|# modprobe dummy_hcd num=2
|# modprobe libcomposite

|# lsmod
|Module                  Size  Used by
|libcomposite           31648  0
|dummy_hcd              19871  0

|# mkdir /sys/kernel/config/usb_gadget/oha
|# cd /sys/kernel/config/usb_gadget/oha
|# mkdir configs/def.1
|# mkdir configs/def.2
|# mkdir functions/acm.ttyS1
|# mkdir strings/0x1
|mkdir: cannot create directory `strings/0x1': Invalid argument
|# mkdir strings/0x409
|# mkdir strings/1033
|mkdir: cannot create directory `strings/1033': File exists
|# mkdir strings/1032
|# mkdir configs/def.1/strings/0x409
|# mkdir configs/def.2/strings/0x409

|#find . -ls
|   975    0 drwxr-xr-x   5 root     root            0 Dec 23 17:40 .
|   978    0 drwxr-xr-x   4 root     root            0 Dec 23 17:43 ./strings
|  4100    0 drwxr-xr-x   2 root     root            0 Dec 23 17:43 ./strings/1032
|   995    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./strings/1032/serialnumber
|   996    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./strings/1032/product
|   997    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./strings/1032/manufacturer
|  2002    0 drwxr-xr-x   2 root     root            0 Dec 23 17:41 ./strings/0x409
|   998    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./strings/0x409/serialnumber
|   999    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./strings/0x409/product
|  1000    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./strings/0x409/manufacturer
|   977    0 drwxr-xr-x   4 root     root            0 Dec 23 17:41 ./configs
|  4081    0 drwxr-xr-x   3 root     root            0 Dec 23 17:41 ./configs/def.2
|  4082    0 drwxr-xr-x   3 root     root            0 Dec 23 17:42 ./configs/def.2/strings
|  2016    0 drwxr-xr-x   2 root     root            0 Dec 23 17:42 ./configs/def.2/strings/0x409
|  1001    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./configs/def.2/strings/0x409/configuration
|  1002    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./configs/def.2/bmAttributes
|  1003    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./configs/def.2/MaxPower
|   979    0 drwxr-xr-x   3 root     root            0 Dec 23 17:42 ./configs/def.1
|   980    0 drwxr-xr-x   3 root     root            0 Dec 23 17:42 ./configs/def.1/strings
|  5122    0 drwxr-xr-x   2 root     root            0 Dec 23 17:42 ./configs/def.1/strings/0x409
|  1004    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./configs/def.1/strings/0x409/configuration
|  1005    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./configs/def.1/bmAttributes
|  1006    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./configs/def.1/MaxPower
|   976    0 drwxr-xr-x   3 root     root            0 Dec 23 17:41 ./functions
|   981    0 drwxr-xr-x   2 root     root            0 Dec 23 17:41 ./functions/acm.ttyS1
|  1007    0 -r--r--r--   1 root     root         4096 Dec 23 17:43 ./functions/acm.ttyS1/port_num
|  1008    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./UDC
|  1009    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./bcdUSB
|  1010    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./bcdDevice
|  1011    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./idProduct
|  1012    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./idVendor
|  1013    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./bMaxPacketSize0
|  1014    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./bDeviceProtocol
|  1015    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./bDeviceSubClass
|  1016    0 -rw-r--r--   1 root     root         4096 Dec 23 17:43 ./bDeviceClass

|# cat functions/acm.ttyS1/port_num
|0
|# ls -lah /dev/ttyGS*
|crw-rw---T 1 root dialout 252, 0 Dec 23 17:41 /dev/ttyGS0
|
|# echo 0x1234 > idProduct
|# echo 0xabcd > idVendor
|# echo 1122 > strings/0x409/serialnumber
|# echo "The manufacturer" > strings/0x409/manufacturer
|# echo 1 > strings/1032/manufacturer
|# echo 1sa > strings/1032/product
|# echo tada > strings/1032/serialnumber
|echo "Primary configuration" > configs/def.1/strings/0x409/configuration
|# echo "Secondary configuration" > configs/def.2/strings/0x409/configuration
|# ln -s functions/acm.ttyS1 configs/def.1/
|# ln -s functions/acm.ttyS1 configs/def.2/
|find configs/def.1/ -ls
|   979    0 drwxr-xr-x   3 root     root            0 Dec 23 17:49 configs/def.1/
|  6264    0 lrwxrwxrwx   1 root     root            0 Dec 23 17:48 configs/def.1/acm.ttyS1 -> ../../../../usb_gadget/oha/functions/acm.ttyS1
|   980    0 drwxr-xr-x   3 root     root            0 Dec 23 17:42 configs/def.1/strings
|  5122    0 drwxr-xr-x   2 root     root            0 Dec 23 17:49 configs/def.1/strings/0x409
|  6284    0 -rw-r--r--   1 root     root         4096 Dec 23 17:47 configs/def.1/strings/0x409/configuration
|  6285    0 -rw-r--r--   1 root     root         4096 Dec 23 17:49 configs/def.1/bmAttributes
|  6286    0 -rw-r--r--   1 root     root         4096 Dec 23 17:49 configs/def.1/MaxPower
|
|echo 120 > configs/def.1/MaxPower
|
|# ls -lh /sys/class/udc/
|total 0
|lrwxrwxrwx 1 root root 0 Dec 23 17:50 dummy_udc.0 -> ../../devices/platform/dummy_udc.0/udc/dummy_udc.0
|lrwxrwxrwx 1 root root 0 Dec 23 17:50 dummy_udc.1 -> ../../devices/platform/dummy_udc.1/udc/dummy_udc.1
|# echo dummy_udc.0 > UDC
|# lsusb
|Bus 001 Device 002: ID abcd:1234 Unknown
|
|lsusb -d abcd:1234 -v
|Device Descriptor:
…
|  idVendor           0xabcd Unknown
|  idProduct          0x1234
|  bcdDevice            3.06
|  iManufacturer           1 The manufacturer
|  iProduct                2
|  iSerial                 3 1122
|  bNumConfigurations      2
…
|echo "" > UDC

v5…v6
- wired up strings with usb_gstrings_attach()
- add UDC attribe. Write "udc-name" will bind the gadget. Write an empty
  string (it should contain \n since 0 bytes write get optimzed away)
  will unbind the UDC from the gadget. The name of available UDCs can be
  obtained from /sys/class/udc/

v4…v5
- string rework. This will add a strings folder incl. language code like
    strings/409/manufacturer
  as suggested by Alan.
- rebased ontop reworked functions.c which has usb_function_instance
  which is used prior after "mkdir acm.instance" and can be directly
  used for configuration via configfs.

v3…v4
 - moved functions from the root folde down to the gadget as suggested
   by Michał
 - configs have now their own configs folder as suggested by Michał.
   The folder is still name.bConfigurationValue where name becomes the
   sConfiguration. Is this usefull should we just stilc
   configs/bConfigurationValue/ ?
 - added configfs support to the ACM function. The port_num attribute is
   exported by f_acm. An argument has been added to the USB alloc
   function to distinguish between "old" (use facm_configure() to
   configure and configfs interface (expose a config_node).
   The port_num is currently a dumb counter. It will
   require some function re-work to make it work.

scheduled for v5:
- sym linking function into config.

v2…v3
- replaced one ifndef by ifdef as suggested by Micahał
- strstr()/strchr() function_make as suggested by Micahł
- replace [iSerialNumber|iProduct|iManufacturer] with
  [sSerialNumber|sProduct|sManufacturer] as suggested by Alan
- added creation of config descriptors

v1…v2
- moved gadgets from configfs' root directory into /udcs/ within our
  "usb_gadget" folder. Requested by Andrzej & Michał
- use a dot as a delimiter between function's name and its instance's name
  as suggested by Michał
- renamed all config_item_type, configfs_group_operations, make_group,
  drop_item as suggested by suggested by Andrzej to remain consisten
  within this file and within other configfs users
- Since configfs.c and functions.c are now part of the udc-core module,
  the module itself is now called udc. Also added a tiny ifdef around
  init code becuase udc-core is subsys init and this is too early for
  configfs in the built-in case. In the module case, we can only have
  one init function.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>