Patch "cdc_ncm: workaround for EM7455 "silent" data interface" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

cdc_ncm: workaround for EM7455 "silent" data interface

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cdc_ncm-workaround-for-em7455-silent-data-interface.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Bj=C3=B8rn=20Mork?= <[email protected]>
Date: Sun, 3 Jul 2016 22:24:50 +0200
Subject: cdc_ncm: workaround for EM7455 "silent" data interface
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From: =?UTF-8?q?Bj=C3=B8rn=20Mork?= <[email protected]>

[ Upstream commit c086e7096170390594c425114d98172bc9aceb8a ]

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.

---
 drivers/net/usb/cdc_ncm.c |    7 +++++++
 1 file changed, 7 insertions(+)

@@ -809,6 +809,13 @@ int cdc_ncm_bind_common(struct usbnet *d
 	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) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/cdc_ncm-workaround-for-em7455-silent-data-interface.patch