linux-kernel - [PATCH AUTOSEL for 4.15 24/78] qmi_wwan: set FLAG_SEND_ZLP to avoid network initiated disconnect

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Date:   Thu, 8 Mar 2018 04:56:11 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Bjørn Mork <bjorn@...k.no>,
        "David S . Miller" <davem@...emloft.net>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.15 24/78] qmi_wwan: set FLAG_SEND_ZLP to avoid
 network initiated disconnect

From: Bjørn Mork <bjorn@...k.no>

[ Upstream commit 245d21190aec547c0de64f70c0e6de871c185a24 ]

It has been reported that the dummy byte we add to avoid
ZLPs can be forwarded by the modem to the PGW/GGSN, and that
some operators will drop the connection if this happens.

In theory, QMI devices are based on CDC ECM and should as such
both support ZLPs and silently ignore the dummy byte.  The latter
assumption failed.  Let's test out the first.

Signed-off-by: Bjørn Mork <bjorn@...k.no>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/net/usb/qmi_wwan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
index e7114c34fe4b..76ac48095c29 100644
--- a/drivers/net/usb/qmi_wwan.c
+++ b/drivers/net/usb/qmi_wwan.c
@@ -826,7 +826,7 @@ static int qmi_wwan_resume(struct usb_interface *intf)
 
 static const struct driver_info	qmi_wwan_info = {
 	.description	= "WWAN/QMI device",
-	.flags		= FLAG_WWAN,
+	.flags		= FLAG_WWAN | FLAG_SEND_ZLP,
 	.bind		= qmi_wwan_bind,
 	.unbind		= qmi_wwan_unbind,
 	.manage_power	= qmi_wwan_manage_power,
@@ -835,7 +835,7 @@ static const struct driver_info	qmi_wwan_info = {
 
 static const struct driver_info	qmi_wwan_info_quirk_dtr = {
 	.description	= "WWAN/QMI device",
-	.flags		= FLAG_WWAN,
+	.flags		= FLAG_WWAN | FLAG_SEND_ZLP,
 	.bind		= qmi_wwan_bind,
 	.unbind		= qmi_wwan_unbind,
 	.manage_power	= qmi_wwan_manage_power,
-- 
2.14.1