Forum Linux.debian/ubuntu Modem 4G KO sous Linux

TL;DR; J'ai un laptop Dell E5450 sur lequel je ne parviens pas à faire fonctionner le modem 4G embarqué. Sauriez-vous m'aider ?

Version longue

J'ai un ordinateur portable (aka laptop) Dell Latitude E5450 sur lequel se trouve un modem 4G Dell Wireless 5809e Gobi™ 4G LT. À priori, il s'agit d'un Sierra Wireless AirPrime EM7305 à base d'un Qualcomm MDM 9215 et "rebrandé" par Dell. Sur ce laptop tournent en double boot un Ubuntu Gnome 16.10 et un Windows 10. Je ne parviens pas à le faire fonctionner sous Linux alors que j'ai pu vérifier qu'il fonctionne "out of the box" sous Windows 10.

Voici les pages que j'ai pu consulter sur le sujet :

1. Stuff for Linux on a Dell Latitude E5*50
2. Dell Wireless 5809e support in openSUSE 13.2
3. Dell Wireless 5809e support in Linux – a followup la suite du précédent
4. Changing Dell Wireless 5809e / Sierra Wireless EM7305 USB composition (MBIM, QMI, AT interface, NMEA). La mise à jour des 2 précédents
5. Dell-branded Sierra Wireless 3G/4G modem not online?
6. novatel: improve probing for Dell branded modems

Les liens précédents concernent d'autres distros que la mienne, mais a priori d'autes que moi ont réussi à la faire fonctionner :

• Carte 4G sur Dell Latitude E7250
• Dell Wireless 5809e Gobi 4G LTE on Android x86

En me basant sur les liens donnés plus haut, je constate que

• J'ai bien les bons drivers qui se chargent :

$ usb-devices
[...]
T:  Bus=02 Lev=01 Prnt=01 Port=07 Cnt=02 Dev#=  3 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  2
P:  Vendor=413c ProdID=81b1 Rev=00.06
S:  Manufacturer=Sierra Wireless, Incorporated
S:  Product=Dell Wireless 5809e Gobi™ 4G LTE Mobile Broadband Card
C:  #Ifs= 4 Cfg#= 1 Atr=e0 MxPwr=500mA
I:  If#= 0 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=ff Prot=ff Driver=qcserial
I:  If#= 2 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=00 Driver=qcserial
I:  If#= 3 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=00 Driver=qcserial
I:  If#= 8 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=ff Prot=ff Driver=qmi_wwan
[...]

• extraits de la sortie de dmesg

[...]
[    3.574614] usb 2-8: New USB device found, idVendor=413c, idProduct=81b1
[    3.574616] usb 2-8: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[    3.574617] usb 2-8: Product: Dell Wireless 5809e Gobi™ 4G LTE Mobile Broadband Card
[    3.574618] usb 2-8: Manufacturer: Sierra Wireless, Incorporated
[...]
[    8.046612] usbcore: registered new interface driver qcserial
[    8.046625] usbserial: USB Serial support registered for Qualcomm USB modem
[    8.047174] qcserial 2-8:1.0: Qualcomm USB modem converter detected
[    8.047387] usb 2-8: Qualcomm USB modem converter now attached to ttyUSB0
[    8.060817] usbcore: registered new interface driver btusb
[...]
[    8.073493] usbcore: registered new interface driver cdc_wdm
[    8.078990] media: Linux media interface: v0.10
[    8.079101] qcserial 2-8:1.2: Qualcomm USB modem converter detected
[    8.079176] usb 2-8: Qualcomm USB modem converter now attached to ttyUSB1
[    8.079560] qcserial 2-8:1.3: Qualcomm USB modem converter detected
[    8.079619] usb 2-8: Qualcomm USB modem converter now attached to ttyUSB2
[...]
[    8.091125] qmi_wwan 2-8:1.8: cdc-wdm1: USB WDM device
[    8.091971] qmi_wwan 2-8:1.8 wwan0: register 'qmi_wwan' at usb-0000:00:14.0-8, WWAN/QMI device, 26:f1:c1:ed:4e:ed
[    8.091993] usbcore: registered new interface driver qmi_wwan
[...]
[    8.423289] qmi_wwan 2-8:1.8 wwp0s20u8i8: renamed from wwan0
[    8.450380] iwlwifi 0000:02:00.0 wlp2s0: renamed from wlan0
[...]
[    8.600909] audit: type=1400 audit(1489244459.886:2): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/sbin/dhclient" pid=921 comm="apparmor_parser"
[    8.600915] audit: type=1400 audit(1489244459.886:3): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/lib/NetworkManager/nm-dhcp-client.action" pid=921 comm="apparmor_parser"
[    8.600921] audit: type=1400 audit(1489244459.886:4): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/lib/NetworkManager/nm-dhcp-helper" pid=921 comm="apparmor_parser"
[    8.600925] audit: type=1400 audit(1489244459.886:5): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/lib/connman/scripts/dhclient-script" pid=921 comm="apparmor_parser"
[    8.601206] audit: type=1400 audit(1489244459.886:6): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/lib/snapd/snap-confine" pid=924 comm="apparmor_parser"
[    8.601213] audit: type=1400 audit(1489244459.886:7): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/lib/snapd/snap-confine//mount-namespace-capture-helper" pid=924 comm="apparmor_parser"
[    8.602731] audit: type=1400 audit(1489244459.886:8): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/sbin/cups-browsed" pid=926 comm="apparmor_parser"
[    8.604613] audit: type=1400 audit(1489244459.886:9): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/lib/cups/backend/cups-pdf" pid=927 comm="apparmor_parser"
[    8.604622] audit: type=1400 audit(1489244459.886:10): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/sbin/cupsd" pid=927 comm="apparmor_parser"
[    8.604626] audit: type=1400 audit(1489244459.886:11): apparmor="STATUS" operation="profile_load" profile="unconfined" name="/usr/sbin/cupsd//third_party" pid=927 comm="apparmor_parser"
[...]

• Je suis dans le bon mode de composition USB si j'en crois le script perl de Bjørn Mork référencé en point 4 plus haut

$ sudo ./swi_setusbcomp.pl 
Running in QMI mode (driver=qmi_wwan)
QMI msg '0x0021' returned status = 1
QMI support verified
supports 26 QMI subsystems:
  0x00 (1.5)    'QMI_CTL'   - Control service
  0x01 (1.36)   'QMI_WDS'   - Wireless data service
  0x02 (1.14)   'QMI_DMS'   - Device management service
  0x03 (1.25)   'QMI_NAS'   - Network access service
  0x04 (1.3)    'QMI_QOS'   - Quality of service, err, service 
  0x05 (1.10)   'QMI_WMS'   - Wireless messaging service
  0x06 (1.0)    'QMI_PDS'   - Position determination service
  0x07 (1.2)    'QMI_AUTH'  - Authentication service
  0x08 (1.2)    'QMI_AT'    - AT command processor service
  0x09 (2.1)    'QMI_VOICE' - Voice service
  0x0a (2.16)   'QMI_CAT2'  - Card application toolkit service (new)
  0x0b (1.25)   'QMI_UIM'   - UIM service
  0x0c (1.4)    'QMI_PBM'   - Phonebook service
  0x11 (1.0)    'QMI_SAR'   - Specific absorption rate service
  0x12 (1.0)    'QMI_IMSS'  - IMS settings service
  0x17 (1.0)    'QMI_TS'    - Thermal sensors service
  0x18 (1.0)    'QMI_TMD'   - Thermal mitigation device service
  0x1a (1.10)   'QMI_WDA'   - Wireless data administrative service
  0x1d (1.0)    'QMI_CSVT'  - Circuit switched videotelephony service
  0x1e (1.0)    'QMI_QCMAP' - Qualcomm mobile access point service
  0x1f (1.0)    'QMI_IMSP'  - IMS presence service
  0x20 (1.0)    'QMI_IMSVT' - IMS videotelephony service
  0x22 (1.0)    'QMI_COEX'  - Coexistence service
  0x29 (1.0)    'QMI_RFRPE' - RF radiated performance enhancement service
  0xe1 (1.0)    'QMI_RMS'   - Remote management service
  0xf0 (1.0)    'unknown'   - 
QMI msg '0x0022' returned status = 1
Got QMI DMS client ID '2'
QMI msg '0x555b' returned status = 1
Current USB composition: 14
USB compositions:
   0 - HIP  DM    NMEA  AT    MDM1  MDM2  MDM3  MS      NOT SUPPORTED
   1 - HIP  DM    NMEA  AT    MDM1  MS                  SUPPORTED
   2 - HIP  DM    NMEA  AT    NIC1  MS                  NOT SUPPORTED
   3 - HIP  DM    NMEA  AT    MDM1  NIC1  MS            NOT SUPPORTED
   4 - HIP  DM    NMEA  AT    NIC1  NIC2  NIC3  MS      NOT SUPPORTED
   5 - HIP  DM    NMEA  AT    ECM1  MS                  NOT SUPPORTED
   6 - DM   NMEA  AT    QMI                             SUPPORTED
   7 - DM   NMEA  AT    RMNET1 RMNET2 RMNET3            SUPPORTED
   8 - DM   NMEA  AT    MBIM                            SUPPORTED
   9 - MBIM                                             SUPPORTED
  10 - NMEA MBIM                                        SUPPORTED
  11 - DM   MBIM                                        SUPPORTED
  12 - DM   NMEA  MBIM                                  SUPPORTED
  13 - Config1: comp6    Config2: comp8                 NOT SUPPORTED
* 14 - Config1: comp6    Config2: comp9                 SUPPORTED
  15 - Config1: comp6    Config2: comp10                NOT SUPPORTED
  16 - Config1: comp6    Config2: comp11                NOT SUPPORTED
  17 - Config1: comp6    Config2: comp12                NOT SUPPORTED
  18 - Config1: comp7    Config2: comp8                 NOT SUPPORTED
  19 - Config1: comp7    Config2: comp9                 SUPPORTED
  20 - Config1: comp7    Config2: comp10                NOT SUPPORTED
  21 - Config1: comp7    Config2: comp11                NOT SUPPORTED
  22 - Config1: comp7    Config2: comp12                NOT SUPPORTED
QMI msg '0x0023' returned status = 1

• J'ai bien l'authentication FCC qui se fait si j'en crois le lien 5 donné plus haut. (Ma libqmi est en 1.12.6 et et ModemManager en 1.6 avec Ubuntu 16.10)

$ sudo qmicli -d /dev/cdc-wdm1 --dms-get-operating-mode
[/dev/cdc-wdm1] Operating mode retrieved:
    Mode: 'online'
    HW restricted: 'no'

J'ai beau mettre en œuvre la règle udev mentionnée dans les liens 1 ou 3, rien de change et impossible d'avoir accès à mon modem. Auriez-vous une idée de comment faire fonctionner ce foutu modem sous Linux ? Je suis à court d'idées.

J'aurais aussi bien posté un commentaire sur le blog Oxf8.org de Pieter mentionné plus haut, mais il ne les autorise pas.
Merci de votre aide.