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net: cdc_ncm: respect operator preferred MTU reported by MBIM

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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: Ben Chan <benchan@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ben Chan 2014-03-19 14:00:06 -07:00 • committed by David S. Miller
commit 259fef033f
2 changed files with 18 additions and 0 deletions
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17
drivers/net/usb/cdc_ncm.c
View file

@ -74,6 +74,7 @@ static int cdc_ncm_setup(struct usbnet *dev)
u8 iface_no; u8 iface_no;
int err; int err;
int eth_hlen; int eth_hlen;
u16 mbim_mtu;
u16 ntb_fmt_supported; u16 ntb_fmt_supported;
__le16 max_datagram_size; __le16 max_datagram_size;
@ -261,6 +262,14 @@ out:
/* set MTU to max supported by the device if necessary */ /* set MTU to max supported by the device if necessary */
if (dev->net->mtu > ctx->max_datagram_size - eth_hlen) if (dev->net->mtu > ctx->max_datagram_size - eth_hlen)
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; 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; ctx->mbim_desc = (const struct usb_cdc_mbim_desc *)buf;
break; 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: default:
break; break;
} }

1
include/linux/usb/cdc_ncm.h
View file

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