I have a embedded computer running 11.3 (stuck with that version) that has USB device issues.

In reality, it has two USB devices attached, both FTDI FT232 USB to Serial Uart driven hardware. Both usually are at /dev/ttyUSB0 and 1 when everything goes right. The latest FTDI driver is already in the kernel.

Randomly however, when it boots one or both will be missing in dev.

If we only leave one physically attached before booting, sometimes it comes up ok, the other times there's no listing in /dev/ or lsusb. But when we do run lsusb once and watch the system log, suddenly the device is found and 'attached'. Then it works fine.

I've repeated this with another test USB device (and old cell phone that gets installed as a ceullar modem) and the same thing can happen. It will randomlyy be missing from lsusb listing till lsusb is run once. IE, run it once, no listing, run it again, then it shows up and the system log saya it was just attached.

If we leave both, sometimes one device (Call this one A) is ready to go, but device B is missing. If we unplug B, A dissapears from /dev/ and the system log says A was unpluged. The when we reattach B, both show up in /dev/ and the system log reports two USB devices were attached. running lsusb doesn't fix one or both missing when they are both physically attached.

This is an embedded system and we need both to be discovered at boot 100% of the time. Any ideas what might be going on?

I do mean 11.3, sorry about that.

I think that comparing dmesg between when it works right and when it doesn't work right might help to give us a clue what is happening.

I'll try to capture the dmesg next time I'm near the system, but from what I remember it looked normal, nothing related to USB when the system boots with no devices logically found, till you run lsusb when the tail is updateds with messages about a new USB device attached.

In the meantime,

I think we have narrowed this problem down to a linux<->chipset driver issue. ANYTHING usb will randomly not be present at boot. Keyboards, mice, etc. Sometimes running lsusb 'discovers' the devices, sometimes not.

Disabling Legacy USB support in the bios seems to make the problem less prevalent, (1 out of 8 boots as opposed to 3 out of 5) but doesn't fix it completely.

The computer is Atom z530 processor based with the US15W chipset.

We are trying to sneak in a kernel update, but it would help if we found knowledge of this bug first for justification.

Some distros make you want a long time on boot. The statement is something like waiting for usb devices to settle. I think there is a way to add in some wait time on boot at that point to try to fix that.

But, I do know that many of those usb to serial devices stink and they could be causing this.