Ben, are you using the stock kernel or an OE kernel? I think if Chris is using an OE image, it is likely that it does not include the kernel module ftdi_sio. You can list the available loadable modules with
find /lib/modules -name '*.ko'
You need both usbserial.ko (present) and ftdi_sio.ko (not present) for this to work. There is a second issue of making sure the vendor id and product id are mapped to the ftdi driver which we can ignore until the drivers are working.
FWIW I did a quick test on my silvermoon CHB; copied the kernel modules manually from the OE working files, plugged an Arduino into the USB port, and forced the driver to load as follows:
update-modules
lsusb # to get the vendor and product ID of my device
modprobe ftdi_sio vendor=0x2341 product=0x0001
The result was not good: it created TWO tty devices, and accessing the first of them causes a nasty system crash, accessing the second returns no data. However it is probably worth repeating this experiment with a cleaner OE kernel. My currently installed kernel has some non-standard USB code merged in from the Freescale source tree that might be causing problems.
For the record here are my results in detail:
>> Plug Ardino UNO into USB port:
[ 38.610000] usb 1-1.2: new full speed USB device using fsl-ehci and address 4
[ 38.720000] usb 1-1.2: configuration #1 chosen from 1 choice
>> Find the Vendor and Product Id's
root@chumby-falconwing:~# lsusb
Bus 001 Device 001: ID 1d6b:0002
Bus 001 Device 002: ID 05e3:0608
Bus 001 Device 003: ID 0718:044e
Bus 001 Device 004: ID 2341:0001 << This is the new device
>> Force the ftdi driver to load
root@chumby-falconwing:~# modprobe ftdi_sio vendor=0x2341 product=0x0001
[ 113.590000] usbcore: registered new interface driver usbserial
[ 113.600000] USB Serial support registered for generic
[ 113.600000] usbcore: registered new interface driver usbserial_generic
[ 113.620000] usbserial: USB Serial Driver core
[ 113.690000] USB Serial support registered for FTDI USB Serial Device
[ 113.690000] ftdi_sio 1-1.2:1.0: FTDI USB Serial Device converter detected
[ 113.720000] usb 1-1.2: Detected FT2232C
[ 113.740000] usb 1-1.2: FTDI USB Serial Device converter now attached to ttyUSB0
[ 113.740000] ftdi_sio 1-1.2:1.1: FTDI USB Serial Device converter detected
[ 113.800000] usb 1-1.2: Detected FT2232C
[ 113.800000] usb 1-1.2: FTDI USB Serial Device converter now attached to ttyUSB1
[ 113.870000] usbcore: registered new interface driver ftdi_sio
[ 113.870000] ftdi_sio: v1.4.3:USB FTDI Serial Converters Driver
>>> Two devices ttyUSB0 and ttyUSB1 created - something is wrong
>>> Try reading from USB0
root@chumby-falconwing:~# cat /dev/ttyUSB0
[ 193.350000] ftdi_sio ttyUSB0: ftdi_set_termios FAILED to set databits/stopbits/parity
[ 193.360000] ftdi_sio ttyUSB0: ftdi_set_termios urb failed to set baudrate
[ 193.370000] ftdi_sio ttyUSB0: urb failed to clear flow control
[ 193.380000] Unable to handle kernel NULL pointer dereference at virtual address 00000030
[ 193.390000] pgd = c3dd4000
[ 193.390000] [00000030] *pgd=43dcd031, *pte=00000000, *ppte=00000000
[ 193.400000] Internal error: Oops: 817 [#1] PREEMPT
[ 193.400000] Modules linked in: ftdi_sio usbserial ipv6 sd_mod usb_storage scsi_mod mousedev
[ 193.400000] CPU: 0 Not tainted (2.6.28-chumby #1)
[ 193.400000] PC is at ftdi_open+0x1dc/0x24c [ftdi_sio]
[ 193.400000] LR is at update_mctrl+0xf8/0x214 [ftdi_sio]
[ 193.400000] pc : [<bf097da4>] lr : [<bf097228>] psr: 60000013
[ 193.400000] sp : c3ddbd88 ip : 00000002 fp : c3ddbdc4
[ 193.400000] r10: c394ec80 r9 : 00000001 r8 : c396b804
[ 193.400000] r7 : c28acc00 r6 : c28ac000 r5 : c289ad00 r4 : c396b800
[ 193.400000] r3 : 00000000 r2 : c0000480 r1 : 00000000 r0 : ffffffe0
[ 193.400000] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
[ 193.400000] Control: 0005317f Table: 43dd4000 DAC: 00000015
[ 193.400000] Process cat (pid: 429, stack limit = 0xc3dda268)
[ 193.400000] Stack: (0xc3ddbd88 to 0xc3ddc000)
[ 193.400000] bd80: 00000000 00000001 c3ddbda4 00000000 00001388 c3ddbda8
[ 193.400000] bda0: c020cb60 c01e9740 c396b800 c39c7f60 c28acc00 c396b83c c3ddbdf4 c3ddbdc8
[ 193.400000] bdc0: bf08b364 bf097bd8 bf08b218 c3fef600 c394ec80 0bc00000 00000000 c3dda000
[ 193.400000] bde0: 00000000 c28acc00 c3ddbe34 c3ddbdf8 c0206e18 bf08b228 00000000 c3debd20
[ 193.400000] be00: 000000bc 00000000 00000000 c3debd20 c394ec80 c3fef608 00000000 00000000
[ 193.400000] be20: c3dda000 00000000 c3ddbe64 c3ddbe38 c009e078 c0206b68 00000024 00000000
[ 193.400000] be40: c3ddbe5c c3fd5b80 c34f2480 c394ec80 c3debd20 c009de80 c3ddbe8c c3ddbe68
[ 193.400000] be60: c0098b24 c009de90 c394ec80 00000000 00000000 00020000 00000000 40025000
[ 193.400000] be80: c3ddbeac c3ddbe90 c0099edc c0098994 00000000 00000000 00000000 00020001
[ 193.400000] bea0: c3ddbf64 c3ddbeb0 c00a60dc c0099eb0 00020001 c398c898 c3ddbfb0 400dd000
[ 193.400000] bec0: 00000000 c3bdec34 c3dd4000 00000000 00020000 00000024 c3fd5b80 c34f2480
[ 193.400000] bee0: 000000b7 00000000 00000000 00000101 00000001 00000000 c3dd5000 000000dd
[ 193.400000] bf00: 00000200 00000000 4f97d20d c398f800 c398f800 c3ddbfb0 00000000 00020001
[ 193.400000] bf20: 00000000 c394ec80 00020000 00000003 c3ddbf64 c3ddbf40 c00afd58 00000003
[ 193.400000] bf40: c399e000 ffffff9c 00020000 00000000 c3dda000 40025000 c3ddbf94 c3ddbf68
[ 193.400000] bf60: c0099f50 c00a5d84 00000002 40025000 c3ddbf9c bef87f05 00008000 0000005e
[ 193.400000] bf80: 00000005 c0025fa4 c3ddbfa4 c3ddbf98 c009a004 c0099f04 00000000 c3ddbfa8
[ 193.400000] bfa0: c0025e20 c0099fec bef87f05 00008000 bef87f05 00020000 00000000 00000000
[ 193.400000] bfc0: bef87f05 00008000 0000005e 00000005 00019248 00000002 40025000 00000000
[ 193.400000] bfe0: 400dd730 bef87bb0 0000949c 400dd774 60000010 bef87f05 40578031 40578431
[ 193.400000] Backtrace:
[ 193.400000] [<bf097bc8>] (ftdi_open+0x0/0x24c [ftdi_sio]) from [<bf08b364>] (serial_open+0x14c/0x1b8 [usbserial])
[ 193.400000] r7:c396b83c r6:c28acc00 r5:c39c7f60 r4:c396b800
[ 193.400000] [<bf08b218>] (serial_open+0x0/0x1b8 [usbserial]) from [<c0206e18>] (tty_open+0x2c0/0x41c)
[ 193.400000] [<c0206b58>] (tty_open+0x0/0x41c) from [<c009e078>] (chrdev_open+0x1f8/0x220)
[ 193.400000] [<c009de80>] (chrdev_open+0x0/0x220) from [<c0098b24>] (__dentry_open+0x1a0/0x2bc)
[ 193.400000] r8:c009de80 r7:c3debd20 r6:c394ec80 r5:c34f2480 r4:c3fd5b80
[ 193.400000] [<c0098984>] (__dentry_open+0x0/0x2bc) from [<c0099edc>] (nameidata_to_filp+0x3c/0x54)
[ 193.400000] [<c0099ea0>] (nameidata_to_filp+0x0/0x54) from [<c00a60dc>] (do_filp_open+0x368/0x738)
[ 193.400000] r4:00020001
[ 193.400000] [<c00a5d74>] (do_filp_open+0x0/0x738) from [<c0099f50>] (do_sys_open+0x5c/0xe8)
[ 193.400000] [<c0099ef4>] (do_sys_open+0x0/0xe8) from [<c009a004>] (sys_open+0x28/0x2c)
[ 193.400000] r8:c0025fa4 r7:00000005 r6:0000005e r5:00008000 r4:bef87f05
[ 193.400000] [<c0099fdc>] (sys_open+0x0/0x2c) from [<c0025e20>] (ret_fast_syscall+0x0/0x2c)
[ 193.400000] Code: e1822403 e3822103 e5943070 e3822080 (e5832030)
[ 193.760000] ---[ end trace 2a70456d12a8a105 ]---
Segmentation fault
Like I said, my CHB kernel code isn't in a very clean state right now, so your mileage may vary. I hope it does.