ieee1394: eth1394: allow MTU bigger than 1500

RFC 2734 says: "IP-capable nodes may operate with an MTU size larger
than the default [1500 octets], but the means by which a larger MTU is
configured are beyond the scope of this document."

Allow users to set an MTU bigger than 1500.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 19 insertions, 15 deletions

diff --git a/drivers/ieee1394/eth1394.c b/drivers/ieee1394/eth1394.c
index 8f19f5b77a59..aee82922e6b7 100644
--- a/drivers/ieee1394/eth1394.c
+++ b/drivers/ieee1394/eth1394.c
@@ -136,9 +136,6 @@ static const int hdr_type_len[] = {
         sizeof(struct eth1394_sf_hdr)
 };
 
-/* For now, this needs to be 1500, so that XP works with us */
-#define ETH1394_DATA_LEN        ETH_DATA_LEN
-
 static const u16 eth1394_speedto_maxpayload[] = {
 /*     S100, S200, S400, S800, S1600, S3200 */
         512, 1024, 2048, 4096,  4096,  4096
@@ -262,17 +259,27 @@ static void ether1394_tx_timeout(struct net_device *dev)
         ether1394_host_reset(host);
 }
 
+static inline int ether1394_max_mtu(struct hpsb_host* host)
+{
+        return (1 << (host->csr.max_rec + 1))
+                        - sizeof(union eth1394_hdr) - ETHER1394_GASP_OVERHEAD;
+}
+
 static int ether1394_change_mtu(struct net_device *dev, int new_mtu)
 {
-        int max_rec =
-                ((struct eth1394_priv *)netdev_priv(dev))->host->csr.max_rec;
+        int max_mtu;
 
-        if (new_mtu < 68 ||
-            new_mtu > ETH1394_DATA_LEN ||
-            new_mtu > (1 << (max_rec + 1)) - sizeof(union eth1394_hdr) -
-                      ETHER1394_GASP_OVERHEAD)
+        if (new_mtu < 68)
                 return -EINVAL;
 
+        max_mtu = ether1394_max_mtu(
+                        ((struct eth1394_priv *)netdev_priv(dev))->host);
+        if (new_mtu > max_mtu) {
+                ETH1394_PRINT(KERN_INFO, dev->name,
+                              "Local node constrains MTU to %d\n", max_mtu);
+                return -ERANGE;
+        }
+
         dev->mtu = new_mtu;
         return 0;
 }
@@ -476,13 +483,10 @@ static void ether1394_reset_priv(struct net_device *dev, int set_mtu)
                         max_speed = host->speed[i];
         priv->bc_sspd = max_speed;
 
-        /* We'll use our maximum payload as the default MTU */
         if (set_mtu) {
-                int max_payload = 1 << (host->csr.max_rec + 1);
-
-                dev->mtu = min(ETH1394_DATA_LEN,
-                               (int)(max_payload - sizeof(union eth1394_hdr) -
-                                     ETHER1394_GASP_OVERHEAD));
+                /* Use the RFC 2734 default 1500 octets or the maximum payload
+                 * as initial MTU */
+                dev->mtu = min(1500, ether1394_max_mtu(host));
 
                 /* Set our hardware address while we're at it */
                 memcpy(dev->dev_addr, &guid, sizeof(u64));