一、cat设备节点获取信息

在一些嵌入式开发中需要调试USB功能，经常会cat /sys 下的相关设备节点来查看某些信息，比如说我们可以看到 /sys/bus/usb/devices 目录有多个子目录。进入到某个子目录可以看到usb设备更加详细的信息(可以理解为设备描述符)。

1、usb设备在总线上的信息

// usb设备在总线上的信息
root@ubuntu:/sys/kernel/debug# cd /sys/bus/usb/devices
root@ubuntu:/sys/bus/usb/devices# ll
total 0
drwxr-xr-x 2 root root 0 Nov 26 21:21 ./
drwxr-xr-x 4 root root 0 Nov 26 21:21 ../
lrwxrwxrwx 1 root root 0 Nov 26 21:21 1-0:1.0 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:03.0/usb1/1-0:1.0/
lrwxrwxrwx 1 root root 0 Dec 15 23:10 1-1 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:03.0/usb1/1-1/
lrwxrwxrwx 1 root root 0 Dec 15 23:18 1-1:1.0 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:03.0/usb1/1-1/1-1:1.0/
lrwxrwxrwx 1 root root 0 Nov 26 21:21 2-0:1.0 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb2/2-0:1.0/
lrwxrwxrwx 1 root root 0 Nov 26 21:21 2-1 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb2/2-1/
lrwxrwxrwx 1 root root 0 Nov 26 21:21 2-1:1.0 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb2/2-1/2-1:1.0/
lrwxrwxrwx 1 root root 0 Nov 26 21:21 2-2 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb2/2-2/
lrwxrwxrwx 1 root root 0 Nov 26 21:21 2-2:1.0 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb2/2-2/2-2:1.0/
lrwxrwxrwx 1 root root 0 Nov 26 21:21 usb1 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:03.0/usb1/
lrwxrwxrwx 1 root root 0 Nov 26 21:21 usb2 -> ../../../devices/pci0000:00/0000:00:11.0/0000:02:00.0/usb2/
 
 

 
 

其中 usbx/第x个总线，x-y:a.b/的目录格式，x表示总线号，y表示端口，a表示配置，b表示接口。
具体解释可以参照如下：

The names that begin with "usb" refer to USB controllers. More accurately, they refer to the "root hub" associated with each controller. The number is the USB bus number. In the example there is only one controller, so its bus is number 1. Hence the name "usb1".
"1-0:1.0" is a special case. It refers to the root hub's interface. This acts just like the interface in an actual hub an almost every respect; see below.
All the other entries refer to genuine USB devices and their interfaces. The devices are named by a scheme like this:
    bus-port.port.port ...
In other words, the name starts with the bus number followed by a '-'. Then comes the sequence of port numbers for each of the intermediate hubs along the path to the device.
For example, "1-1" is a device plugged into bus 1, port 1. It happens to be a hub, and "1-1.3" is the device plugged into port 3 of that hub. That device is another hub, and "1-1.3.1" is the device plugged into its port 1.
The interfaces are indicated by suffixes having this form:
    :config.interface
That is, a ':' followed by the configuration number followed by '.' followed by the interface number. In the above example, each of the devices is using configuration 1 and this configuration has only a single interface, number 0. So the interfaces show up as;
    1-1:1.0     1-1.3:1.0       1-1.3.1:1.0
A hub will never have more than a single interface; that's part of the USB spec. But other devices can and do have multiple interfaces (and sometimes multiple configurations). Each interface gets its own entry in sysfs and can have its own driver.
 
 

 
 

2、特定设备的详细信息

进入到某个目录中去，可以看到该设备的详细信息，可用cat命令获取信息。

// usb设备的详细信息
root@ubuntu:/sys/bus/usb/devices/usb1# ll
total 0
drwxr-xr-x  6 root root     0 Nov 26 21:21 ./
drwxr-xr-x  4 root root     0 Nov 26 21:21 ../
drwxr-xr-x 10 root root     0 Nov 26 21:21 1-0:1.0/
drwxr-xr-x  5 root root     0 Dec 15 23:10 1-1/
-rw-r--r--  1 root root  4096 Dec 15 23:40 authorized
-rw-r--r--  1 root root  4096 Dec 15 23:40 authorized_default
-rw-r--r--  1 root root  4096 Dec 15 23:40 avoid_reset_quirk
-r--r--r--  1 root root  4096 Nov 26 21:21 bcdDevice
-rw-r--r--  1 root root  4096 Nov 26 21:21 bConfigurationValue
-r--r--r--  1 root root  4096 Nov 26 21:21 bDeviceClass
-r--r--r--  1 root root  4096 Nov 26 21:21 bDeviceProtocol
-r--r--r--  1 root root  4096 Nov 26 21:21 bDeviceSubClass
-r--r--r--  1 root root  4096 Dec 15 23:40 bmAttributes
-r--r--r--  1 root root  4096 Dec 15 23:40 bMaxPacketSize0
-r--r--r--  1 root root  4096 Dec 15 23:40 bMaxPower
-r--r--r--  1 root root  4096 Dec 15 23:40 bNumConfigurations
-r--r--r--  1 root root  4096 Dec 15 23:40 bNumInterfaces
-r--r--r--  1 root root  4096 Nov 26 21:21 busnum
-r--r--r--  1 root root  4096 Dec 15 23:40 configuration
-r--r--r--  1 root root 65553 Nov 26 21:21 descriptors
-r--r--r--  1 root root  4096 Dec 15 23:40 dev
-r--r--r--  1 root root  4096 Nov 26 21:21 devnum
-r--r--r--  1 root root  4096 Dec 15 23:40 devpath
lrwxrwxrwx  1 root root     0 Nov 27 20:06 driver -> ../../../../../bus/usb/drivers/usb/
drwxr-xr-x  3 root root     0 Dec 15 23:40 ep_00/
-r--r--r--  1 root root  4096 Nov 26 21:21 idProduct
-r--r--r--  1 root root  4096 Nov 26 21:21 idVendor
-r--r--r--  1 root root  4096 Dec 15 23:40 ltm_capable
-r--r--r--  1 root root  4096 Nov 26 21:21 manufacturer
-r--r--r--  1 root root  4096 Dec 15 23:40 maxchild
drwxr-xr-x  2 root root     0 Nov 26 21:21 power/
-r--r--r--  1 root root  4096 Nov 26 21:21 product
-r--r--r--  1 root root  4096 Dec 15 23:40 quirks
-r--r--r--  1 root root  4096 Nov 26 21:21 removable
--w-------  1 root root  4096 Dec 15 23:40 remove
-r--r--r--  1 root root  4096 Nov 26 21:21 serial
-r--r--r--  1 root root  4096 Nov 26 21:21 speed
lrwxrwxrwx  1 root root     0 Nov 26 21:21 subsystem -> ../../../../../bus/usb/
-rw-r--r--  1 root root  4096 Nov 26 21:21 uevent
-r--r--r--  1 root root  4096 Dec 15 23:40 urbnum
-r--r--r--  1 root root  4096 Dec 15 23:40 version
 
 

 
 

二、使用debugfs

1、挂载 debugfs 到 /sys/kernel/debug 路径下

root@ubuntu:mount -t debugfs none /sys/kernel/debug
 
 

 
 

2、执行上述步骤之后，在 /sys/kernel/debug 就会生成如下的文件

root@ubuntu:/sys/bus/usb/devices# cd /sys/kernel/debug/
root@ubuntu:/sys/kernel/debug# ll
total 0
drwx------ 22 root root 0 Nov 26 21:21 ./
drwxr-xr-x  7 root root 0 Nov 26 21:21 ../
drwxr-xr-x  2 root root 0 Nov 26 21:21 acpi/
drwxr-xr-x 32 root root 0 Dec  4 16:30 bdi/
drwxr-xr-x  2 root root 0 Nov 26 21:21 bluetooth/
drwxr-xr-x  2 root root 0 Nov 26 21:21 cleancache/
drwxr-xr-x  2 root root 0 Nov 26 21:21 dma_buf/
drwxr-xr-x  4 root root 0 Nov 26 21:21 dri/
drwxr-xr-x  2 root root 0 Nov 26 21:21 dynamic_debug/
drwxr-xr-x  2 root root 0 Nov 26 21:21 extfrag/
drwxr-xr-x  2 root root 0 Nov 26 21:21 frontswap/
-r--r--r--  1 root root 0 Nov 26 21:21 gpio
drwxr-xr-x  3 root root 0 Nov 26 21:21 hid/
drwxr-xr-x  2 root root 0 Nov 26 21:21 kprobes/
drwxr-xr-x  3 root root 0 Nov 26 21:21 kvm-guest/
drwxr-xr-x  2 root root 0 Nov 26 21:21 mce/
drwxr-xr-x  2 root root 0 Nov 26 21:21 pinctrl/
-r--r--r--  1 root root 0 Nov 26 21:21 pwm
drwxr-xr-x  2 root root 0 Nov 26 21:21 regmap/
drwxr-xr-x  3 root root 0 Nov 26 21:21 regulator/
-rw-r--r--  1 root root 0 Nov 26 21:21 sched_features
-r--r--r--  1 root root 0 Nov 26 21:21 sleep_time
-r--r--r--  1 root root 0 Nov 26 21:21 suspend_stats
drwxr-xr-x  7 root root 0 Nov 26 21:21 tracing/
drwxr-xr-x  3 root root 0 Nov 26 21:21 usb/
drwxr-xr-x  2 root root 0 Nov 26 21:21 virtio-ports/
-r--r--r--  1 root root 0 Nov 26 21:21 vmmemctl
-r--r--r--  1 root root 0 Nov 26 21:21 wakeup_sources
drwxr-xr-x  2 root root 0 Nov 26 21:21 x86/
 
 

 
 

3、cat 设备节点

执行下述命令之后会以特定格式打印目前USB总线上所有USB设备的信息如下：

root@ubuntu:/sys/kernel/debug# cat usb/devices 

T:  Bus=02 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12   MxCh= 2
B:  Alloc= 17/900 us ( 2%), #Int=  1, #Iso=  0
D:  Ver= 1.10 Cls=09(hub  ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=1d6b ProdID=0001 Rev= 3.13
S:  Manufacturer=Linux 3.13.0-32-generic uhci_hcd
S:  Product=UHCI Host Controller
S:  SerialNumber=0000:02:00.0
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   2 Ivl=255ms

T:  Bus=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=12   MxCh= 0
D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=0e0f ProdID=0003 Rev= 1.03
S:  Manufacturer=VMware
S:  Product=VMware Virtual USB Mouse
C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=02 Driver=usbhid
E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=1ms

T:  Bus=02 Lev=01 Prnt=01 Port=01 Cnt=02 Dev#=  3 Spd=12   MxCh= 7
D:  Ver= 1.10 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=0e0f ProdID=0002 Rev= 1.00
S:  Product=VMware Virtual USB Hub
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   1 Ivl=255ms

T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=480  MxCh= 6
B:  Alloc=  0/800 us ( 0%), #Int=  1, #Iso=  0
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=1d6b ProdID=0002 Rev= 3.13
S:  Manufacturer=Linux 3.13.0-32-generic ehci_hcd
S:  Product=EHCI Host Controller
S:  SerialNumber=0000:02:03.0
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=  0mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   4 Ivl=256ms

T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  7 Spd=480  MxCh= 0
D:  Ver= 2.00 Cls=ff(vend.) Sub=ff Prot=ff MxPS=64 #Cfgs=  1
P:  Vendor=0bda ProdID=0129 Rev=39.60
S:  Manufacturer=Generic
S:  Product=USB2.0-CRW
S:  SerialNumber=20100201396000000
C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=500mA
I:* If#= 0 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=06 Prot=50 Driver=rts5139
E:  Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=83(I) Atr=03(Int.) MxPS=   3 Ivl=64ms
 
 

 
 

至于信息的详细解析可以参照 Linux源代码中 Documentation/usb/proc_usb_info.txt 文件。现摘录其中对该格式的详细解释：

Each line is tagged with a one-character ID for that line:

T = Topology (etc.)
B = Bandwidth (applies only to USB host controllers, which are
    virtualized as root hubs)
D = Device descriptor info.
P = Product ID info. (from Device descriptor, but they won't fit
    together on one line)
S = String descriptors.
C = Configuration descriptor info. (* = active configuration)
I = Interface descriptor info.
E = Endpoint descriptor info.

Legend:
  d = decimal number (may have leading spaces or 0's)
  x = hexadecimal number (may have leading spaces or 0's)
  s = string


Topology info:

T:  Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd
|   |      |      |       |       |      |        |        |__MaxChildren
|   |      |      |       |       |      |        |__Device Speed in Mbps
|   |      |      |       |       |      |__DeviceNumber
|   |      |      |       |       |__Count of devices at this level
|   |      |      |       |__Connector/Port on Parent for this device
|   |      |      |__Parent DeviceNumber
|   |      |__Level in topology for this bus
|   |__Bus number
|__Topology info tag

    Speed may be:
        1.5 Mbit/s for low speed USB
    12  Mbit/s for full speed USB
    480 Mbit/s for high speed USB (added for USB 2.0);
          also used for Wireless USB, which has no fixed speed
    5000    Mbit/s for SuperSpeed USB (added for USB 3.0)

    For reasons lost in the mists of time, the Port number is always
    too low by 1.  For example, a device plugged into port 4 will
    show up with "Port=03".

Bandwidth info:
B:  Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd
|   |                       |         |__Number of isochronous requests
|   |                       |__Number of interrupt requests
|   |__Total Bandwidth allocated to this bus
|__Bandwidth info tag

    Bandwidth allocation is an approximation of how much of one frame
    (millisecond) is in use.  It reflects only periodic transfers, which
    are the only transfers that reserve bandwidth.  Control and bulk
    transfers use all other bandwidth, including reserved bandwidth that
    is not used for transfers (such as for short packets).

    The percentage is how much of the "reserved" bandwidth is scheduled by
    those transfers.  For a low or full speed bus (loosely, "USB 1.1"),
    90% of the bus bandwidth is reserved.  For a high speed bus (loosely,
    "USB 2.0") 80% is reserved.


Device descriptor info & Product ID info:

D:  Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx

where
D:  Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd
|   |        |             |      |       |       |__NumberConfigurations
|   |        |             |      |       |__MaxPacketSize of Default Endpoint
|   |        |             |      |__DeviceProtocol
|   |        |             |__DeviceSubClass
|   |        |__DeviceClass
|   |__Device USB version
|__Device info tag #1

where
P:  Vendor=xxxx ProdID=xxxx Rev=xx.xx
|   |           |           |__Product revision number
|   |           |__Product ID code
|   |__Vendor ID code
|__Device info tag #2


String descriptor info:

S:  Manufacturer=ssss
|   |__Manufacturer of this device as read from the device.
|      For USB host controller drivers (virtual root hubs) this may
|      be omitted, or (for newer drivers) will identify the kernel
|      version and the driver which provides this hub emulation.
|__String info tag

S:  Product=ssss
|   |__Product description of this device as read from the device.
|      For older USB host controller drivers (virtual root hubs) this
|      indicates the driver; for newer ones, it's a product (and vendor)
|      description that often comes from the kernel's PCI ID database.
|__String info tag

S:  SerialNumber=ssss
|   |__Serial Number of this device as read from the device.
|      For USB host controller drivers (virtual root hubs) this is
|      some unique ID, normally a bus ID (address or slot name) that
|      can't be shared with any other device.
|__String info tag



Configuration descriptor info:

C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA
| | |       |       |      |__MaxPower in mA
| | |       |       |__Attributes
| | |       |__ConfiguratioNumber
| | |__NumberOfInterfaces
| |__ "*" indicates the active configuration (others are " ")
|__Config info tag

    USB devices may have multiple configurations, each of which act
    rather differently.  For example, a bus-powered configuration
    might be much less capable than one that is self-powered.  Only
    one device configuration can be active at a time; most devices
    have only one configuration.

    Each configuration consists of one or more interfaces.  Each
    interface serves a distinct "function", which is typically bound
    to a different USB device driver.  One common example is a USB
    speaker with an audio interface for playback, and a HID interface
    for use with software volume control.


Interface descriptor info (can be multiple per Config):

I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss
| | |      |      |       |             |      |       |__Driver name
| | |      |      |       |             |      |          or "(none)"
| | |      |      |       |             |      |__InterfaceProtocol
| | |      |      |       |             |__InterfaceSubClass
| | |      |      |       |__InterfaceClass
| | |      |      |__NumberOfEndpoints
| | |      |__AlternateSettingNumber
| | |__InterfaceNumber
| |__ "*" indicates the active altsetting (others are " ")
|__Interface info tag

    A given interface may have one or more "alternate" settings.
    For example, default settings may not use more than a small
    amount of periodic bandwidth.  To use significant fractions
    of bus bandwidth, drivers must select a non-default altsetting.

    Only one setting for an interface may be active at a time, and
    only one driver may bind to an interface at a time.  Most devices
    have only one alternate setting per interface.


Endpoint descriptor info (can be multiple per Interface):

E:  Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss
|   |        |            |         |__Interval (max) between transfers
|   |        |            |__EndpointMaxPacketSize
|   |        |__Attributes(EndpointType)
|   |__EndpointAddress(I=In,O=Out)
|__Endpoint info tag

    The interval is nonzero for all periodic (interrupt or isochronous)
    endpoints.  For high speed endpoints the transfer interval may be
    measured in microseconds rather than milliseconds.