e1000: fix panic on large frame receive when mtu=default

A panic was reported when receiving 1522 size packets if using
the default MTU. we should set the initial rx buffer length to the
value that e1000changemtu sets so that we can receive any packet
that would not be dropped by LPE=0.
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke.jan.h.kok@intel.com>

drivers/net/e1000/e1000.h

@@ -110,6 +110,9 @@ struct e1000_adapter;
 #define E1000_MIN_RXD                       80
 #define E1000_MAX_82544_RXD               4096
 
+/* this is the size past which hardware will drop packets when setting LPE=0 */
+#define MAXIMUM_ETHERNET_VLAN_SIZE 1522
+
 /* Supported Rx Buffer Sizes */
 #define E1000_RXBUFFER_128   128    /* Used for packet split */
 #define E1000_RXBUFFER_256   256    /* Used for packet split */

drivers/net/e1000/e1000_main.c

@@ -1068,7 +1068,7 @@ e1000_sw_init(struct e1000_adapter *adapter)
 
 	pci_read_config_word(pdev, PCI_COMMAND, &hw->pci_cmd_word);
 
-	adapter->rx_buffer_len = MAXIMUM_ETHERNET_FRAME_SIZE;
+	adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE;
 	adapter->rx_ps_bsize0 = E1000_RXBUFFER_128;
 	hw->max_frame_size = netdev->mtu +
 			     ENET_HEADER_SIZE + ETHERNET_FCS_SIZE;
@@ -3148,7 +3148,6 @@ e1000_change_mtu(struct net_device *netdev, int new_mtu)
 		adapter->rx_buffer_len = E1000_RXBUFFER_16384;
 
 	/* adjust allocation if LPE protects us, and we aren't using SBP */
-#define MAXIMUM_ETHERNET_VLAN_SIZE 1522
 	if (!adapter->hw.tbi_compatibility_on &&
 	    ((max_frame == MAXIMUM_ETHERNET_FRAME_SIZE) ||
 	     (max_frame == MAXIMUM_ETHERNET_VLAN_SIZE)))