F12:: Huawei E220 - 3G modem

[linux.ninjas groupadmin]

Interesting article in you have a older E220 Huawei modem

http://www.jethrocarr.com/?cms=blog:20091207


HUAWEI E220 WITH FEDORA 12

However I discovered that my Huawei E220 3G Modem (branded as "Vodem"
here in NZ) was now failing to work - when trying to connect,
NetworkManager would start, the connection would run for a few seconds
and then suddenly disconnect. I would also receive a popup saying that
sr0 was unable to be mounted.

The 3G modem would then fail to appear in Network Manager and the
kernel log showed lots of weird USB errors.

The Huawei E220 is an interesting device, it has both a 3G modem and
also a USB "SCSI CDROM" drive which contains drivers for when plugged
into a Windows computer. However this dual-device operation has
historically caused no end of different problems across various Linux
releases.

In Fedora 12, it seems that the "cdrom" (usbstorage) and 3G Modem
(usbserial) drivers fight each other - first the usbserial driver
works as expected, connects to the network and Network Manager runs
OK. However a second later the "cdrom" tries to get mounted and
glitches, breaking both drivers and dropping the connection.



SOLUTION

You can't work around it by trying some of the past workarounds with
older Linux releases such as removing the usbstorage module or apply
custom vendor & product options to the usbserial module, either
workaround will break the newer version of NetworkManager/
ModemManager.

Fortunately the fix is relatively simple - we just need to tell the
system to ignore the "cdrom" - which we can do by using Udev. Simply
create the file /etc/udev/rules.d/20-custom-huawei.rules with the
contents of:

# work around dodgy Huawei modem
SUBSYSTEMS=="scsi" ATTRS{vendor}=="HUAWEI", OPTIONS+="ignore_device"


Then re-plug the Huawei and the system will detect both the 3G Modem
and the "cdrom", however the ignore_device option will cause udev to
avoid trying to mount the CDROM and therefore permits the 3G modem to
work uninterrupted. :-)