SB Gadget Serial (g_serial) not working on Noble 6.12.51 build NanoPi Duo

[sgjava]

I built an unofficial Armbian 6.12.51 (Noble) image using the build tool:

 

Armbian-unofficial_25.11.0-trunk_Nanopiduo_noble_current_6.12.51.img

 

I am trying to get the micro-USB port to work as a USB serial gadget (g_serial / libcomposite).

 

What I have done / observed:

 

g_serial and libcomposite modules are loaded:

lsmod | grep g_serial g_serial 12288 0 libcomposite 49152 2 g_serial,usb_f_acm

 

ConfigFS is mounted:

mount | grep configfs configfs on /sys/kernel/config type configfs (rw,nosuid,nodev,noexec,relatime)

 

UDC exists:

ls /sys/class/udc/ musb-hdrc.2.auto

 

Gadget folder does not exist:

ls /sys/kernel/config/usb_gadget/ # output: empty

 

Trying to manually bind a gadget fails:

echo musb-hdrc.2.auto | sudo tee /sys/kernel/config/usb_gadget/g1/UDC # Output: tee: UDC: Device or resource busy

 

Current UDC mode:

cat /sys/class/udc/musb-hdrc.2.auto/device/mode b_idle

 

There is no /sys/class/usb_role/usb0/role available to force device mode.

 

This setup works fine on Jammy kernel, same cable, same SD card rootfs.

 

Problem:

 

The OTG controller comes up in b_idle mode, preventing the USB gadget from binding. /dev/ttyACM0 never appears on the host PC. It seems like the device tree / overlay for Noble 6.12.51 is not configuring the OTG port for peripheral mode.

 

What I want:

 

USB serial gadget (g_serial) working over the micro-USB port on Noble 6.12.51 build.

Any advice on the correct overlay or device tree modification needed to bring the OTG port into device mode at boot.

 

Extra info:

CONFIG_USB_CONFIGFS_SERIAL=y in kernel

CONFIG_USB_LIBCOMPOSITE compiled as module

Micro-USB cable confirmed working with Jammy kernel

Modules: libcomposite, g_serial, usb_f_acm present

 

Thanks in advance for guidance!