cdc_ncm: Add support for moving NDP to end of NCM frame

NCM specs are not actually mandating a specific position in the frame for
the NDP (Network Datagram Pointer). However, some Huawei devices will
ignore our aggregates if it is not placed after the datagrams it points
to. Add support for doing just this, in a per-device configurable way.
While at it, update NCM subdrivers, disabling this functionality in all of
them, except in huawei_cdc_ncm where it is enabled instead.
We aren't making any distinction between different Huawei NCM devices,
based on what the vendor driver does. Standard NCM devices are left
unaffected: if they are compliant, they should be always usable, still
stay on the safe side.

This change has been tested and working with a Huawei E3131 device (which
works regardless of NDP position), a Huawei E3531 (also working both
ways) and an E3372 (which mandates NDP to be after indexed datagrams).

V1->V2:
- corrected wrong NDP acronym definition
- fixed possible NULL pointer dereference
- patch cleanup
V2->V3:
- Properly account for the NDP size when writing new packets to SKB

Signed-off-by: Enrico Mioso <mrkiko.rs@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/net/usb/huawei_cdc_ncm.c b/drivers/net/usb/huawei_cdc_ncm.c
index 735f7dadb9a0..2680a65cd5e4 100644
--- a/drivers/net/usb/huawei_cdc_ncm.c
+++ b/drivers/net/usb/huawei_cdc_ncm.c
@@ -73,11 +73,14 @@ static int huawei_cdc_ncm_bind(struct usbnet *usbnet_dev,
 	struct usb_driver *subdriver = ERR_PTR(-ENODEV);
 	int ret = -ENODEV;
 	struct huawei_cdc_ncm_state *drvstate = (void *)&usbnet_dev->data;
+	int drvflags = 0;
 
 	/* altsetting should always be 1 for NCM devices - so we hard-coded
-	 * it here
+	 * it here. Some huawei devices will need the NDP part of the NCM package to
+	 * be at the end of the frame.
 	 */
-	ret = cdc_ncm_bind_common(usbnet_dev, intf, 1);
+	drvflags |= CDC_NCM_FLAG_NDP_TO_END;
+	ret = cdc_ncm_bind_common(usbnet_dev, intf, 1, drvflags);
 	if (ret)
 		goto err;