Will modem inhibition truly release MBIM port ?

Aleksander Morgado aleksander at aleksander.es
Thu Sep 10 09:37:05 UTC 2020

Hey Edward

>  I am implementing a new firmware update mechanism with fwupd and libmbim for new 5G modules. This new update mechanism has to use mbim port directly (The mbim port cannot be opened with the proxy flag and cannot be accessed by others during update.). I found that even if a modem is inhibited, its mbim port still couldn't be accessed without the proxy flag. I checked the log of modemmanager during inhibition. I saw the mbim port closed(but with some transaction time out) and the modem disabled. When the mbim modem was inhibited, I expected its mbim port could be accessed by others without the proxy flag but it was still required. Would you have any advice on this ? Is it possible to release mbim port when a mbim modem is inhibited ?

The device inhibition applies to ModemManager only, and the mbim-proxy
process has its own lifetime once it has been spawned. The mbim-proxy
is required to be running because the MM plugin in fwupd needs it for
QMI PDC operations using QMI over MBIM.

Why do you need to access the MBIM port directly without the proxy?
Every operation that you could do without the proxy should be doable
with the proxy as well. Which MBIM command do you need to trigger the
firmware update?

The only reason I can think of is that you're going to use a different
MBIM library/program to talk to the modem from fwupd, is that the
case? If so, why not add the necessary new messages to libmbim and use
libmbim from within the new fwupd plugin support? the MM plugin in
fwupd already requires libqmi, it could also require libmbim as well
for what it's worth.


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