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Subject[PATCH net-next v4 2/2] net: cdc_ncm: respect operator preferred MTU reported by MBIM
Date
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>
---
drivers/net/usb/cdc_ncm.c | 17 +++++++++++++++++
include/linux/usb/cdc_ncm.h | 1 +
2 files changed, 18 insertions(+)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index dbff290..e8711a8 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/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 @@ 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;
}
diff --git a/include/linux/usb/cdc_ncm.h b/include/linux/usb/cdc_ncm.h
index c3fa807..bdf05fb 100644
--- a/include/linux/usb/cdc_ncm.h
+++ b/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;
--
1.9.0.279.gdc9e3eb


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