[openharmony] USB gadget configuration HDC function cfg file interpretation

cfg File path
https://gitee.com/openharmony/device_board_hihope/blob/master/rk3568/cfg/init.rk3568.usb.cfg
https://gitee.com/openharmony/startup_init_lite/blob/master/services/etc/init.usb.configfs.cfg

• First of all, will configfs The file system is mounted on the system
  mount configfs none /config

One 、 Create device

• Create the directory corresponding to the device ：
  mkdir /config/usb_gadget/g1 0770 shell shell
• Each device has its own product id and vendor id
  write /config/usb_gadget/g1/idVendor 0x2207
write /config/usb_gadget/g1/idProduct 0x0018
• Every device There must also be his Serial number 、 manufacturer 、 Product string , Create a string The directory is used to store this information .
  mkdir /config/usb_gadget/g1/strings/0x409 0770
copy /sys/block/mmcblk0/device/cid /config/usb_gadget/g1/strings/0x409/serialnumber
write /config/usb_gadget/g1/strings/0x409/manufacturer Rockchip
write /config/usb_gadget/g1/strings/0x409/product \"HDC Device\"

Two 、 Create a configuration

• Each device consists of many configurations , The directories corresponding to these configurations also need to be created
  mkdir /config/usb_gadget/g1/configs/b.1 0770 shell shell
• Each configuration also needs its own string , So you need to create a corresponding for each language string Catalog
  mkdir /config/usb_gadget/g1/configs/b.1/strings/0x409 0770 shell shell
• Then the configuration string can be written in
  write /config/usb_gadget/g1/configs/b.1/strings/0x409/configuration hdc
• Other properties of this configuration can also be set
  write /config/usb_gadget/g1/configs/b.1/MaxPower 500

3、 ... and 、 Create features

• The device will provide some functions , For each function, the corresponding directory must also be created
  mkdir /config/usb_gadget/g1/functions/ffs.hdc

Four 、 Associate functions with corresponding configurations

• Now a lot of devices have been created , Each device has some configurations and some functions . Next, we need to identify which functions are effective in which configuration . A function can be included in multiple configurations . The above actions are completed through symbolic links .
  symlink /config/usb_gadget/g1/functions/ffs.hdc /config/usb_gadget/g1/configs/b.1/f1

mount functionfs file system

• functionfs Think of it as a composite with unique behavior function. The main function is to mount functionfs File system directory ep0 Catalog , Used to write descriptors and strings to complete negotiation .
  mount functionfs hdc /dev/usb-ffs/hdc uid=2000,gid=2000

5、 ... and 、 Enable the device

• To enable this device, we must bind it to some udc The above to
  write /config/usb_gadget/g1/UDC ${sys.usb.controller}
  UDC The name should be directory /sys/class/udc/* One of the following .

6、 ... and 、 To enable the device

• write /config/usb_gadget/g1/UDC none

7、 ... and 、 eliminate

• Remove function from configuration
  rm /config/usb_gadget/g1/configs/b.1/f1
• Remove the string directory in the configuration ( Did not find )
  rmdir configs/<config name>.<number>/strings/<lang>
• Remove configuration （ Did not find ）
  rmdir configs/<config name>.<number>
• Remove features （ Did not find ）
  rmdir functions/<name>.<instance name>
• Remove the device string Directory ( Did not find ）
  rmdir strings/<lang>
• Finally remove the device
  rmdir <gadget name>

Implementation design

• One gadget There is it config Group , This group has some properties （idVendor, idProduct etc） And default subgroups （configs, functions, strings）.
• Write these properties , This will cause these attributes to be stored in the corresponding location . stay configs, functions, strings In the subgroup , Users can create their subgroups , Represents the corresponding configuration , Functions and strings .
• Users can create some configurations and functions , And use symbolic links to link them . On the device UDC After the attribute is written , This information will be used . This writing means that the device and the corresponding UDC It's connected .
• drivers/usb/gadget/configfs.c The code inside will facilitate all configurations , It will facilitate all functions in each configuration , And bind them .

Reference material

Linux USB gadget configured through configfs
How FunctionFS works