Issue observed on Huawei ME936 since commit 0c7f3380a

Ben Chan benchan at
Thu Feb 1 06:15:42 UTC 2018

I've been debugging an issue with Huawei ME936 (in MBIM mode). The issue is
observed since commit 0c7f3380a ("bearer-mbim: ensure session is
disconnected before trying to connect").

>From what I observe, the first connection attempt on ME936 always times out
when MMBearerMbim issues a MBIM_CID_CONNECT
(MBIMActivationCommandDeactivate) command to force deactivating a session
that hasn't yet been activated. But as MMBearerMbim currently ignores that
error, it proceeds to issue MBIM_CID_CONNECT
(MBIMActivationCommandActivate) command, which then also fails. For some
unknown reason (mostly like a firmware bug), the modem takes more than 30s
(i.e. the current timeout) to deactivate a session that hasn't been
activated once.

Increasing the timeout would address the issue, but I'm not too happy to
wait 30-40s for a unnecessary operation. So I thought I could query the
activation state of the session before trying to deactivate it.
Unfortunately, the modem always reports a "unknown" activation state if the
session hasn't been activated once (well, most likely yet another firmware

As the chance of getting a firmware fix seems slim, I try to address that
in ModemManger / libmbim with the following patches:





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