Here you have the dmesg | grep tty return
[ 23.562827] Couldn't install MOXA Smartio/Industio family tty driver !
[ 23.625082] SyncLink serial driver $Revision: 4.38 $, tty major#254
[ 23.694525] SyncLink MultiPort driver $Revision: 4.38 $, tty major#253
[ 23.694677] SyncLink GT $Revision: 4.36 $, tty major#252
[ 23.757959] 00:0c: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
As you can see, it says that can't install the moxa driver... I google it and found that the driver is mxser.c, but I tried to modprobe it and doesnt' work, I don't know how to compile it... or where it is on the make menuconfig...