The libqmi and libmbim libraries are every day getting more popular to control your QMI or MBIM based devices. One of the things I’ve noticed, though, is that lots of users are writing applications in e.g. Python but then running qmicli or mbimcli commands, and parsing the outputs. This approach may work, but there is absolutely no guarantee that the format of the output printed by the command line programs will be kept stable across new releases. And also, the way these operations are performed may be suboptimal (e.g. allocating QMI clients for each operation, instead of reusing them).
Since the new stable libqmi 1.26 and libmbim 1.24 releases, these libraries integrate GObject Introspection support for all their types, and that provides a much better integration within Python applications (or really, any other language supported by GObject Introspection).
The only drawback of using the libraries in this way, if you’re already using and parsing command line interface commands, is that you would need to go deep into how the protocol works in order to use them.
For example, in order to run a DMS Get Capabilities operation, you would need to create a Qmi.Device first, open it, then allocate a Qmi.Client for the DMS service, then run the Qmi.Client.get_capabilities() operation, receive and process the response with Qmi.Client.get_capabilities_finish(), and parse the result with the per-TLV reader method, e.g. output.get_info() to process the Info TLV. Once the client is no longer needed, it would need to be explicitly released before exiting. A full example doing just this is provided in the libqmi sources.
In the case of MBIM operations, there is no need for the extra step of allocating a per-service client, but instead, the user should be more aware of the actual types of messages being transferred, in order to use the correct parsing operations. For example, in order to query device capabilities you would need to create a Mbim.Device first, open it, create a message to query the device capabilities, send the message, receive and process the response, check whether an error is reported, and if it isn’t, fully parse it. A full example doing just this is provided in the libmbim sources.
Of course, all these low level operations can also be done through the qmi-proxy or mbim-proxy, so that ModemManager or other programs can be running at the same time, all sharing access to the same QMI or MBIM ports.
P.S.: not a true Python or GObject Introspection expert here, so please report any issue found or improvements that could be done 😀
And special thanks to Vladimir Podshivalov who is the one that started the hard work of setting everything up in libqmi. Thank you!
The Dell Wireless 5821e module is a Qualcomm SDX20 based LTE Cat16 device. This modem can work in either MBIM mode or QMI mode, and provides different USB layouts for each of the modes. In Linux kernel based and Windows based systems, the MBIM mode is the default one, because it provides easy integration with the OS (e.g. no additional drivers or connection managers required in Windows) and also provides all the features that QMI provides through QMI over MBIM operations.
The firmware update process of this DW5821e module is integrated in your GNU/Linux distribution, since ModemManager 1.10.0 and fwupd 1.2.6. There is no official firmware released in the LVFS (yet) but the setup is completely ready to be used, just waiting for Dell to publish an initial official firmware release.
The firmware update integration between ModemManager and fwupd involves different steps, which I’ll try to describe here so that it’s clear how to add support for more devices in the future.
1) ModemManager reports expected update methods, firmware version and device IDs
The Firmware interface in the modem object exposed in DBus contains, since MM 1.10, a new UpdateSettings property that provides a bitmask specifying which is the expected firmware update method (or methods) required for a given module, plus a dictionary of key-value entries specifying settings applicable to each of the update methods.
In the case of the DW5821e, two update methods are reported in the bitmask: “fastboot” and “qmi-pdc“, because both are required to have a complete firmware upgrade procedure. “fastboot” would be used to perform the system upgrade by using an OTA update file, and “qmi-pdc” would be used to install the per-carrier configuration files after the system upgrade has been done.
The list of settings provided in the dictionary contain the two mandatory fields required for all devices that support at least one firmware update method: “device-ids” and “version”. These two fields are designed so that fwupd can fully rely on them during its operation:
- The “device-ids” field will include a list of strings providing the device IDs associated to the device, sorted from the most specific to the least specific. These device IDs are the ones that fwupd will use to build the GUIDs required to match a given device to a given firmware package. The DW5821e will expose four different device IDs:
- “USB\VID_413C“: specifying this is a Dell-branded device.
- “USB\VID_413C&PID_81D7“: specifying this is a DW5821e module.
- “USB\VID_413C&PID_81D7&REV_0318“: specifying this is hardware revision 0x318 of the DW5821e module.
- “USB\VID_413C&PID_81D7&REV_0318&CARRIER_VODAFONE“: specifying this is hardware revision 0x318 of the DW5821e module running with a Vodafone-specific carrier configuration.
- The “version” field will include the firmware version string of the module, using the same format as used in the firmware package files used by fwupd. This requirement is obviously very important, because if the format used is different, the simple version string comparison used by fwupd (literally ASCII string comparison) would not work correctly. It is also worth noting that if the carrier configuration is also versioned, the version string should contain not only the version of the system, but also the version of the carrier configuration. The DW5821e will expose a firmware version including both, e.g. “T77W968.F184.108.40.206.1.VF.001” (system version being F220.127.116.11.1 and carrier config version being “VF.001”)
- In addition to the mandatory fields, the dictionary exposed by the DW5821e will also contain a “fastboot-at” field specifying which AT command can be used to switch the module into fastboot download mode.
2) fwupd matches GUIDs and checks available firmware versions
Once fwupd detects a modem in ModemManager that is able to expose the correct UpdateSettings property in the Firmware interface, it will add the device as a known device that may be updated in its own records. The device exposed by fwupd will contain the GUIDs built from the “device-ids” list of strings exposed by ModemManager. E.g. for the “USB\VID_413C&PID_81D7&REV_0318&CARRIER_VODAFONE” device ID, fwupd will use GUID “b595e24b-bebb-531b-abeb-620fa2b44045”.
fwupd will then be able to look for firmware packages (CAB files) available in the LVFS that are associated to any of the GUIDs exposed for the DW5821e.
The CAB files packaged for the LVFS will contain one single firmware OTA file plus one carrier MCFG file for each supported carrier in the give firmware version. The CAB files will also contain one “metainfo.xml” file for each of the supported carriers in the released package, so that per-carrier firmware upgrade paths are available: only firmware updates for the currently used carrier should be considered. E.g. we don’t want users running with the Vodafone carrier config to get notified of upgrades to newer firmware versions that aren’t certified for the Vodafone carrier.
Each of the CAB files with multiple “metainfo.xml” files will therefore be associated to multiple GUID/version pairs. E.g. the same CAB file will be valid for the following GUIDs (using Device ID instead of GUID for a clearer explanation, but really the match is per GUID not per Device ID):
- Device ID “USB\VID_413C&PID_81D7&REV_0318&CARRIER_VODAFONE” providing version “T77W968.F18.104.22.168.2.VF.002”
- Device ID “USB\VID_413C&PID_81D7&REV_0318&CARRIER_TELEFONICA” providing version “T77W968.F22.214.171.124.2.TF.003”
- Device ID “USB\VID_413C&PID_81D7&REV_0318&CARRIER_VERIZON” providing version “T77W968.F126.96.36.199.2.VZ.004”
- … and so on.
Following our example, fwupd will detect our device exposing device ID “USB\VID_413C&PID_81D7&REV_0318&CARRIER_VODAFONE” and version “T77W968.F188.8.131.52.1.VF.001” in ModemManager and will be able to find a CAB file for the same device ID providing a newer version “T77W968.F184.108.40.206.2.VF.002” in the LVFS. The firmware update is possible!
3) fwupd requests device inhibition from ModemManager
In order to perform the firmware upgrade, fwupd requires full control of the modem. Therefore, when the firmware upgrade process starts, fwupd will use the new InhibitDevice(TRUE) method in the Manager DBus interface of ModemManager to request that a specific modem with a specific uid should be inhibited. Once the device is inhibited in ModemManager, it will be disabled and removed from the list of modems in DBus, and no longer used until the inhibition is removed.
The inhibition may be removed by calling InhibitDevice(FALSE) explicitly once the firmware upgrade is finished, and will also be automatically removed if the program that requested the inhibition disappears from the bus.
4) fwupd downloads CAB file from LVFS and performs firmware update
Once the modem is inhibited in ModemManager, fwupd can right away start the firmware update process. In the case of the DW5821e, the firmware update requires two different methods and two different upgrade cycles.
The first step would be to reboot the module into fastboot download mode using the AT command specified by ModemManager in the “at-fastboot” entry of the “UpdateSettings” property dictionary. After running the AT command, the module will reset itself and reboot with a completely different USB layout (and different vid:pid) that fwupd can detect as being the same device as before but in a different working mode. Once the device is in fastboot mode, fwupd will download and install the OTA file using the fastboot protocol, as defined in the “flashfile.xml” file provided in the CAB file:
<parts interface="AP"> <part operation="flash" partition="ota" filename="T77W968.F220.127.116.11.2.AP.123_ota.bin" MD5="f1adb38b5b0f489c327d71bfb9fdcd12"/> </parts>
Once the OTA file is completely downloaded and installed, fwupd will trigger a reset of the module also using the fastboot protocol, and the device will boot from scratch on the newly installed firmware version. During this initial boot, the module will report itself running in a “default” configuration not associated to any carrier, because the OTA file update process involves fully removing all installed carrier-specific MCFG files.
The second upgrade cycle performed by fwupd once the modem is detected again involves downloading all carrier-specific MCFG files one by one into the module using the QMI PDC protocol. Once all are downloaded, fwupd will activate the specific carrier configuration that was previously active before the download was started. E.g. if the module was running with the Vodafone-specific carrier configuration before the upgrade, fwupd will select the Vodafone-specific carrier configuration after the upgrade. The module would be reseted one last time using the QMI DMS protocol as a last step of the upgrade procedure.
5) fwupd removes device inhibition from ModemManager
The upgrade logic will finish by removing the device inhibition from ModemManager using InhibitDevice(FALSE) explicitly. At that point, ModemManager would re-detect and re-probe the modem from scratch, which should already be running in the newly installed firmware and with the newly selected carrier configuration.
I’ve been lately working on integrating ModemManager in OpenWRT, in order to provide a unique and consolidated way to configure and manage mobile broadband modems (2G, 3G, 4G, Iridium…), all working with
OpenWRT already has some support for a lot of the devices that ModemManager is able to manage (e.g. through the
wwan packages), but unlike the current solutions, ModemManager doesn’t require protocol-specific configurations or setups for the different devices; i.e. the configuration for a modem running in MBIM mode may be the same one as the configuration for a modem requiring AT commands and a PPP session.
Currently the OpenWRT package prepared is based on ModemManager git master, and therefore it supports: QMI modems (including the new MC74XX series which are raw-ip only and don’t support DMS UIM operations), MBIM modems, devices requiring QMI over MBIM operations (e.g. FCC auth), and of course generic AT+PPP based modems, Cinterion, Huawei (both AT+PPP and AT+NDISDUP), Icera, Haier, Linktop, Longcheer, Ericsson MBM, Motorola, Nokia, Novatel, Option (AT+PPP and HSO), Pantech, Samsung, Sierra Wireless (AT+PPP and DirectIP), Simtech, Telit, u-blox, Wavecom, ZTE… and even Iridium and Thuraya satellite modems. All with the same configuration.
Along with ModemManager itself, the OpenWRT feed also contains libqmi and libmbim, which provide the
mbimcli, and soon the
qmi-firmware-update utilities. Note that you can also use these command line tools, even if ModemManager is running, via the qmi-proxy and mbim-proxy setups (i.e. just adding
-p to the
This is not the first time I’ve tried to do this; but this time I believe it is a much more complete setup and likely ready for others to play with it. You can jump to the modemmanager-openwrt bitbucket repository and follow the instructions to include it in your OpenWRT builds:
The following sections try to get into a bit more detail of which were the changes required to make all this work.
And of course, thanks to VeloCloud for sponsoring the development of the latest ModemManager features that made this integration possible 🙂
udev vs hotplug
One of the latest biggest features merged in ModemManager was the possibility to run without
udev support; i.e. without automatically monitoring the device addition and removals happening in the system.
Instead of using
mmcli command line tool ended up with a new
--report-kernel-event that can be used to report the device addition and removals manually, e.g.:
$ mmcli --report-kernel-event="action=add,subsystem=tty,name=ttyUSB0" $ mmcli --report-kernel-event="action=add,subsystem=net,name=wwan0"
With the integration in the hotplug scripts, ModemManager will automatically detect and probe the different ports exposed by the broadband modem devices.
ModemManager relies on udev rules for different things:
- Blacklisting devices: E.g. we don’t want ModemManager to claim and probe the TTYs exposed by Arduinos or braille displays. The package includes a USB vid:pid based blacklist of devices that expose TTY ports and are not modems to be managed by ModemManager.
- Blacklisting ports: There are cases where we don’t want the automatic logic selection to grab and use some specific modem ports, so the package also provides a much shorter list of ports blacklisted from actual modem devices. E.g. the QMI implementation in some ZTE devices is so poor that we decided to completely skip it and fallback to AT+PPP.
- Greylisting USB serial adapters: The TTY ports exposed by USB serial adapters aren’t probed automatically, as we don’t know what’s connected in the serial side. If we want to have a serial modem, though, the
mmcli --scan-modemsoperation may be executed, which will include the probing of these greylisted devices.
- Specifying port type hints: Some devices expose multiple AT ports, but with different purposes. E.g. a modem may expose a port for AT control and another port for the actual PPP session, and choosing the wrong one will not work. ModemManager includes a list of port type hints so that the automatic selection of which port is for what purpose is done transparently.
As we’re not using udev when running in OpenWRT, ModemManager includes now a custom generic udev rules parser that uses sysfs properties to process and apply the rules.
procd based startup
The ModemManager daemon is setup to be started and controlled via
procd. The init script controlling the startup will also take care of scheduling the re-play of the hotplug events that had earlier triggered
--report-kernel-event actions (they’re cached in
/tmp); e.g. to cope with events coming before the daemon started or to handle daemon restarts gracefully.
Well, no, I didn’t port ModemManager to use
ubus 🙂 If you want to run ModemManager under OpenWRT you’ll also need to have the
DBus daemon running.
netifd protocol handler
When using ModemManager, the user shouldn’t need to know the peculiarities of the modem being used: all modems and protocols (QMI, MBIM, Generic AT, vendor-specific AT…) are all managed via the same single DBus interfaces. All the modem control commands are internal to ModemManager, and the only additional considerations needed are related to how to setup the network interface once the modem is connected, e.g.:
- PPP: some modems require a PPP session over a serial port.
- Static: some modems require static IP configuration on a network interface.
- DHCP: some modems require dynamic IP configuration on a network interface.
The OpenWRT package for ModemManager includes a custom protocol handler that enables the modemmanager protocol to be used when configuring network interfaces. This new protocol handler takes care of configuring and bringing up the interfaces as required when the modem gets into connected state.
The following snippet shows an example interface configuration to set in
config interface 'broadband' option device '/sys/devices/platform/soc/20980000.usb/usb1/1-1/1-1.2/1-1.2.1' option proto 'modemmanager' option apn 'ac.vodafone.es' option username 'vodafone' option password 'vodafone' option pincode '7423' option lowpower '1'
The settings currently supported are the following ones:
- device: The full sysfs path of the broadband modem device needs to be configured. Relying on the interface names exposed by the kernel is never a good idea, as these may change e.g. across reboots or when more than one modem device is available in the system.
- proto: As said earlier, the new modemmanager protocol needs to be configured.
- apn: If the connection requires an APN, the APN to use.
- username: If the access point requires authentication, the username to use.
- password: If the access point requires authentication, the password to use.
- pincode: If the SIM card requires a PIN, the code to use to unlock it.
- lowpower: If enabled, this setting will request the modem to go into low-power state (i.e. IMSI detach and RF off) when the interface is disconnected.
As you can see, the configuration can be used for any kind of modem device, regardless of what control protocol it uses, which interfaces are exposed, or how the connection is established. The settings are currently only IPv4 only, but adding IPv6 support shouldn’t be a big issue, patches welcome 🙂
SMS, USSD, GPS…
The main purpose of using a mobile broadband modem is of course the connectivity itself, but it also may provide many more features. ModemManager provides specific interfaces and
mmcli actions for the secondary features which are also available in the OpenWRT integration, including:
- SMS messaging (both 3GPP and 3GPP2).
- Location information (3GPP LAC/CID, CDMA Base station, GPS…).
- Time information (as reported by the operator).
- 3GPP USSD operations (e.g. to query prepaid balance to the operator).
- Extended signal quality information (RSSI, Ec/Io, LTE RSRQ and RSRP…).
- OMA device management operations (e.g. to activate CDMA devices).
- Voice call control.
Worth noting that not all these features are available for all modem types (e.g. SMS messaging is available for most devices, but OMA DM is only supported in QMI based modems).
You can now have your 2G/3G/4G mobile broadband modems managed with ModemManager and netifd in your OpenWRT based system.