net: cdc_ncm/cdc_mbim: rework probing of NCM/MBIM functions

The NCM class match in the cdc_mbim driver is confusing and
cause unexpected behaviour. The USB core guarantees that a
USB interface is in altsetting 0 when probing starts. This
means that devices implementing a NCM 1.0 backwards
compatible MBIM function (a "NCM/MBIM function") always hit
the NCM entry in the cdc_mbim driver match table. Such
functions will never match any of the MBIM entries.

This causes unexpeced behaviour for cases where the NCM and
MBIM entries are differet, which is currently the case for
all except Ericsson devices.

Improve the probing of NCM/MBIM functions by looking up the
device again in the cdc_mbim match table after switching to
the MBIM identity.

The shared altsetting selection is updated to better
accommodate the new probing logic, returning the preferred
altsetting for the control interface instead of the data
interface. The control interface altsetting update is moved
to the cdc_mbim driver. It is never necessary to change the
control interface altsetting for NCM.

Cc: Greg Suarez <gsuarez@smithmicro.com>
Reported by: Yu-an Shih <yshih@nvidia.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 14 deletions

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 9a2bd11943eb..d23bca57a23f 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -541,10 +541,10 @@ void cdc_ncm_unbind(struct usbnet *dev, struct usb_interface *intf)
 }
 EXPORT_SYMBOL_GPL(cdc_ncm_unbind);
 
-/* Select the MBIM altsetting iff it is preferred and available,
- * returning the number of the corresponding data interface altsetting
+/* Return the number of the MBIM control interface altsetting iff it
+ * is preferred and available,
  */
-u8 cdc_ncm_select_altsetting(struct usbnet *dev, struct usb_interface *intf)
+u8 cdc_ncm_select_altsetting(struct usb_interface *intf)
 {
 	struct usb_host_interface *alt;
 
@@ -563,15 +563,15 @@ u8 cdc_ncm_select_altsetting(struct usbnet *dev, struct usb_interface *intf)
 	 *   the rules given in section 6 (USB Device Model) of this
 	 *   specification."
 	 */
-	if (prefer_mbim && intf->num_altsetting == 2) {
+	if (intf->num_altsetting < 2)
+		return intf->cur_altsetting->desc.bAlternateSetting;
+
+	if (prefer_mbim) {
 		alt = usb_altnum_to_altsetting(intf, CDC_NCM_COMM_ALTSETTING_MBIM);
-		if (alt && cdc_ncm_comm_intf_is_mbim(alt) &&
-		    !usb_set_interface(dev->udev,
-				       intf->cur_altsetting->desc.bInterfaceNumber,
-				       CDC_NCM_COMM_ALTSETTING_MBIM))
-			return CDC_NCM_DATA_ALTSETTING_MBIM;
+		if (alt && cdc_ncm_comm_intf_is_mbim(alt))
+			return CDC_NCM_COMM_ALTSETTING_MBIM;
 	}
-	return CDC_NCM_DATA_ALTSETTING_NCM;
+	return CDC_NCM_COMM_ALTSETTING_NCM;
 }
 EXPORT_SYMBOL_GPL(cdc_ncm_select_altsetting);
 
@@ -580,12 +580,11 @@ static int cdc_ncm_bind(struct usbnet *dev, struct usb_interface *intf)
 	int ret;
 
 	/* MBIM backwards compatible function? */
-	cdc_ncm_select_altsetting(dev, intf);
-	if (cdc_ncm_comm_intf_is_mbim(intf->cur_altsetting))
+	if (cdc_ncm_select_altsetting(intf) != CDC_NCM_COMM_ALTSETTING_NCM)
 		return -ENODEV;
 
-	/* NCM data altsetting is always 1 */
-	ret = cdc_ncm_bind_common(dev, intf, 1);
+	/* The NCM data altsetting is fixed */
+	ret = cdc_ncm_bind_common(dev, intf, CDC_NCM_DATA_ALTSETTING_NCM);
 
 	/*
 	 * We should get an event when network connection is "connected" or