From c086e7096170390594c425114d98172bc9aceb8a Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B8rn=20Mork?= Date: Sun, 3 Jul 2016 22:24:50 +0200 Subject: [PATCH] cdc_ncm: workaround for EM7455 "silent" data interface MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 --- drivers/net/usb/cdc_ncm.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c index 53759c315b97ae..877c9516e78174 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 02.08.02.00 + * firmware. + */ + usleep_range(10000, 20000); + /* configure data interface */ temp = usb_set_interface(dev->udev, iface_no, data_altsetting); if (temp) {