iMX8MN USB OTG role reversal

[dvlogic]

Hi,

I'm trying to dynamically configure my custom i.MX8M nano board to switch USB roles from host mode to gadget (or peripheral).  I currently have my board configured as a USB host and I'm able to enumerate a USB FTDI serial device. All works as expected.

I would like to configure the dr_mode as "otg" and setup my board to either be a host device as I have today or dynamically switch it to be a USB mass storage peripheral (gadget).

I can't find any working examples and I'm hoping someone could help me.  It seems when I configure my DTS to be dr_mode = "otg" with usb-role-switch enabled, I can't get any USB functionality to work.  If I run some USB mass storage gadget example code, the best I get is an error "udc-core: couldn't find an available UDC or it's busy"

I'm confident my USB hardware is correct since I can run the uboot "ums mmc 2" command to make my board enumerate as a mass storage USB device.  Also, as stated above, I can connect the USB to a FTDI serial port and configure it as a my DTS to be dr_mode = "host" and that works too.

I'm currently running a custom Linux build based on imx-5.10.72-2.2.0 (Yocto hardknott).  

[Dhruvit]

Hi @dvlogic,

I hope you are doing well

 If I run some USB mass storage gadget example code, the best I get is an error "udc-core: couldn't find an available UDC or it's busy"

=> Please try to add the below configuration in the kernel.

USB_G_SERIAL [=m]

Kindly refer to section 4.9 USB of i.MX Linux Reference Manual for more configuration.

If it does not solve the issue, kindly share your device tree node.

Thanks & Regards,

Dhruvit Vasavada

[dvlogic]

No the solution you posted still doesn't work for me. 

The problem I was having with udc-core was related to me adding the following config to my kernel build "CONFIG_USB_FSL_USB2" - this was a stupid cut-n-paste from some other post.

Now I am back to trying to get my device to work in gadget "peripheral" mode.  The fundamental problem is my custom hardware is designed with only a USB-A port (which is doesn't expose the USB_ID pin to the external host).  The USB_ID pin is floating on the hardware.  In addition VBus is hardwired to +5 volts.

With the driver, I am able to set the role as "host" had communicate with external USB peripherals.  However, when I set the role as gadget and program a USB gadget config, I never can get my board to enumerate to an external host. 

I'm convinced there must be a software work-around since the same hardware will enumerate as a mass storage gadget device when I boot directly to U-Boot and run the command "ums mmc 2"

Let me know if you have any thoughts on where I should look for a software work-around.

Thanks!

[dvlogic · Accepted solution]

I solved this today through a whole lot of trial and error.  

I made my DTS for usbotg as follows:

&usbotg1 {
	dr_mode = "otg";
	hnp-disable;
	srp-disable;
	adp-disable;
	disable-over-current;
	usb-role-switch;
	role-switch-default-mode = "host";
	samsung,picophy-pre-emp-curr-control = <3>;
	samsung,picophy-dc-vol-level-adjust = <7>;
	status = "okay";

	assigned-clocks = <&clk IMX8MN_CLK_USB_BUS>,
			  <&clk IMX8MN_CLK_USB_CORE_REF>;
	assigned-clock-parents = <&clk IMX8MN_SYS_PLL2_500M>,
				 <&clk IMX8MN_SYS_PLL1_100M>;
};

And then after I configured my mass_storage device in the /sys/kernel/config/usb_gadget path, I had to do the following to get it to enumerate to my host.

echo device > /sys/bus/platform/devices/ci_hdrc.0/usb_role/ci_hdrc.0-role-switch/role

The final missing thing that I want to figure out is how to know when the host has ejected/un-mounted my mass storage USB gadget so that I can take action on what was transferred from the host to my device.

[Dhruvit]

Hi @dvlogic,

I hope you are doing well

If your issue is resolved, should we close this thread?

Thanks & Regards,
Dhruvit Vasavada

[dvlogic]

Yes, I even self marked it as solved - go ahead and close!