Custom board with TI AM3359 - /proc/bus/usb empty, no USB devices

Hi there,

here I have a custom board based on am TI am3359. The TI Sitara SDK 05.05.01.00 is used for porting U-Boot and the Linux kernel. So far, the kernel is booting and I can access the SD card for the rootfs. Now I'm trying to get USB support, but this isn't working yet.

The first thing I didn't quite understand is the folder /proc/bus/usb - it is empty. However, there is a usbfs entry in my fstab:

usbfs                /proc/bus/usb        usbfs      defaults              0  0

USB support for the kernel also seems to be active:

root@am335x-evm:/proc# zcat config.gz |grep -i usb|grep -v ^#
CONFIG_USB_USBNET=y
CONFIG_USB_NET_CDCETHER=y
CONFIG_USB_NET_CDC_EEM=y
CONFIG_USB_NET_CDC_NCM=y
CONFIG_USB_NET_DM9601=y
CONFIG_USB_ZD1201=y
CONFIG_V4L_USB_DRIVERS=y
CONFIG_USB_VIDEO_CLASS=y
CONFIG_USB_VIDEO_CLASS_INPUT_EVDEV=y
CONFIG_SND_USB=y
CONFIG_SND_USB_AUDIO=y
CONFIG_USB_HID=y
CONFIG_USB_SUPPORT=y
CONFIG_USB_COMMON=y
CONFIG_USB_ARCH_HAS_HCD=y
CONFIG_USB_ARCH_HAS_OHCI=y
CONFIG_USB_ARCH_HAS_EHCI=y
CONFIG_USB=y
CONFIG_USB_ANNOUNCE_NEW_DEVICES=y
CONFIG_USB_DEVICEFS=y
CONFIG_USB_DEVICE_CLASS=y
CONFIG_USB_SUSPEND=y
CONFIG_USB_OTG=y
CONFIG_USB_MUSB_HDRC=y
CONFIG_USB_MUSB_TI81XX_GLUE=y
CONFIG_USB_MUSB_TI81XX=y
CONFIG_MUSB_PIO_ONLY=y
CONFIG_USB_STORAGE=y
CONFIG_USB_GADGET=y
CONFIG_USB_GADGET_VBUS_DRAW=2
CONFIG_USB_GADGET_STORAGE_NUM_BUFFERS=2
CONFIG_USB_GADGET_MUSB_HDRC=y
CONFIG_USB_GADGET_DUALSPEED=y
CONFIG_USB_ETH=m
CONFIG_USB_ETH_RNDIS=y
CONFIG_USB_FILE_STORAGE=m
CONFIG_USB_MASS_STORAGE=m
CONFIG_USB_OTG_UTILS=y
CONFIG_NOP_USB_XCEIV=y

'lsusb' doesn't show anything (there is a USB mouse connected). I also haven't noticed any strange kernel messages while booting. USB is (hopefully) correctly activated in the board file. Do you have any hints for me? I'm not quite sure where to search next for this problem.