Issue with dual SIM and AUTO_SIM feature

Alexey Karyakin akaryakin at
Tue Apr 13 19:53:51 UTC 2021


This is a follow up on the recently discussed issue with EM7511 and the
AUTO-SIM feature. When the carrier is set to AUTO_SIM, the modem will
automatically set the appropriate profile, and reboot for this profile to
take effect.

A recent version of MM temporarily switches to every installed SIM during
probing, in order to retrieve SIM information. The logic is summarized in
the commit message

Unfortunately, what we observe is these two features together seem to cause
an infinite reboot loop after a SIM switch.

1. Suppose, the SIM 1 is active now and the profile set to AUTO-SIM.
2. We ask the MM to switch to SIM 2.
3. The modem reboots, on its own. The MM detects the modem disappearing and
has to cancel whatever it was doing to it.
4. When the modem comes back up, MM retrieves the slot status list and
initiates the switching loop (see uim_get_slot_status_ready()). It first
switches to SIM 1...
5. Repeat starting with step 3.

I hope there is something I am missing, but this is what it looks like.

I wonder if this is a general issue affecting any users with AUTO-SIM
enabled and also what could be a right approach to address this. Currently,
we are trying a "solution" that would disable the AUTO-SIM (switch to the
current profile) before the SIM enumeration loop, and re-enable it again
afterwards. By patching the MM.

Any ideas are appreciated.

Alexey Karyakin
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