[PATCH v3 2/3] rndis_host: enable the bogus MAC fixup for ZTE devices from cdc_ether

[Lech Perczak <lech.perczak@gmail.com>]

Certain ZTE modems, namely: MF823. MF831, MF910, built-in modem from
MF286R, expose both CDC-ECM and RNDIS network interfaces.
They have a trait of ignoring the locally-administered MAC address
configured on the interface both in CDC-ECM and RNDIS part,
and this leads to dropping of incoming traffic by the host.
However, the workaround was only present in CDC-ECM, and MF286R
explicitly requires it in RNDIS mode.

Re-use the workaround in rndis_host as well, to fix operation of MF286R
module, some versions of which expose only the RNDIS interface. Do so by
introducing new flag, RNDIS_DRIVER_DATA_DST_MAC_FIXUP, and testing for it
in rndis_rx_fixup. This is required, as RNDIS uses frame batching, and all
of the packets inside the batch need the fixup. This might introduce a
performance penalty, because test is done for every returned Ethernet
frame.

Apply the workaround to both "flavors" of RNDIS interfaces, as older ZTE
modems, like MF823 found in the wild, report the USB_CLASS_COMM class
interfaces, while MF286R reports USB_CLASS_WIRELESS_CONTROLLER.

Suggested-by: Bjørn Mork <bjorn@mork.no>
Cc: Kristian Evensen <kristian.evensen@gmail.com>
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
---

v3:
- Fixed wrong identifier commit description.
- Removed one unneded whitespace change.

v2:
- Ensured that MAC fixup is applied to all Ethernet frames inside an
  RNDIS batch. Thanks to Bjørn for finding the issue. 
- Introduced new driver flag to facilitate the above.

 drivers/net/usb/rndis_host.c   | 32 ++++++++++++++++++++++++++++++++
 include/linux/usb/rndis_host.h |  1 +
 2 files changed, 33 insertions(+)

diff --git a/drivers/net/usb/rndis_host.c b/drivers/net/usb/rndis_host.c
index 247f58cb0f84..7a9ece2de2c5 100644
--- a/drivers/net/usb/rndis_host.c
+++ b/drivers/net/usb/rndis_host.c
@@ -485,10 +485,14 @@ EXPORT_SYMBOL_GPL(rndis_unbind);
  */
 int rndis_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 {
+	bool dst_mac_fixup;
+
 	/* This check is no longer done by usbnet */
 	if (skb->len < dev->net->hard_header_len)
 		return 0;
 
+	dst_mac_fixup = !!(dev->driver_info->data & RNDIS_DRIVER_DATA_DST_MAC_FIXUP);
+
 	/* peripheral may have batched packets to us... */
 	while (likely(skb->len)) {
 		struct rndis_data_hdr	*hdr = (void *)skb->data;
@@ -523,10 +527,17 @@ int rndis_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 			break;
 		skb_pull(skb, msg_len - sizeof *hdr);
 		skb_trim(skb2, data_len);
+
+		if (unlikely(dst_mac_fixup))
+			usbnet_cdc_zte_rx_fixup(dev, skb2);
+
 		usbnet_skb_return(dev, skb2);
 	}
 
 	/* caller will usbnet_skb_return the remaining packet */
+	if (unlikely(dst_mac_fixup))
+		usbnet_cdc_zte_rx_fixup(dev, skb);
+
 	return 1;
 }
 EXPORT_SYMBOL_GPL(rndis_rx_fixup);
@@ -600,6 +611,17 @@ static const struct driver_info	rndis_poll_status_info = {
 	.tx_fixup =	rndis_tx_fixup,
 };
 
+static const struct driver_info	zte_rndis_info = {
+	.description =	"ZTE RNDIS device",
+	.flags =	FLAG_ETHER | FLAG_POINTTOPOINT | FLAG_FRAMING_RN | FLAG_NO_SETINT,
+	.data =		RNDIS_DRIVER_DATA_DST_MAC_FIXUP,
+	.bind =		rndis_bind,
+	.unbind =	rndis_unbind,
+	.status =	rndis_status,
+	.rx_fixup =	rndis_rx_fixup,
+	.tx_fixup =	rndis_tx_fixup,
+};
+
 /*-------------------------------------------------------------------------*/
 
 static const struct usb_device_id	products [] = {
@@ -613,6 +635,16 @@ static const struct usb_device_id	products [] = {
 	USB_VENDOR_AND_INTERFACE_INFO(0x238b,
 				      USB_CLASS_COMM, 2 /* ACM */, 0x0ff),
 	.driver_info = (unsigned long)&rndis_info,
+}, {
+	/* ZTE WWAN modules */
+	USB_VENDOR_AND_INTERFACE_INFO(0x19d2,
+				      USB_CLASS_WIRELESS_CONTROLLER, 1, 3),
+	.driver_info = (unsigned long)&zte_rndis_info,
+}, {
+	/* ZTE WWAN modules, ACM flavour */
+	USB_VENDOR_AND_INTERFACE_INFO(0x19d2,
+				      USB_CLASS_COMM, 2 /* ACM */, 0x0ff),
+	.driver_info = (unsigned long)&zte_rndis_info,
 }, {
 	/* RNDIS is MSFT's un-official variant of CDC ACM */
 	USB_INTERFACE_INFO(USB_CLASS_COMM, 2 /* ACM */, 0x0ff),
diff --git a/include/linux/usb/rndis_host.h b/include/linux/usb/rndis_host.h
index 809bccd08455..cc42db51bbba 100644
--- a/include/linux/usb/rndis_host.h
+++ b/include/linux/usb/rndis_host.h
@@ -197,6 +197,7 @@ struct rndis_keepalive_c {	/* IN (optionally OUT) */
 
 /* Flags for driver_info::data */
 #define RNDIS_DRIVER_DATA_POLL_STATUS	1	/* poll status before control */
+#define RNDIS_DRIVER_DATA_DST_MAC_FIXUP	2	/* device ignores configured MAC address */
 
 extern void rndis_status(struct usbnet *dev, struct urb *urb);
 extern int
-- 
2.30.2