Ask Ubuntu Asked by Chris Watts on November 19, 2021
When enabling ModemManager, I don’t see my serial-based SIM808 FONA in the list of available modems even though I’m able to get it working with pppd
.
If I start ModemManager with service stop ModemManager && ModemManager --debug
I see that it scans past serial devices when searching for modems but for every device I see:
modem-manager: (tty/ttyO4): port's parent platform driver is not whitelisted
Looking at the source code, I see that it checks the device for the udev
flag ID_MM_PLATFORM_DRIVER_PROBE
. If this flag does not exist, the serial port will not be scanned. It also checks for the ID_MM_CANDIDATE
flag to see if it’s a supported port further up, so I know it’s at least able to read that.
So I added this flag as a new rule in a new file /etc/udev/rules.d/78-mm-uart4-enable.rules
ACTION=="add", KERNEL=="ttyO4", ENV{ID_MM_PLATFORM_DRIVER_PROBE}="1"
After reboot, I see this in udevadm info /dev/ttyO4
P: /devices/ocp.3/481a8000.serial/tty/ttyO4
N: ttyO4
E: DEVNAME=/dev/ttyO4
E: DEVPATH=/devices/ocp.3/481a8000.serial/tty/ttyO4
E: ID_MM_CANDIDATE=1
E: ID_MM_PLATFORM_DRIVER_PROBE=1
E: MAJOR=247
E: MINOR=4
E: SUBSYSTEM=tty
E: TAGS=:systemd:
E: USEC_INITIALIZED=30104
But I still get the same error from modem-manager
even though I clearly have the flag set. How do I whitelist ttyO4
correctly?
In the source code, the first check for ID_MM_CANDIDATE
is done on the port (i.e. /dev/ttyO4
). After this, ModemManager will retrieve the physical platform device (the serial port itself) which we can see is /devices/ocp.3/481a800.serial
, and then check this for the ID_MM_PLATFORM_DRIVER_PROBE
flag.
If instead the udev
rule is changed to
ACTION=="add", KERNEL=="481a800.serial", ENV{ID_MM_DEVICE_PROCESS}="1"
then ModemManager will correctly see the flag on the parent device (note: ID_MM_PLATFORM_DRIVER_PROBE doesn't exist anymore).
# udevadm info /sys/devices/ocp.3/481a8000.serial
P: /devices/ocp.3/481a8000.serial
E: DEVPATH=/devices/ocp.3/481a8000.serial
E: DRIVER=omap_uart
E: ID_MM_PLATFORM_DRIVER_PROBE=1
E: MODALIAS=of:NserialT<NULL>Cti,omap3-uart
E: OF_COMPATIBLE_0=ti,omap3-uart
E: OF_COMPATIBLE_N=1
E: OF_FULLNAME=/ocp/serial@481a8000
E: OF_NAME=serial
E: SUBSYSTEM=platform
E: USEC_INITIALIZED=990701
The device now appears in mmcli -L
and nmcli device status
.
Answered by Chris Watts on November 19, 2021
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