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Commit c086e709 authored by Bjørn Mork's avatar Bjørn Mork Committed by David S. Miller
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cdc_ncm: workaround for EM7455 "silent" data interface



Several Lenovo users have reported problems with their Sierra
Wireless EM7455 modem. The driver has loaded successfully and
the MBIM management channel has appeared to work, including
establishing a connection to the mobile network. But no frames
have been received over the data interface.

The problem affects all EM7455 and MC7455, and is assumed to
affect other modems based on the same Qualcomm chipset and
baseband firmware.

Testing narrowed the problem down to what seems to be a
firmware timing bug during initialization. Adding a short sleep
while probing is sufficient to make the problem disappear.
Experiments have shown that 1-2 ms is too little to have any
effect, while 10-20 ms is enough to reliably succeed.

Reported-by: default avatarStefan Armbruster <ml001@armbruster-it.de>
Reported-by: default avatarRalph Plawetzki <ralph@purejava.org>
Reported-by: default avatarAndreas Fett <andreas.fett@secunet.com>
Reported-by: default avatarRasmus Lerdorf <rasmus@lerdorf.com>
Reported-by: default avatarSamo Ratnik <samo.ratnik@gmail.com>
Reported-and-tested-by: default avatarAleksander Morgado <aleksander@aleksander.es>
Signed-off-by: default avatarBjørn Mork <bjorn@mork.no>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 3dad5424
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