简介
这篇主要是讲下usb_driver结构体中的id_table成员，也就是usb_device_id结构体，以及结合具体的cdc-ncm驱动的一些分析。
usb_device_id
在Linux内核中，使用usb_driver结构体描述一个USB设备驱动，在编写新的USB设备驱动时，主要应该完成的工作是probe（）和disconnect（）函数，即探测和断开函数，它们分别在设备被插入和拔出的时候调用，用于初始化和释放软硬件资源。
那这个probe函数跟要讲的usb_device_id是什么关系呢？
当USB核心检测到某个设备的属性和某个驱动程序的usb_device_id结构体所携带的信息一致时，这个驱动程序的probe（）函数就被执行。
以cdc-ncm驱动分析，代码路径drivers/net/usb/cdc_ncm.c，找到usb_driver，可以看到id_table成员变量为cdc_devs
而且probe函数的入参也有struct usb_device_id
回归正题，接着我们来看cdc-devs
结构体内容很多，我们这里陈列出来
static const struct usb_device_id cdc_devs[] = {
/* Ericsson MBM devices like F5521gw */
{ .match_flags = USB_DEVICE_ID_MATCH_INT_INFO
| USB_DEVICE_ID_MATCH_VENDOR,
.idVendor = 0x0bdb,
.bInterfaceClass = USB_CLASS_COMM,
.bInterfaceSubClass = USB_CDC_SUBCLASS_NCM,
.bInterfaceProtocol = USB_CDC_PROTO_NONE,
.driver_info = (unsigned long) &wwan_info,
},
/* Dell branded MBM devices like DW5550 */
{ .match_flags = USB_DEVICE_ID_MATCH_INT_INFO
| USB_DEVICE_ID_MATCH_VENDOR,
.idVendor = 0x413c,
.bInterfaceClass = USB_CLASS_COMM,
.bInterfaceSubClass = USB_CDC_SUBCLASS_NCM,
.bInterfaceProtocol = USB_CDC_PROTO_NONE,
.driver_info = (unsigned long) &wwan_info,
},
/* Toshiba branded MBM devices */
{ .match_flags = USB_DEVICE_ID_MATCH_INT_INFO
| USB_DEVICE_ID_MATCH_VENDOR,
.idVendor = 0x0930,
.bInterfaceClass = USB_CLASS_COMM,
.bInterfaceSubClass = USB_CDC_SUBCLASS_NCM,
.bInterfaceProtocol = USB_CDC_PROTO_NONE,
.driver_info = (unsigned long) &wwan_info,
},
/* tag Huawei devices as wwan */
{ USB_VENDOR_AND_INTERFACE_INFO(0x12d1,
USB_CLASS_COMM,
USB_CDC_SUBCLASS_NCM,
USB_CDC_PROTO_NONE),
.driver_info = (unsigned long)&wwan_info,
},
/* Infineon(now Intel) HSPA Modem platform */
{ USB_DEVICE_AND_INTERFACE_INFO(0x1519, 0x0443,
USB_CLASS_COMM,
USB_CDC_SUBCLASS_NCM, USB_CDC_PROTO_NONE),
.driver_info = (unsigned long)&wwan_noarp_info,
},
/* Generic CDC-NCM devices */
{ USB_INTERFACE_INFO(USB_CLASS_COMM,
USB_CDC_SUBCLASS_NCM, USB_CDC_PROTO_NONE),
.driver_info = (unsigned long)&cdc_ncm_info,
},
{
},
};
MODULE_DEVICE_TABLE(usb, cdc_devs);
其实会发现，能匹配到cdc-ncm这个驱动的，有很多种情况，因为各种匹配情况不同，最终呢不同的可能只是driver_info，而目前driver_info有三种，其实也就是description跟flags不同而已
在include/linux/usb/usbnet.h中可以找到driver_info的定义，其中就有对各种flag的解释
/* interface from the device/framing level "minidriver" to core */
struct driver_info {
char *description;
int flags;
/* framing is CDC Ethernet, not writing ZLPs (hw issues), or optionally: */
#define FLAG_FRAMING_NC 0x0001 /* guard against device dropouts */
#define FLAG_FRAMING_GL 0x0002 /* genelink batches packets */
#define FLAG_FRAMING_Z 0x0004 /* zaurus adds a trailer */
#define FLAG_FRAMING_RN 0x0008 /* RNDIS batches, plus huge header */
#define FLAG_NO_SETINT 0x0010 /* device can't set_interface() */
#define FLAG_ETHER 0x0020 /* maybe use "eth%d" names */
#define FLAG_FRAMING_AX 0x0040 /* AX88772/178 packets */
#define FLAG_WLAN 0x0080 /* use "wlan%d" names */
#define FLAG_AVOID_UNLINK_URBS 0x0100 /* don't unlink urbs at usbnet_stop() */
#define FLAG_SEND_ZLP 0x0200 /* hw requires ZLPs are sent */
#define FLAG_WWAN 0x0400 /* use "wwan%d" names */
#define FLAG_LINK_INTR 0x0800 /* updates link (carrier) status */
#define FLAG_POINTTOPOINT 0x1000 /* possibly use "usb%d" names */
/*
* Indicates to usbnet, that USB driver accumulates multiple IP packets.
* Affects statistic (counters) and short packet handling.
*/
#define FLAG_MULTI_PACKET 0x2000
#define FLAG_RX_ASSEMBLE 0x4000 /* rx packets may span >1 frames */
#define FLAG_NOARP 0x8000 /* device can't do ARP */
/* init device ... can sleep, or cause probe() failure */
int (*bind)(struct usbnet *, struct usb_interface *);
/* cleanup device ... can sleep, but can't fail */
void (*unbind)(struct usbnet *, struct usb_interface *);
/* reset device ... can sleep */
int (*reset)(struct usbnet *);
/* stop device ... can sleep */
int (*stop)(struct usbnet *);
/* see if peer is connected ... can sleep */
int (*check_connect)(struct usbnet *);
/* (dis)activate runtime power management */
int (*manage_power)(struct usbnet *, int);
/* for status polling */
void (*status)(struct usbnet *, struct urb *);
/* link reset handling, called from defer_kevent */
int (*link_reset)(struct usbnet *);
/* fixup rx packet (strip framing) */
int (*rx_fixup)(struct usbnet *dev, struct sk_buff *skb);
/* fixup tx packet (add framing) */
struct sk_buff *(*tx_fixup)(struct usbnet *dev,
struct sk_buff *skb, gfp_t flags);
/* recover from timeout */
void (*recover)(struct usbnet *dev);
/* early initialization code, can sleep. This is for minidrivers
* having 'subminidrivers' that need to do extra initialization
* right after minidriver have initialized hardware. */
int (*early_init)(struct usbnet *dev);
/* called by minidriver when receiving indication */
void (*indication)(struct usbnet *dev, void *ind, int indlen);
/* rx mode change (device changes address list filtering) */
void (*set_rx_mode)(struct usbnet *dev);
/* for new devices, use the descriptor-reading code instead */
int in; /* rx endpoint */
int out; /* tx endpoint */
unsigned long data; /* Misc driver specific data */
};
内核中与usb_device_id相关的宏
前面提到我们是根据usb_device_id 结构体来进行probe，usb_device_id结构体如下
struct usb_device_id {
/* which fields to match against? */
__u16 match_flags;//与哪些字段匹配
/* Used for product specific matches; range is inclusive */
/* 用于特定产品匹配；范围包括如下 */
__u16 idVendor;
__u16 idProduct;
__u16 bcdDevice_lo;//最小的版本
__u16 bcdDevice_hi;//最大的版本
/* Used for device class matches */
/* 用于设备类匹配 */
__u8 bDeviceClass;//设备类型
__u8 bDeviceSubClass;//设备子类型
__u8 bDeviceProtocol;//协议
/* Used for interface class matches */
/* 用于接口类匹配 */
__u8 bInterfaceClass;
__u8 bInterfaceSubClass;
__u8 bInterfaceProtocol;
/* Used for vendor-specific interface matches */
/* 用于供应商特定的接口匹配 */
__u8 bInterfaceNumber;
/* not matched against */
kernel_ulong_t driver_info
__attribute__((aligned(sizeof(kernel_ulong_t))));
};
其中的match_flags主要是用来指定哪种方式来匹配，其可选择的类型如下
/* Some useful macros to use to create struct usb_device_id */
#define USB_DEVICE_ID_MATCH_VENDOR 0x0001
#define USB_DEVICE_ID_MATCH_PRODUCT 0x0002
#define USB_DEVICE_ID_MATCH_DEV_LO 0x0004
#define USB_DEVICE_ID_MATCH_DEV_HI 0x0008
#define USB_DEVICE_ID_MATCH_DEV_CLASS 0x0010
#define USB_DEVICE_ID_MATCH_DEV_SUBCLASS 0x0020
#define USB_DEVICE_ID_MATCH_DEV_PROTOCOL 0x0040
#define USB_DEVICE_ID_MATCH_INT_CLASS 0x0080
#define USB_DEVICE_ID_MATCH_INT_SUBCLASS 0x0100
#define USB_DEVICE_ID_MATCH_INT_PROTOCOL 0x0200
#define USB_DEVICE_ID_MATCH_INT_NUMBER 0x0400
那总的来说其实比如我们某个设备要匹配上这个驱动，也就是我们来填充这个结构体。内核中有一些跟usb_device_id相关的宏，这些宏都可以来生成一个usb_device_id结构体的实例。下面介绍几个常用的，所有的定义在include/linux/usb.h中都有。
-
根据制造商
ID和产品ID生成一个usb_device_id结构体的实例，在数组中增加该元素将意味着该驱动可支持与制造商ID、产品ID匹配的设备。其实也就是匹配特定的设备。USB_DEVICE(vendor, product) /** * USB_DEVICE - macro used to describe a specific usb device * @vend: the 16 bit USB Vendor ID * @prod: the 16 bit USB Product ID * * This macro is used to create a struct usb_device_id that matches a * specific device. */ #define USB_DEVICE(vend, prod) \ .match_flags = USB_DEVICE_ID_MATCH_DEVICE, \ .idVendor = (vend), \ .idProduct = (prod) -
根据制造商
ID、产品ID、产品版本的最小值和最大值生成一个usb_device_id结构体的实例，在数组中增加该元素将意味着该驱动可支持与制造商ID、产品ID匹配和lo~hi范围内版本的设备。USB_DEVICE_VER(vendor, product, lo, hi) /** * USB_DEVICE_VER - describe a specific usb device with a version range * @vend: the 16 bit USB Vendor ID * @prod: the 16 bit USB Product ID * @lo: the bcdDevice_lo value * @hi: the bcdDevice_hi value * * This macro is used to create a struct usb_device_id that matches a * specific device, with a version range. */ #define USB_DEVICE_VER(vend, prod, lo, hi) \ .match_flags = USB_DEVICE_ID_MATCH_DEVICE_AND_VERSION, \ .idVendor = (vend), \ .idProduct = (prod), \ .bcdDevice_lo = (lo), \ .bcdDevice_hi = (hi) -
用于创建一个匹配设备指定类型的
usb_device_id结构体实例。USB_DEVICE_INFO(class, subclass, protocol) /** * USB_DEVICE_INFO - macro used to describe a class of usb devices * @cl: bDeviceClass value * @sc: bDeviceSubClass value * @pr: bDeviceProtocol value * * This macro is used to create a struct usb_device_id that matches a * specific class of devices. */ #define USB_DEVICE_INFO(cl, sc, pr) \ .match_flags = USB_DEVICE_ID_MATCH_DEV_INFO, \ .bDeviceClass = (cl), \ .bDeviceSubClass = (sc), \ .bDeviceProtocol = (pr) -
用于创建一个匹配接口指定类型的
usb_device_id结构体实例USB_INTERFACE_INFO(class, subclass, protocol) /** * USB_INTERFACE_INFO - macro used to describe a class of usb interfaces * @cl: bInterfaceClass value * @sc: bInterfaceSubClass value * @pr: bInterfaceProtocol value * * This macro is used to create a struct usb_device_id that matches a * specific class of interfaces. */ #define USB_INTERFACE_INFO(cl, sc, pr) \ .match_flags = USB_DEVICE_ID_MATCH_INT_INFO, \ .bInterfaceClass = (cl), \ .bInterfaceSubClass = (sc), \ .bInterfaceProtocol = (pr)
那我们以最通用的/* Generic CDC-NCM devices */来讲，可以看到他是用了USB_INTERFACE_INFO这个宏，他的match_flags是USB_DEVICE_ID_MATCH_INT_INFO，也就是接口还有设备类型相关，然后还有相关的USB_CLASS_COMM USB_CDC_SUBCLASS_NCM ` USB_CDC_PROTO_NONE`这三个参数匹配的。
这三个参数宏定义为
#define USB_CLASS_COMM 2
#define USB_CDC_SUBCLASS_NCM 0x0d
#define USB_CDC_PROTO_NONE 0
现在设备上接入了一个CDC-NCM设备，我们挂载debugfs查看
T: Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 5 Spd=480 MxCh= 0
D: Ver= 2.00 Cls=02(comm.) Sub=00 Prot=00 MxPS=64 #Cfgs= 1
P: Vendor=0525 ProdID=a4a1 Rev= 4.09
S: Manufacturer=Linux 4.9.37 with 2b000000.usb
S: Product=NCM Gadget
C:* #Ifs= 2 Cfg#= 1 Atr=c0 MxPwr= 2mA
A: FirstIf#= 0 IfCount= 2 Cls=02(comm.) Sub=0d Prot=00
I:* If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=0d Prot=00 Driver=cdc_ncm
E: Ad=82(I) Atr=03(Int.) MxPS= 16 Ivl=32ms
I: If#= 1 Alt= 0 #EPs= 0 Cls=0a(data ) Sub=00 Prot=01 Driver=cdc_ncm
I:* If#= 1 Alt= 1 #EPs= 2 Cls=0a(data ) Sub=00 Prot=01 Driver=cdc_ncm
E: Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
通过这两行查看跟前面的三个参数对应上了（FirstIF == first interface）
A: FirstIf#= 0 IfCount= 2 Cls=02(comm.) Sub=0d Prot=00
I:* If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=0d Prot=00 Driver=cdc_ncm
usb_device_id总结用法
总的来说，可以自己一个成员变量的一个成员变量的去填充usb_device_id这个结构体，也可以借助内核提供的宏，更加的直观。
/* 本驱动支持的USB设备列表 */
/* 实例1 借助内核的宏*/
static struct usb_device_id id_table [] = {
{ USB_DEVICE(VENDOR_ID, PRODUCT_ID) },
{ },
};
MODULE_DEVICE_TABLE (usb, id_table);
/* 实例2 手动填充成员变量 */
static struct usb_device_id id_table [] = {
{ .idVendor = 0x10D2, .match_flags = USB_DEVICE_ID_MATCH_VENDOR, },
{ },
};
MODULE_DEVICE_TABLE (usb, id_table);
