[Ftdi-usb-sio-devel] FT4232H semi-randomly fails to read EEPROM on cold reboot

[Joakim L. <joa...@to...>]

Hi,

I have a very odd problem with FT4242H devices, which I hope someone 
recognizes.

The FT4242H uses an external EEPROM for things like vendor/product 
strings and serial number. Without the external EEPROM the 
vendor/product strings reverts to defaults and there is no support for a 
serial number (which is the thing I'm really interested in). Typically I 
keep 4 separate devices conneced (so a total of 16 ports). On a cold 
reboot only about half of the FT4242H devices will read the EEPROM 
contents. The rest of them will just report defaults when examined with 
udevadm info. When one of the devices, which failed to report a serial 
number, is unplugged and plugged back in it will always succeed in 
reading the EEPROM contents, and will report the stored serial number. 
I've seen this issue turn up in both kernel 2.6.32.26 and 2.6.40.4.

The problem does not seem to be tied to particular devices. For example, 
if I swap a working and a non-working board the problem usually does not 
move with the board. If anything, specific USB ports seems to work 
better than others, but that's not the full explanation either. So far 
I've not been able to spot any significant difference between a 
successful and failed read in dmesg or messages.

Is there anyone here who is familiar with this type of problem?


Best regards,

-- 
Joakim Linde
Tangiamo AB (formerly TouchTable AB)