HP lt4120 failing to make single-stack connections on LTE using MM

[Tore Anderson]

Hi,

I have an 'HP lt4120 Snapdragon X5 LTE' WWAN module running firmware
revision 'T77W595.F0.0.0.6.6.GC.029  1  [Jul 06 2016 23:00:00' (latest
available on HP's web site).

It tends to frequently get to a state where MM fails to establish single-
stack connections while in LTE coverage. I'm pretty sure it's not a
network or subscription problem as the problem is there in different
PLMNs and SIM cards from different operators, and it works fine using
other UEs like Android and Jolla phones. I've set up the 3GPP profile
like so:

$ sudo qmicli -p -d /dev/cdc-wdm0 --wds-get-profile-list=3gpp
Profile list retrieved:
        [1] 3gpp - profile1
                APN: 'telenor.smart'
                PDP type: 'ipv6'
                Auth: 'none'

Using qmicli it seems to connect without problems:

$ sudo qmicli -p -d /dev/cdc-wdm0 --wds-start-network=3gpp-profile=1
[/dev/cdc-wdm0] Network started
        Packet data handle: '68385664'

But MM fails (and so does NM):

$ sudo /usr/bin/mmcli -m 0 --simple-connect=apn=telenor.smart,ip-type=ipv6
error: couldn't connect the modem: 'Timeout was reached'

This results in the following being logged:

<info>  Simple connect started...
<info>  Simple connect state (4/8): Wait to get fully enabled
<info>  Simple connect state (5/8): Register
<info>  Simple connect state (6/8): Bearer
<info>  Simple connect state (7/8): Connect
<info>  Modem /org/freedesktop/ModemManager1/Modem/0: state changed (registered -> connecting)
<info>  Modem /org/freedesktop/ModemManager1/Modem/0: state changed (connecting -> registered)
[/dev/cdc-wdm0] No transaction matched in received message
[/dev/cdc-wdm0] Received unexpected message (translated)...
>>>>>> Header:
>>>>>>   length      = 76
>>>>>>   type        = command-done (0x80000003)
>>>>>>   transaction = 31
>>>>>> Fragment header:
>>>>>>   total   = 1
>>>>>>   current = 0
>>>>>> Contents:
>>>>>>   status error = 'Failure' (0x00000002)
>>>>>>   service      = 'basic-connect' (a289cc33-bcbb-8b4f-b6b0-133ec2aae6df)
>>>>>>   cid          = 'packet-service' (0x0000000a)

It only happens in LTE coverage, UMTS and GSM has no issues at all. Also
it only seems to happen with the single-stack IP types (both IPv4- and
IPv6-only), never with dual-stack.

Anyone seen something like this before and have any suggestion on how to
avoid/prevent it?

If I power down my laptop completely and bring it back up, that might
might shake it loose for a while, but my test scripts that iterates
through all PLMNs and all RATs and tries to connect in each using all
three IP types will usually get it back in the stuck state again.

Is there a way to fully power cycle the WWAN module without
powercycling the entire laptop, by the way?

Tore