diff options
authorBjørn Mork <>2016-07-03 22:24:50 +0200
committerDavid S. Miller <>2016-07-04 16:12:03 -0700
commitc086e7096170390594c425114d98172bc9aceb8a (patch)
parent3dad5424adfb346c871847d467f97dcdca64ea97 (diff)
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: Stefan Armbruster <> Reported-by: Ralph Plawetzki <> Reported-by: Andreas Fett <> Reported-by: Rasmus Lerdorf <> Reported-by: Samo Ratnik <> Reported-and-tested-by: Aleksander Morgado <> Signed-off-by: Bjørn Mork <> Signed-off-by: David S. Miller <>
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 53759c315b97..877c9516e781 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -854,6 +854,13 @@ int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_
if (cdc_ncm_init(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
+ * firmware.
+ */
+ usleep_range(10000, 20000);
/* configure data interface */
temp = usb_set_interface(dev->udev, iface_no, data_altsetting);
if (temp) {