CM3 USB OTG troubles

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I'm trying to get USB OTG going on a compute module 3 (using it's CMIO evalboard). The ultimate goal would be to switch the mode dynamically. A workaround could be to decide about the personality after booting. The worst case would be a necessary change before boot (probably would whip out the good old u-boot in that case)

However the first step is to get the device going as a serial gadget, and I'm already failing miserably at that. When I insmod the relevant modules I get the dreaded "can't find an available UDC" error:

I do *not* run a raspibian, but a custom system based on OpenADK (think buildroot).

The relevant files follow:

Code: Select all

kernel=kernel
dtparam=audio,i2s,spi,i2c
device_tree=bcm2710-rpi-cm3.dtb
start_file=start.elf
fixup_file=fixup.dat
gpu_mem=16
dtoverlay=dwc-otg.dtb
dtoverlay=dwc2.dtb

vcdbg log msg output: https://pastebin.com/JRiPQta7

dmesg output for boot (prior to any module loading): https://pastebin.com/tuxwXE88

kernel 4.14.0 config: https://pastebin.com/R47aGSSV

insmod-statements:

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root@box:~ # insmod /lib/modules/4.14.0-1/udc-core.ko
root@box:~ # insmod /lib/modules/4.14.0-1/libcomposite.ko
root@box:~ # insmod /lib/modules/4.14.0-1/u_serial.ko
root@box:~ # insmod /lib/modules/4.14.0-1/usb_f_acm.ko
root@box:~ # insmod /lib/modules/4.14.0-1/g_serial.ko

dmesg output after loading:

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[  476.468226] userial_init: registered 4 ttyGS* devices
[  484.447683] udc-core: couldn't find an available UDC - added [g_serial] to list of pending drivers

Any pointers to what's going on are very much appreciated. I'm probably an idiot, but also kinda out of ideas right now.