ixgbevf: Fix code for handling timeout

The VF driver was not designed to correctly handle a message timeout.  As
a result it is possible for one bad message to invalidate all messages
following it until the part is reset.  Instead we should copy the example
in igbvf of how to handle a mailbox event and message timeout.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbevf/mbx.c

@@ -86,14 +86,17 @@ static s32 ixgbevf_poll_for_ack(struct ixgbe_hw *hw)
 static s32 ixgbevf_read_posted_mbx(struct ixgbe_hw *hw, u32 *msg, u16 size)
 {
 	struct ixgbe_mbx_info *mbx = &hw->mbx;
-	s32 ret_val = IXGBE_ERR_MBX;
+	s32 ret_val = -IXGBE_ERR_MBX;
+
+	if (!mbx->ops.read)
+		goto out;
 
 	ret_val = ixgbevf_poll_for_msg(hw);
 
 	/* if ack received read message, otherwise we timed out */
 	if (!ret_val)
 		ret_val = mbx->ops.read(hw, msg, size);
-
+out:
 	return ret_val;
 }
 
@@ -109,7 +112,11 @@ static s32 ixgbevf_read_posted_mbx(struct ixgbe_hw *hw, u32 *msg, u16 size)
 static s32 ixgbevf_write_posted_mbx(struct ixgbe_hw *hw, u32 *msg, u16 size)
 {
 	struct ixgbe_mbx_info *mbx = &hw->mbx;
-	s32 ret_val;
+	s32 ret_val = -IXGBE_ERR_MBX;
+
+	/* exit if either we can't write or there isn't a defined timeout */
+	if (!mbx->ops.write || !mbx->timeout)
+		goto out;
 
 	/* send msg */
 	ret_val = mbx->ops.write(hw, msg, size);
@@ -117,7 +124,7 @@ static s32 ixgbevf_write_posted_mbx(struct ixgbe_hw *hw, u32 *msg, u16 size)
 	/* if msg sent wait until we receive an ack */
 	if (!ret_val)
 		ret_val = ixgbevf_poll_for_ack(hw);
-
+out:
 	return ret_val;
 }