Commit 5bb6f6e1 authored by Bjørn Mork's avatar Bjørn Mork Committed by Greg Kroah-Hartman

cdc_ncm: workaround for EM7455 "silent" data interface

[ Upstream commit c086e709 ]

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>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3197832b
......@@ -438,6 +438,13 @@ int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_
if (cdc_ncm_setup(dev))
goto error2;
/* Some firmwares need a pause here or they will silently fail
* to set up the interface properly. This value was decided
* empirically on a Sierra Wireless MC7455 running 02.08.02.00
* firmware.
*/
usleep_range(10000, 20000);
/* configure data interface */
temp = usb_set_interface(dev->udev, iface_no, data_altsetting);
if (temp) {
......
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