Switch USB role on imx6 without ID pin

[crudo]

Is it possible to switch USB roles on i.MX6 purely via SW without defining the OTG ID pin in the device tree?

I have the following device tree configuration on my board.

&usbotg1 {
    pinctrl-names = "default";
    dr_mode = "otg";
    status = "okay";
};

After I boot the board, it's operating on gadget mode (initial state) without issues. And I can switch to host mode using the command below.

echo host > /sys/kernel/debug/ci_hdrc.0/role

In host mode, everything work as expected. However, when I try to switch back to gadget mode using the same command it doesn't work anymore.

echo gadget > /sys/kernel/debug/ci_hdrc.0/role

Switching to host again, works.

Questions

• Do I necessarily need to define the USB OTG ID pin on the device tree or can I switch via software?
• Why gadget mode works once after a fresh boot?
• What happens when no ID pin is defined?

[rudi_cyber]

You can refer to the document to finish configuration and setting. 

linux-imx\Documentation\usb\chipidea.rst

The chipidea.rst has very detailed steps. 

usb id pin is no needed. Or it could not be called "role switch".

has usb id is called "otg" mode. 

linux-imx\Documentation\usb\chipidea.rst

[crudo]

Thanks for pointing me to the documentation @rudi_cyber. I added CONFIG_USB_OTG_FSM=y to the kernel config as described in https://www.kernel.org/doc/html/latest/usb/chipidea.html but I get a compilation error.

|   CC      drivers/usb/host/ehci-hcd.o
| In file included from /kernel-source/drivers/usb/chipidea/trace.h:18,
|                  from /kernel-source/drivers/usb/chipidea/trace.c:11:
| /kernel-source/drivers/usb/chipidea/ci.h: In function 'ci_otg_is_fsm_mode':
| /kernel-source/drivers/usb/chipidea/ci.h:476:47: error: dereferencing pointer to incomplete type 'struct ci_hdrc_platform_data'
|   476 |  struct usb_otg_caps *otg_caps = &ci->platdata->ci_otg_caps;
|       |                                               ^~
|   CC      drivers/usb/chipidea/host.o
| make[4]: *** [/kernel-source/scripts/Makefile.build:266: drivers/usb/chipidea/trace.o] Error 1

Do you know why that is happening? Do I need a specific kernel version or a patch?

[ajita02]

Hi,

I want to achieve USB detection without ID pin. I am getting same error while compilation. Can you provide me a lead?

Thanks,

Ajita

[Harvey021]

Hi @crudo 

You can try echo peripheral > /sys/kernel/debug/ci_hdrc.0/role. 

OTG ID PIN needs to be configured, otherwise, which mostly cause operations either in host or peripheral mode.

Best regards

Harvey

Best regards

Harvey