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Old 01-30-2013, 08:31 AM   #1
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Question [ubuntu] recompile sierra 3G modem driver sierra.ko with custom wireless-regdb

Hi all!

in my ubuntu laptop I have both a WiFi-card and a sierra 3G (UMTS) modem built in.

Because the wifi card is imported and I need to use certain channels not allowed in the card's country of origin to connect to the local university network I installed a custom, self-signed wireless-regdb.

This works great for the WiFi card, but unfortunately whenever I load the custom wireless-regdb, my sierra 3G modem card goes offline and is not detected any more by network manager.

My suspicion is that the UMTS-Modem's driver does not recognize the custom regdb's signature as valid and therefore shuts down. (The behaviour is much the same with stock crda for wifi cards).

With crda there is an option to include custom public keys in the source code and recompile, so the system will from then on recognize frequency databases signed with this custom key as valid and use them.

Does anyone know of a similare procedure for the sierra 3G modem driver kernel module (sierra.ko)?

crda is listed as a dependency for that module, so I am confident to be on the right track, but unfortunately I have until now found zero documentation on the subject.

Can anyone help please?

Old 01-30-2013, 09:43 AM   #2
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Registered: Jul 2012
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Update: never mind.

My UMTS modem is reliably detected using the stock CRDA, and never detected on boot using my custom CRDA, which led me to suspect some kind of regulatory intervention.

It turns out though the card not being detected is probably a bug, not a feature.

I can get the card online while using the custom regdb and CRDA by just repeatedly setting and resetting the hardware radio kill switch on my laptop. It never works the first time, but there's about a 30% success rate when switching wireless radio off and back on 5 times.

It seems there is some kind of race condition in network manager, which prevents it from properly loading the modem driver, and my custom regdb (which is considerably larger than the stock version) seems to trigger that bug.


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