nietzsche at lysator.liu.se nietzsche at lysator.liu.se
Wed Mar 2 15:28:30 UTC 2016

FWIW: I can see this bug on the latest TeliaSonera E3372 in MBIM-mode as


> Im pretty sure their NCM devices are able to send supported NTB formats.
> At least the Huawei driver indicates this.
> They just change  pointers to the structs for 16/32 bit mode.
> //MDen 2 mar 2016 09:51 skrev Bjørn Mork <bjorn at mork.no>:
>> Bjørn Mork <bjorn at mork.no> writes:
>> > The Windows driver sends a "reset function" request after the "get NTB
>> > parameters" request.  The Linux driver doesn't do that.  Might make
>> a
>> > difference.  And it sends another "reset function" request just when
>> > you'd think the setup was complete, restarting it all.  Don't know
>> why
>> > it does that.  Makes no sense to me.  But we could try it just for
>> > completeness.
>> I had to reread the spec to see if there is any reasons there for us to
>> do this, but I still cannot see any.  Assuming the device is conforming
>> to spec that is, which it clearly isn't.  So we can add the reset to
>> replicate Windows behaviour in case some buggy firmware expects it, but
>> that is the only reason.
>> Rereading the NCM spec regarding device behaviour on "set interface" was
>> far more interesting. I can recommend Huawei to review the section
>> "7.2 Using Alternate Settings to Reset an NCM Function".  In short, the
>> device is supposed to reset all relevant settins to default when the
>> host selects altsetting 0.  And one of those defaults is:
>>   "reset the NTB format to NTB-16"
>> So there you have it.  The device should never operate in NTB-32 unless
>> the host/driver explicitly selected that mode.
>> But whatever.  If Windows selects NTB-32, then we might have to do the
>> same. It will complicate the driver - unnecessarily IMHO.  But I am
>> hoping that we can avoid configuring any vendor or devices specific
>> quirks for this, though.  Let's cross fingers that Huawei at least have
>> implemented a working "get NTB format" (required for devices supporting
>> NTB-32), so that we can automatically detect devices refusing to operate
>> in NTB-16 mode.
>> Bjørn
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