[SCSI] fcoe: Use NETIF_F_FCOE_MTU flag to set up max frame size (lport->mfs)

Add a define of FCOE_MTU as 2158 bytes and use FCOE_MTU when the LLD is found
to support NETIF_F_FCOE_MTU. The lport->mfs is then calculated out of the
2158 FCOE_MTU. Otherwise, we stick with the netdev->mtu, i.e., LAN MTU. Also,
change the notification on NETDEV_CHANGEMTU event to bypass changing mfs when
LAN MTU is changed if NETIF_F_FCOE_MTU is supported.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

2 files changed, 14 insertions, 2 deletions

diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
index 8702c8d728dd..c66b9fa7d674 100644
--- a/drivers/scsi/fcoe/fcoe.c
+++ b/drivers/scsi/fcoe/fcoe.c
@@ -439,8 +439,12 @@ static int fcoe_netdev_config(struct fc_lport *lp, struct net_device *netdev)
          * user-configured limit.  If the MFS is too low, fcoe_link_ok()
          * will return 0, so do this first.
          */
-        mfs = netdev->mtu - (sizeof(struct fcoe_hdr) +
-                             sizeof(struct fcoe_crc_eof));
+        mfs = netdev->mtu;
+        if (netdev->features & NETIF_F_FCOE_MTU) {
+                mfs = FCOE_MTU;
+                FCOE_NETDEV_DBG(netdev, "Supports FCOE_MTU of %d bytes\n", mfs);
+        }
+        mfs -= (sizeof(struct fcoe_hdr) + sizeof(struct fcoe_crc_eof));
         if (fc_set_mfs(lp, mfs))
                 return -EINVAL;
 
@@ -1570,6 +1574,8 @@ static int fcoe_device_notification(struct notifier_block *notifier,
         case NETDEV_CHANGE:
                 break;
         case NETDEV_CHANGEMTU:
+                if (netdev->features & NETIF_F_FCOE_MTU)
+                        break;
                 mfs = netdev->mtu - (sizeof(struct fcoe_hdr) +
                                      sizeof(struct fcoe_crc_eof));
                 if (mfs >= FC_MIN_MAX_FRAME)
diff --git a/drivers/scsi/fcoe/fcoe.h b/drivers/scsi/fcoe/fcoe.h
index ce7f60fb1bc0..c578082aef8b 100644
--- a/drivers/scsi/fcoe/fcoe.h
+++ b/drivers/scsi/fcoe/fcoe.h
@@ -40,6 +40,12 @@
 #define FCOE_MIN_XID            0x0000  /* the min xid supported by fcoe_sw */
 #define FCOE_MAX_XID            0x0FFF  /* the max xid supported by fcoe_sw */
 
+/*
+ * Max MTU for FCoE: 14 (FCoE header) + 24 (FC header) + 2112 (max FC payload)
+ * + 4 (FC CRC) + 4 (FCoE trailer) =  2158 bytes
+ */
+#define FCOE_MTU        2158
+
 unsigned int fcoe_debug_logging;
 module_param_named(debug_logging, fcoe_debug_logging, int, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(debug_logging, "a bit mask of logging levels");