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Commit 259fef03 authored by Ben Chan's avatar Ben Chan Committed by David S. Miller
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net: cdc_ncm: respect operator preferred MTU reported by MBIM 



According to "Universal Serial Bus Communications Class Subclass
Specification for Mobile Broadband Interface Model, Revision 1.0,
Errata-1" published by USB-IF, the wMTU field of the MBIM extended
functional descriptor indicates the operator preferred MTU for IP data
streams.

This patch modifies cdc_ncm_setup to ensure that the MTU value set on
the usbnet device does not exceed the operator preferred MTU indicated
by wMTU if the MBIM device exposes a MBIM extended functional
descriptor.

Signed-off-by: default avatarBen Chan <benchan@chromium.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent bfe9b3f8

drivers/net/usb/cdc_ncm.c

+17 −0
Original line number Diff line number Diff line
@@ -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 @@ out: 
	/* 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

+1 −0
Original line number Diff line number Diff line
@@ -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;