Joachim Wiberg 600483c35b modem: route NMEA from cellular modems to gpsd
Cellular modems (Quectel EM05/EM06/EM12, Sierra EM7565, ...) expose
GPS data as NMEA on a dedicated USB serial interface.  Until now we
relied on ModemManager's --location-enable-gps-nmea, which makes MM
hold the NMEA port and parse the stream itself — useful for mmcli
but a dead end for the rest of the system.  The result was that
modem GPS was visible only via 'show modem' and could not act as an
NTP fallback time source on devices without dedicated GPS hardware.

This commit reroutes the NMEA stream into the existing
gpsd → chronyd pipeline so cellular modems behave just like any
other NMEA-over-USB GPS dongle.  No changes to gpsd, chronyd, or
the ietf-hardware:gps component — the user activates it the same
way as for a dedicated receiver, by adding a 'gps' hardware
component that references /dev/gpsN.

This is Phase 2 of the modem GPS / location integration plan
(.notes/modem-gps-plan.md).

udev (src/modemd/77-mm-modem-gps.rules):
  - For known vendor:product:interface tuples, set ID_MM_PORT_IGNORE
    so ModemManager keeps off the NMEA port, and add
    SYMLINK+="gps%n" so gpsd's existing udev hook picks up the
    device automatically.
  - Interface-number match uses ENV{ID_USB_INTERFACE_NUM} rather
    than ATTRS{bInterfaceNumber}: udev requires all ATTRS{} matches
    in a rule to share one parent, but idVendor/idProduct live on
    the USB device while bInterfaceNumber lives on the USB
    interface.  ENV{} matching has no parent constraint and udev
    already populates ID_USB_INTERFACE_NUM from bInterfaceNumber.
  - Initial entries: Quectel EM05 (2c7c:0125), EM06-E (2c7c:0306),
    EM12-G (2c7c:0512), Sierra Wireless EM7565 (1199:9091).
    Easy to extend.

modemd (modemd/__init__.py):
  - GPS_AT_COMMANDS table maps manufacturer -> (enable, disable) AT
    command pair.  prepare_location() issues the vendor AT command
    via 'mmcli --command=AT+QGPS=1' (or AT+CGPS=1 for Sierra)
    instead of --location-enable-gps-{nmea,raw}.  Vendor lookup is
    substring-based ('Quectel' matches both 'Quectel' and 'Quectel
    Incorporated') because ModemManager normalises differently
    across firmware revisions.  For unrecognised vendors the
    high-level MM path is still used as a fallback, so nothing
    regresses for hardware not yet in the table.
  - The AT path runs based on the udev/vendor table, not on MM's
    --location-status capabilities.  Setting ID_MM_PORT_IGNORE on
    the NMEA port removes 'gps' from MM's capability list even
    though the GPS hardware is still there, so a capability gate
    would mistakenly skip GPS for the very modems we're targeting.
  - _location_capabilities() filters MM-managed sources so a single
    unsupported flag (e.g. CDMA on an LTE-only modem) doesn't fail
    the whole batched call.  Sources the modem doesn't support are
    silently skipped; a warning is logged only if the user's YANG
    config explicitly lists one.
  - Subprocess fan-out collapsed: agps-msa, agps-msb, 3gpp and cdma
    flags share a single batched mmcli invocation.
    prepare_location() drops from 5 subprocess calls to 1 (unknown
    vendor) or 2 (known vendor, AT + batched MM).
  - Stringly-typed if/elif source dispatch replaced with a
    dict-driven table (LOCATION_MM_FLAGS).
  - Two helpers eliminate the ['mmcli', '-m', self.path, ...]
    boilerplate at ~30 ModemThread call sites:
      self._mmcli(*args, check=True)   # runcmd wrapper
      self._mmclij(*args)              # runcmdj wrapper

build (package/feature-modem/Config.in):
  - Select BR2_PACKAGE_MODEM_MANAGER_ATVIADBUS so ModemManager
    accepts raw AT commands over D-Bus without being started in
    --debug mode.  Required by the AT path above; without it
    'mmcli --command' is rejected with MM_CORE_ERROR_UNAUTHORIZED.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
2026-06-07 20:51:03 +02:00
2022-12-05 21:09:05 +01:00

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lo              ethernet   UP          00:00:00:00:00:00
                ipv4                   127.0.0.1/8 (static)
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eth0            ethernet   UP          52:54:00:12:34:56
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