likely kernel/driver problem with 3G USB stick

[greg@kroah.com (Greg KH)]

On Tue, Mar 01, 2011 at 04:41:56PM +0000, Simon Leung wrote:
> On 01/03/11 16:37, Greg KH wrote:
> > On Tue, Mar 01, 2011 at 04:10:43PM +0000, Simon Leung wrote:
> >> Hi all,
> >>
> >> I'm having a problem with my 3G USB stick (Huawei E220) .
> >>
> >> The kernel I'm using is version 2.6.21 customized for an ARM board. When
> >> I insert the USB stick into the system, normally 3 device show up:
> >> /dev/ttyUSB{0,1,2}. The problem I' having is that some time, only the
> >> first one shows up and I cannot connect to it. When this happens,
> >> normally a reboot will fix it.
> >>
> >> As I said, this sounds like a kernel/driver issue to me. Could somebody
> >> give me some pointers as how to prove/fix it?
> > As you are stuck with an obsolete kernel version, please get support
> > from the vendor of that kernel, it is very old and we can't do much, if
> > anything, about it :(
> >
> > Can you duplicate this problem on a modern kernel (like one released in
> > the past year?)
> >
> > thanks,
> >
> > greg k-h
> >
> 
> I know. I probably can (and probably will) upgrade the kernel and the 
> problem will probably go away. But I'd like to take the opportunity and 
> hopefully learn something. Even knowing which part of the kernel is  
> handling the usb serial device is fine.

The part is in drivers/usb/serial/ and it depends on the actual device
you are using, and the host controller you are using.

I place the odds on your host controller being the problem, for what
it's worth, especially on older ARM kernels like you are stuck with.

Best of luck,

greg k-h