ltq-ptm: Support 1508-byte MTU for RFC4638

Tested with VDSL on TP-Link WD8970, I see full 1500-byte PPP data
frames, which end up being 1526 byte Ethernet frames (including
Ethernet+VLAN headers) on the wire.

Fixes: FS#210

Signed-off-by: David Woodhouse <[email protected]>

package/kernel/lantiq/ltq-ptm/src/ifxmips_ptm_adsl.c

@@ -128,6 +128,7 @@ static int ptm_stop(struct net_device *);
   static unsigned int ptm_poll(int, unsigned int);
   static int ptm_napi_poll(struct napi_struct *, int);
 static int ptm_hard_start_xmit(struct sk_buff *, struct net_device *);
+static int ptm_change_mtu(struct net_device *, int);
 static int ptm_ioctl(struct net_device *, struct ifreq *, int);
 static void ptm_tx_timeout(struct net_device *);
 
@@ -246,7 +247,7 @@ static struct net_device_ops g_ptm_netdev_ops = {
     .ndo_start_xmit      = ptm_hard_start_xmit,
     .ndo_validate_addr   = eth_validate_addr,
     .ndo_set_mac_address = eth_mac_addr,
-    .ndo_change_mtu      = eth_change_mtu,
+    .ndo_change_mtu      = ptm_change_mtu,
     .ndo_do_ioctl        = ptm_ioctl,
     .ndo_tx_timeout      = ptm_tx_timeout,
 };
@@ -451,6 +452,15 @@ PTM_HARD_START_XMIT_FAIL:
     return NETDEV_TX_OK;
 }
 
+static int ptm_change_mtu(struct net_device *dev, int mtu)
+{
+	/* Allow up to 1508 bytes, for RFC4638 */
+        if (mtu < 68 || mtu > ETH_DATA_LEN + 8)
+                return -EINVAL;
+        dev->mtu = mtu;
+        return 0;
+}
+
 static int ptm_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 {
     int ndev;

package/kernel/lantiq/ltq-ptm/src/ifxmips_ptm_vdsl.c

@@ -74,6 +74,7 @@ static int ptm_stop(struct net_device *);
   static unsigned int ptm_poll(int, unsigned int);
   static int ptm_napi_poll(struct napi_struct *, int);
 static int ptm_hard_start_xmit(struct sk_buff *, struct net_device *);
+static int ptm_change_mtu(struct net_device *, int);
 static int ptm_ioctl(struct net_device *, struct ifreq *, int);
 static void ptm_tx_timeout(struct net_device *);
 
@@ -114,7 +115,7 @@ static struct net_device_ops g_ptm_netdev_ops = {
     .ndo_start_xmit      = ptm_hard_start_xmit,
     .ndo_validate_addr   = eth_validate_addr,
     .ndo_set_mac_address = eth_mac_addr,
-    .ndo_change_mtu      = eth_change_mtu,
+    .ndo_change_mtu      = ptm_change_mtu,
     .ndo_do_ioctl        = ptm_ioctl,
     .ndo_tx_timeout      = ptm_tx_timeout,
 };
@@ -358,6 +359,15 @@ PTM_HARD_START_XMIT_FAIL:
     return 0;
 }
 
+static int ptm_change_mtu(struct net_device *dev, int mtu)
+{
+	/* Allow up to 1508 bytes, for RFC4638 */
+        if (mtu < 68 || mtu > ETH_DATA_LEN + 8)
+                return -EINVAL;
+        dev->mtu = mtu;
+        return 0;
+}
+
 static int ptm_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 {
     ASSERT(dev == g_net_dev[0], "incorrect device");