Merge branch 'cdc-next'

Ben Chan says:

====================
Adjust MTU as indicated by MBIM extended functional descriptor.

The MBIM extended functional descriptor, defined in "Universal Serial Bus
Communications Class Subclass Specification for Mobile Broadband Interface
Model, Revision 1.0, Errata-1" by USB-IF, indicates the operator preferred MTU
value via a wMTU field.

This patch set ensures that the initial MTU value set by cdc_ncm on a MBIM net
device does not exceed the wMTU value, provided the MBIM device exposes a MBIM
extended functional descriptor.

* Changelog
v2: Fixed a le16_to_cpu conversion issue in patch 2/2 pointed out by
    Bjørn Mork <bjorn@mork.no>
v3: No code changes. Resubmitted to include patch 1/2 as suggested by
    David Miller <davem@davemloft.net>
v4: No code changes. Resubmitted as suggested by David Miller:
    - Added a summary of the patch set
    - Carried the ACK from Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    - Added a specified the tree (net-next) to apply the patch set to
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/cdc_ncm.c

@@ -74,6 +74,7 @@ static int cdc_ncm_setup(struct usbnet *dev)
 	u8 iface_no;
 	int err;
 	int eth_hlen;
+	u16 mbim_mtu;
 	u16 ntb_fmt_supported;
 	__le16 max_datagram_size;
 
@@ -261,6 +262,14 @@ static int cdc_ncm_setup(struct usbnet *dev)
 	/* set MTU to max supported by the device if necessary */
 	if (dev->net->mtu > ctx->max_datagram_size - eth_hlen)
 		dev->net->mtu = ctx->max_datagram_size - eth_hlen;
+
+	/* do not exceed operater preferred MTU */
+	if (ctx->mbim_extended_desc) {
+		mbim_mtu = le16_to_cpu(ctx->mbim_extended_desc->wMTU);
+		if (mbim_mtu != 0 && mbim_mtu < dev->net->mtu)
+			dev->net->mtu = mbim_mtu;
+	}
+
 	return 0;
 }
 
@@ -399,6 +408,14 @@ int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_
 			ctx->mbim_desc = (const struct usb_cdc_mbim_desc *)buf;
 			break;
 
+		case USB_CDC_MBIM_EXTENDED_TYPE:
+			if (buf[0] < sizeof(*(ctx->mbim_extended_desc)))
+				break;
+
+			ctx->mbim_extended_desc =
+				(const struct usb_cdc_mbim_extended_desc *)buf;
+			break;
+
 		default:
 			break;
 		}

include/linux/usb/cdc_ncm.h

@@ -93,6 +93,7 @@ struct cdc_ncm_ctx {
 
 	const struct usb_cdc_ncm_desc *func_desc;
 	const struct usb_cdc_mbim_desc *mbim_desc;
+	const struct usb_cdc_mbim_extended_desc *mbim_extended_desc;
 	const struct usb_cdc_ether_desc *ether_desc;
 
 	struct usb_interface *control;

include/uapi/linux/usb/cdc.h

@@ -56,6 +56,7 @@
 #define USB_CDC_OBEX_TYPE		0x15
 #define USB_CDC_NCM_TYPE		0x1a
 #define USB_CDC_MBIM_TYPE		0x1b
+#define USB_CDC_MBIM_EXTENDED_TYPE	0x1c
 
 /* "Header Functional Descriptor" from CDC spec  5.2.3.1 */
 struct usb_cdc_header_desc {
@@ -205,6 +206,17 @@ struct usb_cdc_mbim_desc {
 	__u8    bmNetworkCapabilities;
 } __attribute__ ((packed));
 
+/* "MBIM Extended Functional Descriptor" from CDC MBIM spec 1.0 errata-1 */
+struct usb_cdc_mbim_extended_desc {
+	__u8	bLength;
+	__u8	bDescriptorType;
+	__u8	bDescriptorSubType;
+
+	__le16	bcdMBIMExtendedVersion;
+	__u8	bMaxOutstandingCommandMessages;
+	__le16	wMTU;
+} __attribute__ ((packed));
+
 /*-------------------------------------------------------------------------*/
 
 /*