USB overview

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本文提供有关 Linux® USB框架的信息
它举例说明了如何激活USB接口，以及如何从用户空间访问它。

Framework purpose

USB（通用串行总线）Linux®框架支持多种类型的：

  • 主机控制器和外围设备
  • 在外围设备中使用的小工具驱动程序和类

Linux可以在主机上使用。 在这种情况下，可以插入各种类型的外围设备，例如：

  • 大容量存储（硬盘驱动器，USB记忆棒..）
  • HID（键盘，鼠标..）

使用小工具驱动程序，Linux也可以用作外围设备。 在这种情况下，它可以充当：

  • USB大容量存储（例如，导出某些分区，文件系统）
  • 以太网卡
  • 串口
  • ...

System overview

USB controller driver USB controller driver OTG internal peripheral USBH internal peripheral USBPHYC internal peripheral USB Gadget USB Host-Side
USB Implementation architecture

Component description

  • USB用户空间（'用户空间）
    • “Host-Side”用户区
    - libusb[1]是一个Userland库，可提供对USB设备的访问。
    - usbutils[2] 是一组USB实用程序，用于收集有关连接到USB主机的USB设备的信息。 注意usbutils取决于libusb。
    - 众所周知的实用程序之一是lsusb，它用于显示有关USB总线及其连接的设备的信息。
    • Gadget 用户群
    - libusbg[3] 是一个Userland库，它提供了使用configfs API创建和解析USB小工具设备的例程。
    - |}} Gadget configfs 提供通过用户终端可用的配置界面，用于配置USB小工具。
    • 公共用户区
    - 'sysfs提供了一个可通过用户终端使用的信息界面。 请参见 How to monitor with sysfs below.
    - debugfs提供了一个调试界面，可通过用户终端使用。 请参见 How to monitor with debugfs .
  • USB framework (内核空间): 由两部分组成，即USB“主机侧”和USB“小配件”，它们依赖于具有特定 APIs 以支持USB主机和设备控制器
    • 主机端为类驱动程序提供API接口，并将请求从类驱动程序转发到主机控制器驱动程序。
    • Gadget需要外围控制器和小工具驱动程序才能使用。
  • USB hardware controllers (硬件)

USB控制器，例如 STM32 USBH internal peripheral和 STM32 OTG internal peripheral, 使用片上高速UTMI + PHY（STM32 USBPHYC internal peripheral)），或用于STM32 OTG internal peripheral的片上全速PHY。

  • USB devices (External USB devices)
    • USB OTG specification[4] defines two roles for USB devices: A-Device and B-Device. STM32 OTG controller, depending on the USB connector which is used, can accept both A-Device and B-Device, while STM32 USBH Host controller only manages B-Device:
    - A-Device is a power supplier acting as a USB Host (e.g. a PC)
    - B-Device is a power consumer and acts as a USB Peripheral (e.g. a USB key).

API description

See USB kernel documentation for more details on API functions.

Configuration

Kernel configuration

USB support, STM32 USBH driver and STM32 OTG driver are activated by default in ST deliveries. Nevertheless, if a specific configuration is required, this section indicates how the USB framework can be activated/deactivated in the kernel.

Activate USB support (CONFIG_USB=y) in the kernel configuration with the Linux Menuconfig tool: Menuconfig or how to configure kernel then select: 

Device Drivers  --->
 [*] USB support  --->

Then activate USB controllers drivers.

To activate the STM32 USBH driver, select: 

Device Drivers  --->
   --- USB support
   <*>   Support for Host-side USB
   <*>   EHCI HCD (USB 2.0) support
   <*>     Generic EHCI driver for a platform device
   <*>   OHCI HCD (USB 1.1) support
   <*>     Generic OHCI driver for a platform device

To activate the STM32 OTG driver, select: 

Device Drivers  --->
   --- USB support
   <*>   Support for Host-side USB
   <*>   USB Gadget Support  --->
   <*>   DesignWare USB2 DRD Core Support
           DWC2 Mode Selection (Dual Role mode)  --->

Then to activate the STM32 USBPHYC driver, select: 

PHY Subsystem  --->
  -*- PHY Core
  <*> STMicroelectronics STM32 USB HS PHY Controller driver

Device tree configuration

Detailed DT configurations for STM32 USB internal peripherals:

How to use the framework

How to list USB devices

lsusb displays information about the attached USB buses and devices.
In the example above, we have an onboard hub, a USB mouse and USB keyboard plugged into the hub.

Board $> lsusb							/* root hubs correspond to STM32 USB controllers (USBH,  OTG) */
Bus 002 Device 005: ID 413c:2003 Dell Computer Corp. Keyboard
Bus 002 Device 004: ID 046d:c016 Logitech, Inc. Optical Wheel Mouse
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 002: ID 0424:2514 Standard Microsystems Corp. USB 2.0 Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Board $> lsusb -t 	 	 	 	 	 	/* lsusb -t shows the USB class, the driver used and the number of ports and speed of each USB devices */
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-platform/2p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/4p, 480M
        |__ Port 1: Dev 5, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
        |__ Port 3: Dev 4, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc2/1p, 480M

To limit lsusb to the USB keyboard: 

Board $> lsusb -s 002:005 	 				/* lsusb -s [Bus]:[Device] */
Bus 002 Device 005: ID 413c:2003 Dell Computer Corp. Keyboard
Board $> lsusb -d 413c:2003  	 			 	/* lsusb -d [ID] */
Bus 002 Device 005: ID 413c:2003 Dell Computer Corp. Keyboard

To limit lsusb to the USB keyboard and display its descriptors: 

Board $> lsusb -D /dev/bus/usb/002/005  	 		/* lsusb -D /dev/bus/usb/[Bus]/[Device] */
Device: ID 413c:2003 Dell Computer Corp. Keyboard
Device Descriptor:
 ...

How to mount a USB key (mass-storage) 

Board $> mkdir /usb
Board $> mount /dev/sdxx /usb

How to configure USB Gadget through configfs

See USB gadget configfs documentation for an introduction to USB gadget configfs structure and how to use it to configure Linux USB Gadget.

Here is an example to configure USB Gadget through configfs to use the OTG as a USB Ethernet Gadget with Remote NDIS (RNDIS). See: stm32_usbotg_eth_config.sh.

How to trace and debug the framework

How to monitor

How to monitor with debugfs

Please refer to the USB devices chapter[5] to decode the output. 

Board $> cat /sys/kernel/debug/usb/devices

T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=480  MxCh= 1
B:  Alloc=  0/800 us ( 0%), #Int=  0, #Iso=  0
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=01 MxPS=64 #Cfgs=  1
P:  Vendor=1d6b ProdID=0002 Rev= 4.14
S:  Manufacturer=Linux 4.14.0 dwc2_hsotg
S:  Product=DWC OTG Controller
S:  SerialNumber=49000000.usb-otg
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#=  4 Spd=480  MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=05e3 ProdID=0723 Rev=94.54
S:  Manufacturer=Generic 
S:  Product=USB Storage
C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=500mA
I:* If#= 0 Alt= 0 #EPs= 2 Cls=08(stor.) Sub=06 Prot=50 Driver=usb-storage
E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms

T:  Bus=02 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=480  MxCh= 2
B:  Alloc=  0/800 us ( 0%), #Int=  2, #Iso=  0
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=1d6b ProdID=0002 Rev= 4.14
S:  Manufacturer=Linux 4.14.0 ehci_hcd
S:  Product=EHCI Host Controller
S:  SerialNumber=5800d000.usbh-ehci
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=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=480  MxCh= 4
D:  Ver= 2.00 Cls=09(hub  ) Sub=00 Prot=02 MxPS=64 #Cfgs=  1
P:  Vendor=0424 ProdID=2514 Rev= b.b3
C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=  2mA
I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=01 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   1 Ivl=256ms
I:* If#= 0 Alt= 1 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=02 Driver=hub
E:  Ad=81(I) Atr=03(Int.) MxPS=   1 Ivl=256ms

T:  Bus=02 Lev=02 Prnt=02 Port=03 Cnt=01 Dev#=  5 Spd=1.5  MxCh= 0
D:  Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
P:  Vendor=413c ProdID=2003 Rev= 1.00
S:  Manufacturer=Dell
S:  Product=Dell USB Keyboard
C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr= 70mA
I:* If#= 0 Alt= 0 #EPs= 1 Cls=03(HID  ) Sub=01 Prot=01 Driver=usbhid
E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=24ms

How to monitor with sysfs

USB buses monitoring with sysfs

Please refer to What are the sysfs structures for Linux USB?[6]. 

Board $> ls /sys/bus/usb/devices/
1-0:1.0  1-1  1-1:1.0  2-0:1.0  2-1  2-1.4  2-1.4:1.0  2-1:1.0  usb1  usb2

The names that begin with usb refer to USB controllers.

The device naming scheme is the following:

  • bus-port.port.port... (1-1, 2-1, or 2-1.4 in the example above)

The interfaces are indicated by suffixes in the following form:

  • :config.interface (1-1:1.0, 2-1:1.0, 2-1.4:1.0 in the example above)

Each interface corresponds to an entry in sysfs and can have its own driver.

USB Gadget monitoring with sysfs

Once the USB Gadget is configured, USB Device Controller sysfs is populated. See Documentation/ABI/stable/sysfs-class-udc| |}} Documentation/ABI/stable/sysfs-class-udc for a description of each file. 

Board $> ls /sys/class/udc/49000000.usb-otg/
a_alt_hnp_support  device           is_selfpowered  srp
a_hnp_support      function         maximum_speed   state
b_hnp_enable       is_a_peripheral  power           subsystem
current_speed      is_otg           soft_connect    uevent

How to trace

How to trace with usbmon

usbmon [7] collects traces of the input/output on the USB bus.
It relies on a kernel part and on a user part, and reports the requests made by USB device drivers to the Host controller drivers.
Activate USBMON support (CONFIG_USB_MON=y) in the kernel configuration with Linux Menuconfig tool: Menuconfig or how to configure kernel.
A usbmon entry is created in debugfs. It includes several files.
The file names consist of a number (the USB bus - 0 relates to all buses) and a letter (s, u or t). The s file contains a generic event overview. The t (deprecated) and u files will stream trace data.
To gather debug data, either use the master file 0u (to capture data from all devices) or find out the bus to which your device is connected and use the corresponding bus file. For example, if the device is connected to bus 1: 

Board $> cat /sys/kernel/debug/usb/usbmon>1u > bus1data.log

To stop the capture, just type (CTRL+C) to kill the command. You can then analyze the log with vUSBAnalyzer graphical tool on your Linux host.

How to trace using a protocol analyzer

A USB protocol analyzer is a USB traffic sniffer that decodes USB descriptors and displays bus states and packets sent. Refer to you USB protocol analyzer user manual.

How to debug

Activating USB framework debug messages

A detailed dynamic trace is available in How to use the kernel dynamic debug

 Board $> echo  "file usb* +p" > /sys/kernel/debug/dynamic_debug/control

This command enables all the traces related to the USB core and drivers at runtime.
A finer selection can be made by choosing only the files to trace.

Info.png Reminder: loglevel needs to be increased to 8 either by using boot arguments or by sending the dmesg -n 8 command from the console

EHCI/OHCI driver debugfs entry

EHCI/OHCI drivers export a debugfs entry when CONFIG_DYNAMIC_DEBUG is enabled. 

Board $> ls /sys/kernel/debug/usb/ohci/5800c000.usbh-ohci/
async  periodic  registers
Board $> ls /sys/kernel/debug/usb/ehci/5800d000.usbh-ehci/
async  bandwidth  periodic  registers
  • async dumps a snapshot of the async schedule.
  • bandwith dumps the bandwidth allocation
  • periodic dumps a snapshot of the periodic schedule.
  • registers dumps the USB controller registers

DWC2 driver debug messages and debugfs entry

To get the verbose messages from the DWC2 driver used by STM32 OTG, activate "Enable Debugging Messages" in the Linux kernel via the menuconfig Menuconfig or how to configure kernel.

Device Drivers  --->
   [*] USB support
   <*>   Support for Host-side USB
   <*>   USB Gadget Support  --->
   <*>   DesignWare USB2 DRD Core Support
   [*]     Enable Debugging Messages
   [*]       Enable Verbose Debugging Messages
   [ ]     Enable Missed SOF Tracking
   [*]     Enable Debugging Messages For Periodic Transfers

This can be done manually in your kernel .config file: 

CONFIG_USB_SUPPORT=y
CONFIG_USB_DWC2=y
CONFIG_USB_DWC2_DEBUG=y
CONFIG_USB_DWC2_VERBOSE=y
CONFIG_USB_DWC2_DEBUG_PERIODIC=y

The debug support for DWC2 driver (CONFIG_USB_DWC2_DEBUG) compiles all the files located in Linux kernel drivers/usb/dwc2/| |}} drivers/usb/dwc2/ folder with DEBUG flag.

Info.png Reminder: loglevel needs to be increased to 8 by using either boot arguments or the dmesg -n 8 command through the console

The DWC2 driver also exports a debugfs entry that contains useful information: 

Board $> ls /sys/kernel/debug/49000000.usb-otg/
dr_mode  ep0  ep1in  ep1out  ep2in  ep2out  ep3in  ep3out  ep4in  ep4out  ep5in  ep5out  ep6in  ep6out  ep7in  ep7out  ep8in  ep8out  fifo  hw_params  params  regdump state  testmode
  • dr_mode indicates the working mode of the USB controller. It can be "host", "peripheral" or "otg". The value is set through a device tree property.
  • ep* files show the state of the given endpoint.
  • fifo shows the FIFO information for the overall FIFO and all the periodic transmission FIFOs.
  • hw_params shows the parameters read from USB controller registers.
  • params shows the parameters used by the driver.
  • regdump dumps all the USB controller registers.
  • state shows the overall state of the hardware controller and some general information on the available endpoints.
  • testmode shows/sets usb test mode ("test_j", "test_k", "test_se0_nak", "test_packet", "test_force_enable").

Source code location

The source files are located inside the Linux kernel.

References

  1. ↑ libusb: a cross-platform library to access USB devices
  2. ↑ usbutils: USB utilities for Linux, including lsusb
  3. ↑ libusbg: a C library encapsulating the kernel USB gadget-configfs userspace API functionality
  4. ↑ On-The-Go and Embedded Host Supplement to the USB Revision 2.0 Specification
  5. ↑ Linux USB API: The Linux-USB Host Side API - The USB devices
  6. ↑ What are the sysfs structures for Linux USB?
  7. ↑ Documentation/usb/usbmon.txt | |}} usbmon
取自“http://wiki.100ask.org/index.php?title=USB_overview&oldid=7790”