E3276: Failed to find primary AT port

Bjørn Mork bjorn at mork.no
Mon Jun 16 08:42:07 PDT 2014

"Georg Lippitsch" <georg.lippitsch at gmx.at> writes:
> Am 12.06.2014, 11:29 Uhr, schrieb Bjørn Mork <bjorn at mork.no>:
>>> It's probably better to try recent kernel git, I will report when I
>>> have done this.
> Ok, I now tried with the 3.15 Kernel from here:
> http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.15-utopic/
> The Problem is the same: Modem works well when connected for the first
> time, but fails when re-pluged. No /dev/cdc-wdm0 anymore.
> I also noticed that after unplugging the modem and unloading
> "huawei_cdc_ncm", the "cdc_wdm" module is still "Used by 1", and it's
> not possible to unload it.

This sounds like we might crash something on disconnect.  Did you see an
Oops or similar from this?  I don't have any modem supported by this
driver myself, so I cannot easily recreate the problem.  So a stack
trace from the crash would help a lot.

> This is not the case with my Huawei E398: After unpluging the modem, I
> can smoothly unload "cdc_wdm".

Yes, that's the way it is supposed ot be

> I also followed your discussion about buffer sizes in cdc_wdm. Do you
> think this could be related to the problem?

Nope, that's unlikely.

> I'd also be happy to look in the source codes, if you could give me a
> hint where to start ;-)

That would be great! Debugging such problems is a great way to start
hacking on Linux.

I assume the problem is somewhere in the cleanup/disconnect code in
huawei_cdc_ncm.c.  Look at the unbind function there, and compare it to
the similar ones in qmi_wwan.c and cdc_mbim.c (which both fine work

Make sure to CC Enrico if you find anything interesting.  He's the one
behind this driver.


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