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lsusb 
...
Bus 006 Device 006: ID 067b:2303 Prolific Technology, Inc. PL2303 Serial Port

http://www.linux-usb.org/usb.ids

067b  Prolific Technology, Inc.
	...
	2303  PL2303 Serial Port

USB serial adapters

lsmod
ftdi_sio               27200  0
usbserial              17633  1 ftdi_sio

Correct lsmod output:

lsmod
pl2303                  6688  0
usbserial              17633  1 pl2303

opkg update 
opkg remove kmod-usb-serial-ftdi
opkg remove kmod-usb-serial-pl2303	
opkg install kmod-usb-serial-pl2303

lsmod
pl2303                  6688  0
usbserial              17633  1 pl2303