cab4b54ad1
Most older Qualcomm SoCs (e.g. MSM8916, MSM8974, ...) communicate with the integrated modem via shared memory (SMD channels). This is similar to QRTR on newer SoCs, but without the "network" layer. In fact, the older SoCs also have QRTR, but the modem QMI services are not exposed there. The mainline Linux kernel exposes SMD channels via the "remote processor messaging bus" (rpmsg). Through special IOCTL calls it is possible to create a char device for a rpmsg/SMD channel. We can then use these to send QMI/AT messages to the modem, much like the ordinary serial char devices when using a Qualcomm modem through USB. This commit introduces support for the new 'rpmsg' subsystem, which allows exporting QMI-capable and AT-capable ports. By default NO rpmsg port is flagged as candidate, it is assumed that the plugin adding support for the rpmsg subsystem will add specific rules to do so (e.g. so that non-modem ports are explicitly not flagged as candidate). All rpmsg ports will be probed for AT or QMI capabilities, unless explicit port type hints (e.g. ID_MM_PORT_TYPE_QMI or ID_MM_PORT_TYPE_AT_PRIMARY) are set. These changes are highly based on the initial integration work done by Stephan Gerhold <stephan@gerhold.net> in postmarketOS, see: https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/363
ModemManager. ModemManager provides a unified high level API for communicating with mobile broadband modems, regardless of the protocol used to communicate with the actual device (Generic AT, vendor-specific AT, QCDM, QMI, MBIM...). Using. ModemManager is a system daemon and is not meant to be used directly from the command line. However, since it provides a DBus API, it is possible to use 'dbus-send' commands or the new 'mmcli' command line interface to control it from the terminal. The devices are queried from udev and automatically updated based on hardware events, although a manual re-scan can also be requested to look for RS232 modems. Implementation. ModemManager is a DBus system bus activated service (meaning it's started automatically when a request arrives). It is written in C, using glib and gio. Several GInterfaces specify different features that the modems support, including the generic MMIfaceModem3gpp and MMIfaceModemCdma which provide basic operations for 3GPP (GSM, UMTS, LTE) or CDMA (CDMA1x, EV-DO) modems. If a given feature is not available in the modem, the specific interface will not be exported in DBus. Plugins. Plugins are loaded on startup, and must implement the MMPlugin interface. It consists of a couple of methods which tell the daemon whether the plugin supports a port and to create custom MMBroadbandModem implementations. It most likely makes sense to derive custom modem implementations from one of the generic classes and just add (or override) operations which are not standard. There are multiple fully working plugins in the plugins/ directory that can be used as an example for writing new plugins. Writing new plugins is highly encouraged! The plugin API is open for changes, so if you're writing a plugin and need to add or change some public method, feel free to suggest it! License. The ModemManager and mmcli binaries are both GPLv2+. The libmm-glib library is LGPLv2+.