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net: cdc_ncm: avoid changing RX/TX buffers on MTU changes

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NCM buffer sizes are negotiated with the device independently of
the network device MTU.  The RX buffers are allocated by the
usbnet framework based on the rx_urb_size value set by cdc_ncm. A
single RX buffer can hold a number of MTU sized packets.

The default usbnet change_mtu ndo only modifies rx_urb_size if it
is equal to hard_mtu.  And the cdc_ncm driver will set rx_urb_size
and hard_mtu independently of each other, based on dwNtbInMaxSize
and dwNtbOutMaxSize respectively. It was therefore assumed that
usbnet_change_mtu() would never touch rx_urb_size.  This failed to
consider the case where dwNtbInMaxSize and dwNtbOutMaxSize happens
to be equal.

Fix by implementing an NCM specific change_mtu ndo, modifying the
netdev MTU without touching the buffer size settings.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Bjørn Mork 2015-12-23 13:42:43 +01:00 committed by David S. Miller
parent 184fc8b5ee
commit 1dfddff5fc
3 changed files with 33 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/usb/cdc_mbim.c
View File

@ -100,7 +100,7 @@ static const struct net_device_ops cdc_mbim_netdev_ops = {
.ndo_stop = usbnet_stop,
.ndo_start_xmit = usbnet_start_xmit,
.ndo_tx_timeout = usbnet_tx_timeout,
.ndo_change_mtu = usbnet_change_mtu,
.ndo_change_mtu = cdc_ncm_change_mtu,
.ndo_set_mac_address = eth_mac_addr,
.ndo_validate_addr = eth_validate_addr,
.ndo_vlan_rx_add_vid = cdc_mbim_rx_add_vid,

31
drivers/net/usb/cdc_ncm.c
View File

@ -41,6 +41,7 @@
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/ctype.h>
#include <linux/etherdevice.h>
#include <linux/ethtool.h>
#include <linux/workqueue.h>
#include <linux/mii.h>
@ -689,6 +690,33 @@ static void cdc_ncm_free(struct cdc_ncm_ctx *ctx)
kfree(ctx);
}
/* we need to override the usbnet change_mtu ndo for two reasons:
* - respect the negotiated maximum datagram size
* - avoid unwanted changes to rx and tx buffers
*/
int cdc_ncm_change_mtu(struct net_device *net, int new_mtu)
{
struct usbnet *dev = netdev_priv(net);
struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
int maxmtu = ctx->max_datagram_size - cdc_ncm_eth_hlen(dev);
if (new_mtu <= 0 || new_mtu > maxmtu)
return -EINVAL;
net->mtu = new_mtu;
return 0;
}
EXPORT_SYMBOL_GPL(cdc_ncm_change_mtu);
static const struct net_device_ops cdc_ncm_netdev_ops = {
.ndo_open = usbnet_open,
.ndo_stop = usbnet_stop,
.ndo_start_xmit = usbnet_start_xmit,
.ndo_tx_timeout = usbnet_tx_timeout,
.ndo_change_mtu = cdc_ncm_change_mtu,
.ndo_set_mac_address = eth_mac_addr,
.ndo_validate_addr = eth_validate_addr,
};
int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_altsetting, int drvflags)
{
struct cdc_ncm_ctx *ctx;
@ -823,6 +851,9 @@ int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_
/* add our sysfs attrs */
dev->net->sysfs_groups[0] = &cdc_ncm_sysfs_attr_group;
/* must handle MTU changes */
dev->net->netdev_ops = &cdc_ncm_netdev_ops;
return 0;
error2:

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

@ -138,6 +138,7 @@ struct cdc_ncm_ctx {
};
u8 cdc_ncm_select_altsetting(struct usb_interface *intf);
int cdc_ncm_change_mtu(struct net_device *net, int new_mtu);
int cdc_ncm_bind_common(struct usbnet *dev, struct usb_interface *intf, u8 data_altsetting, int drvflags);
void cdc_ncm_unbind(struct usbnet *dev, struct usb_interface *intf);
struct sk_buff *cdc_ncm_fill_tx_frame(struct usbnet *dev, struct sk_buff *skb, __le32 sign);