
        goto error;
    }

    /* save our data pointer in this interface device */
    usb_set_intfdata(interface, dev);

    /* we can register the device now, as it is ready */
    retval = usb_register_dev(interface, &skel_class);  //注册usb设备
    if (retval) {
        /* something prevented us from registering this driver */
        err("Not able to get a minor for this device.");
        usb_set_intfdata(interface, NULL);
        goto error;
    }

    /* let the user know what node this device is now attached to */
    info("USB Skeleton device now attached to USBSkel-%d", interface->minor);
    return 0;

error:
    if (dev)
        kref_put(&dev->kref, skel_delete);
    return retval;
}

static void skel_disconnect(struct usb_interface *interface)
{
    struct usb_skel *dev;
    int minor = interface->minor;

    /* prevent skel_open() from racing skel_disconnect() */
    lock_kernel();

    dev = usb_get_intfdata(interface);
    usb_set_intfdata(interface, NULL);

    /* give back our minor */
    usb_deregister_dev(interface, &skel_class);

    /* prevent more I/O from starting */
    mutex_lock(&dev->io_mutex);
    dev->interface = NULL;
    mutex_unlock(&dev->io_mutex);

    unlock_kernel();

    /* decrement our usage count */
    kref_put(&dev->kref, skel_delete);

    info("USB Skeleton #%d now disconnected", minor);
}

static struct usb_driver skel_driver = {
    .name =        "skeleton",
    .probe =    skel_probe,
    .disconnect =    skel_disconnect,
    .id_table =    skel_table,
};

static int __init usb_skel_init(void)
{
    int result;
   
    /* register this driver with the USB subsystem */
    result = usb_register(&skel_driver);
    if (result)
        err("usb_register failed. Error number %d", result);

    return result;
}

static void __exit usb_skel_exit(void)
{ //向usb子系统注册这个驱动
    /* deregister this driver with the USB subsystem */
    usb_deregister(&skel_driver);
}

module_init(usb_skel_init);
module_exit(usb_skel_exit);

MODULE_LICENSE("GPL");

 

 

分析:

skeleton.c 在/driver/usb/ 目录下，它是一个骨架驱动程序。

skeleton首先向usb子系统中注册驱动，然后注册设备。通常所说的usb驱动是指usb接口驱动。即完成一定的功能，数据处理。面 usb driver通过扫描确定usb设备是否在本驱动的设备列表中，即一个usb driver可能对应多个usb设备，它是用来辨别usb设备的。当usb设备移除时，调用disconnect函数。usb driver用于识别usb interface driver.

最后记住，一个接口对应一个设备驱动，主机与设备之间的数据传输是通过端点来实现的。urb是设备与主机之间数据交换的中介。

关于usb 主机驱动就介绍到这里了。