linux/Documentation/usb/chipidea.txt

1. How to test OTG FSM(HNP and SRP)
-----------------------------------
To show how to demo OTG HNP and SRP functions via sys input files
with 2 Freescale i.MX6Q sabre SD boards.

1.1 How to enable OTG FSM in menuconfig
---------------------------------------
Select CONFIG_USB_OTG_FSM, rebuild kernel Image and modules.
If you want to check some internal variables for otg fsm,
select CONFIG_USB_CHIPIDEA_DEBUG, there are 2 files which
can show otg fsm variables and some controller registers value:
cat /sys/kernel/debug/ci_hdrc.0/otg
cat /sys/kernel/debug/ci_hdrc.0/registers

1.2 Test operations
-------------------
1) Power up 2 Freescale i.MX6Q sabre SD boards with gadget class driver loaded
   (e.g. g_mass_storage).

2) Connect 2 boards with usb cable with one end is micro A plug, the other end
   is micro B plug.

   The A-device(with micro A plug inserted) should enumrate B-device.

3) Role switch
   On B-device:
   echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req

   if HNP polling is not supported, also need:
   On A-device:
   echo 0 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_req

   B-device should take host role and enumrate A-device.

4) A-device switch back to host.
   On B-device:
   echo 0 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req

   A-device should switch back to host and enumrate B-device.

5) Remove B-device(unplug micro B plug) and insert again in 10 seconds,
   A-device should enumrate B-device again.

6) Remove B-device(unplug micro B plug) and insert again after 10 seconds,
   A-device should NOT enumrate B-device.

   if A-device wants to use bus:
   On A-device:
   echo 0 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_drop
   echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_req

   if B-device wants to use bus:
   On B-device:
   echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req

7) A-device power down the bus.
   On A-device:
   echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/a_bus_drop

   A-device should disconnect with B-device and power down the bus.

8) B-device does data pulse for SRP.
   On B-device:
   echo 1 > /sys/bus/platform/devices/ci_hdrc.0/inputs/b_bus_req

   A-device should resume usb bus and enumrate B-device.

1.3 Reference document
----------------------
"On-The-Go and Embedded Host Supplement to the USB Revision 2.0 Specification
July 27, 2012 Revision 2.0 version 1.1a"