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List:       git-commits-head
Subject:    net: cdc_ncm: avoid changing RX/TX buffers on MTU changes
From:       "Linux Kernel Mailing List" <linux-kernel () vger ! kernel ! org>
Date:       2015-12-31 22:51:34
Message-ID: 20151231225134.4816C66129C () gitolite ! kernel ! org
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Web:        https://git.kernel.org/torvalds/c/1dfddff5fcd869fcab0c52fafae099dfa435a935
                
Commit:     1dfddff5fcd869fcab0c52fafae099dfa435a935
Parent:     184fc8b5ee601cd83dbbdf3e6cfec5f5b8d3b41a
Refname:    refs/heads/master
Author:     Bjørn Mork <bjorn@mork.no>
AuthorDate: Wed Dec 23 13:42:43 2015 +0100
Committer:  David S. Miller <davem@davemloft.net>
CommitDate: Wed Dec 23 22:52:08 2015 -0500

    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>
---
 drivers/net/usb/cdc_mbim.c  |  2 +-
 drivers/net/usb/cdc_ncm.c   | 31 +++++++++++++++++++++++++++++++
 include/linux/usb/cdc_ncm.h |  1 +
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/cdc_mbim.c b/drivers/net/usb/cdc_mbim.c
index 8973abd..bdd83d9 100644
--- 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 3694052..e8a1144 100644
--- 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 1f6526c..3a375d0 100644
--- 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);
--
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