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

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>

diff --git a/drivers/net/usb/cdc_mbim.c b/drivers/net/usb/cdc_mbim.c
index 8973abdec9f6bee3d849d72c3cc4c18006332f53..bdd83d95ec0aa677b8443476ef2ee66018aff701 100644 (file)
--- a/drivers/net/usb/cdc_mbim.c
+++ b/drivers/net/usb/cdc_mbim.c
@@ -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,

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 3694052714371e65d63e8ae8437d1d7d6d44a463..e8a1144c5a8bfa28c1ddca137c56c888b176ab32 100644 (file)
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -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:

diff --git a/include/linux/usb/cdc_ncm.h b/include/linux/usb/cdc_ncm.h
index 1f6526c76ee84f4068707bd0ecae16aaa25c0759..3a375d07d0dc0284441133228af266956ed94f89 100644 (file)
--- a/include/linux/usb/cdc_ncm.h
+++ b/include/linux/usb/cdc_ncm.h
@@ -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);