ixgbe: make sure FCoE DDP user buffers are really released by the HW

When invalidating the DDP context is invalidated, the HW may not be done
with the user buffer right away. In which case, we poll the FCBUFF register
to check if the buffer valid bit is cleared or not, if not, we wait for max
100us that is guaranteed by the HW.
Signed-off-by: NYi Zou <yi.zou@intel.com>
Tested-by: NRoss Brattain <ross.b.brattain@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ixgbe/ixgbe_fcoe.c

@@ -92,6 +92,7 @@ int ixgbe_fcoe_ddp_put(struct net_device *netdev, u16 xid)
 	struct ixgbe_fcoe *fcoe;
 	struct ixgbe_adapter *adapter;
 	struct ixgbe_fcoe_ddp *ddp;
+	u32 fcbuff;
 
 	if (!netdev)
 		goto out_ddp_put;
@@ -115,7 +116,14 @@ int ixgbe_fcoe_ddp_put(struct net_device *netdev, u16 xid)
 		IXGBE_WRITE_REG(&adapter->hw, IXGBE_FCBUFF, 0);
 		IXGBE_WRITE_REG(&adapter->hw, IXGBE_FCDMARW,
 				(xid | IXGBE_FCDMARW_WE));
+
+		/* guaranteed to be invalidated after 100us */
+		IXGBE_WRITE_REG(&adapter->hw, IXGBE_FCDMARW,
+				(xid | IXGBE_FCDMARW_RE));
+		fcbuff = IXGBE_READ_REG(&adapter->hw, IXGBE_FCBUFF);
 		spin_unlock_bh(&fcoe->lock);
+		if (fcbuff & IXGBE_FCBUFF_VALID)
+			udelay(100);
 	}
 	if (ddp->sgl)
 		pci_unmap_sg(adapter->pdev, ddp->sgl, ddp->sgc,