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Linux USB驱动详解_setu84
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原文地址：http://blog.csdn.net/chenjin_zhong/article/details/6329316
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 ctusb_driver - identifiesU SB interface driver tou sbcore
789* @name: The driver name shou ld beu niqu e amongU 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 andu ses
793* u sb_set_intfdata() to associate driver-specific data with the
794* interface. It may alsou se u sb_set_interface() to specify the
795* appropriate altsetting. Ifu 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 beingu nloaded.
801* @u nlocked_ioctl:U sed for drivers that want to talk tou serspace throu gh
802* the "u sbfs" filesystem. This lets devices provide ways to
803* expose information tou ser space regardless of where they
804* do (or don't) showu 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 byu sb_reset_device() when the device
810* is abou t to be reset.
811* @post_reset: Called byu 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, theU 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, theU SB core will not allow au tosu spend
822* for interfaces bou nd to this driver.
823* @soft_u nbind: if set to 1, theU SB core will not killU 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 isu sed in hotplu gging. It holds a set of descriptors,
830* and specialized data may be associated with each entry. That table
831* isu 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* andu 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 (byu nlinking
839* them as necessary, and blockingu ntil the u nlinks complete).
840*/
841stru ctusb_driver{
842 const char *name;
843
844 int (*probe) (stru ct u sb_interface*intf,
845 const stru ctu sb_device_id*id);
846
847 void (*disconnect) (stru ct u sb_interface*intf);
848
849 int (*u nlocked_ioctl) (stru ctu sb_interface*intf,u nsigned int code,
850 void *bu f);
851
852 int (*su spend) (stru ct u sb_interface *intf,pm_message_tmessage);
853 int (*resu me) (stru ct u sb_interface *intf);
854 int (*reset_resu me)(stru ctu sb_interface*intf);
855
856 int (*pre_reset)(stru ct u sb_interface*intf);
857 int (*post_reset)(stru ctu sb_interface*intf);
858
859 const stru ctu sb_device_id*id_table;
860
861 stru ctu sb_dynidsdynids;
862 stru ctu sbdrv_wrapdrvwrap;
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*/
312stru ctu sb_bu s {
313 stru ctdevice *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 controlleru se DMA? */
317 u 8 u ses_pio_for_control; /*
318 * Does the host controlleru 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 ctu sb_devmap devmap; /* device address allocation map */
330 stru ctusb_device * root_hu b; /* Root hu b */
331 stru ctu sb_bu s *hs_companion; /* Companion EHCI bu s, if any */
332 stru ctlist_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 isu 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 ctdentry *u sbfs_dentry; /*u sbfs dentry entry for the bu s */
346#endif
347
348#ifdefined (CONFIG_U SB_MON) ||defined(CONFIG_U SB_MON_MODU LE)
349 stru ctmon_bu s *mon_bu s ; /* non-nu ll when associated */
350 int monitored; /* non-zero when monitored */
351#endif
352};
353
**
370* stru ctusb_device - kernel's representation of aU SB device
371* @devnu m: device nu mber; address on aU SB bu s
372* @devpath: device ID string foru se in messages (e.g., /port/...)
373* @rou te: tree topology hex string foru 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 ofU 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 canu se it;
396* (u ser space) policy determines if we au thorize this device to be
397* u sed or not. By defau lt, wiredU SB devices are au thorized.
398* WU SB devices are not,u ntil we au thorize them fromu ser space.
399* FIXME -- complete doc
400* @au thenticated: Crypto au thentication passed
401* @wu sb: device is WirelessU 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 foru sbfs device
408* access fromu 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 ofU 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 WirelessU 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. Insteadu se
424*u sb_set_device_state().
425*/
426stru ctusb_device{
427 int devnu m;
428 char devpath[16];
429 u 32 rou te;
430 enu musb_device _state state;
431 enu musb_device _speed speed;
432
433 stru ctu sb_tt *tt;
434 int ttport;
435
436 u nsigned int toggle [2];
437
438 stru ctusb_device*parent;
439 stru ctu sb_bu s*bu s;
440 stru ctu sb_host_endpointep0;
441
442 stru ctdevicedev;
443
444 stru ctusb_device _descriptordescriptor;
445 stru ctu sb_host_config*config;
446
447 stru ctu sb_host_config*actconfig;
448 stru ctu sb_host_endpoint*ep_in[16];
449 stru ctu sb_host_endpoint*ep_ou t[16];
450
451 char **rawdescriptors;
452
453 u nsigned short bu s_mA;
454 u 8portnu m;
455 u 8level;
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 ctlist_headfilelist;
471#ifdef CONFIG_USB_DEVICE _CLASS
472 stru ctdevice*u sb_classdev;
473#endif
474#ifdef CONFIG_USB_DEVICE FS
475 stru ctdentry*u sbfs_dentry;
476#endif
477
478 int maxchild;
479 stru ctusb_device*children[U SB_MAXCHILDREN];
480
481 u 32qu irks;
482 atomic_tu rbnu m;
483
484 u nsigned long active_du ration;
485
486#ifdefCONFIG_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 ctwu sb_dev*wu sb_dev;
493 int slot_id;
494};
495#defineto_usb_device(d)container_of(d, stru ctusb_device, dev)
496
497static inline stru ctusb_device*interface_to_u sbdev(stru ctu sb_interface*intf)
498{
499 retu rnto_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 structusb_host_interface*altsetting;
163
164 structusb_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 structusb_interface_assoc_descriptor *intf_assoc;
171
172 intminor; /* minor number this interface is
173 * bound to */
174 enumusb_interface_conditioncondition; /* 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 structdevicedev; /* interface specific device info */
185 structdevice*usb_dev;
186 atomic_tpm_usage_cnt; /* usage counter for autosuspend */
187 structwork_structreset_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 */
77stru ctusb_host_interface {
78 stru ctu sb_interface_descriptordesc ;
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 ctu 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 ctusb_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 byu sbcore
54* @hcpriv: foru se by HCD; typically holds hardware dma qu eu e head (QH)
55* with one or more transfer descriptors (TDs) peru 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 givenU SB configu ration.
63*/
64stru ctusb_host_endpoint {
65 stru ctu sb_endpoint_descriptor desc ;
66 stru ctu sb_ss_ep_comp_descriptor ss_ep_comp;
67 stru ctlist_head u rb_list ;
68 void *hcpriv;
69 stru ctep_device *ep_dev; /* For sysfs info */
70
71 u nsigned char *extra; /* Extra descriptors */
72 int extralen;
73 intenabled ;
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 cturb -U SB Requ est Block
1007* @urb _list: Foru se by cu rrent owner of the URB .
1008* @anchor_list: membership in the list of an anchor
1009* @anchor: to anchorURB 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 exampleu sb_sndbu lkpipe() oru 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 theU 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 onlyu se it
1025* to tell whether theURB 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 beu sed to affect howURB
1028* su bmission,u nlinking, or operation are handled. Different
1029* kinds ofURB canu se different flags.
1030* @transfer_bu ffer: This identifies the bu ffer to (or from) which the I/O
1031* requ est will be performedu nlessURB _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 isu sed for the data
1036* stage of control transfers.
1037* @transfer_dma: When transfer_flags inclu desURB _NO_TRANSFER_DMA_MAP,
1038* the device driver is saying that it provided this DMA address,
1039* which the host controller driver shou ldu 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 brokenu 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 isu 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* TheURB _SHORT_NOT_OK transfer flag may beu sed to make su ch
1053* short reads be reported as errors.
1054* @setu p_packet: Onlyu 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 notu 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. Theu 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: Foru se in completion fu nctions. This normally points to
1067* requ est-specific driver context.
1068* @complete: Completion handler. ThisURB is passed as the parameter to the
1069* completion fu nction. The completion fu nction may then do what
1070* it likes with theURB , 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 identifiesU SB transfer requ ests. URB s mu st be allocated by
1075* callingu sb_alloc_urb () and freed with a call tou sb_free_urb ().
1076* Initialization may be doneu sing variou su sb_fill_*_urb () fu nctions. URB s
1077* are su bmittedu sing u sb_su bmit_urb (), and pending requ ests may be canceled
1078*u sing u sb_u nlink_urb () oru 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 alsou se setu p_packet), and host controller drivers
1085* perform a dma mapping (andu nmapping) for each bu ffer transferred. Those
1086* mapping operations can be expensive on some platforms (perhapsu 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 theURB _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 withu sb_alloc_coherent() or callu sb_bu ffer_map().
1095* When this transfer flag is provided, host controller drivers will
1096* attempt tou 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 thatu sbmon knows not tou 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* AllURB s su bmitted mu st initialize the dev, pipe, transfer_flags (may be
1110* zero), and complete fields. AllURB 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 lkURB 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* ControlURB 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 ptURB s mu st provide an interval, saying how often (in milliseconds
1125* or, for highspeed devices, 125 microsecondu nits)
1126* to poll for transfers. After theURB 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 ofu p to 1024 milliseconds.
1131* Isochronou sURB 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 linearu nits themselves.)
1135*
1136* Isochronou sURB s normally u se theURB _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 frameu 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 sURB 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* allocatedURB 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 allURB 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 theURB is retu rned to the completion handler.
1163*
1164* The context field is normallyu 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 sURB s, the
1168* actu al_length field tells how many bytes were transferred. This field
1169* isu pdated even when the URB terminated with an error or wasu 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 bmitURB 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 theurb 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*/
1180stru cturb{
1181 /* private: u sb core and host controller only fields in theurb */
1182 stru ctkrefkref; /* reference cou nt of the URB */
1183 void *hcpriv; /* private data for host controller */
1184 atomic_tu se_cou nt; /* concu rrent su bmissions cou nter */
1185 atomic_treject; /* su bmissions will fail */
1186 intu nlinked; /* u nlink error code */
1187
1188 /* pu blic: docu mented fields in theurb that can beu sed by drivers */
1189 stru ctlist_headurb _list; /* list head for u se by the urb 's
1190 * cu rrent owner */
1191 stru ctlist_headanchor_list; /* theURB may be anchored */
1192 stru ctu sb_anchor*anchor;
1193 stru ctu sb_device*dev; /* (in) pointer to associated device */
1194 stru ctu 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 intstatu 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_ttransfer_dma; /* (in) dma addr for transfer_bu ffer */
1201 stru ctscatterlist*sg; /* (in) scatter gather bu ffer list */
1202 int nu m_sgs; /* (in) nu mber of entries in the sg list */
1203 u 32transfer_bu ffer_length; /* (in) data bu ffer length */
1204 u 32actu al_length; /* (retu rn) actu al transfer length */
1205 u nsigned char *setu p_packet; /* (in) setu p packet (control only) */
1206 dma_addr_tsetu 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 intinterval; /* (modify) transfer interval
1210 * (INT/ISO) */
1211 interror_cou nt; /* (retu rn) nu mber of ISO errors */
1212 void *context; /* (in) context for completion */
1213 u sb_complete_tcomplete; /* (in) completion rou tine */
1214 stru ctu 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 (greg@kroah.com)
*
* 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。
