ixgbe: PFC not cleared on X540 devices

X540 devices do not clear PFC before sets. This results in
the device possibly responding to PFC frames that the user
has disabled. Although it would also be wrong for the peer
to be transmitting these frames. Now we clear the register
before set.
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_dcb_82599.c

@@ -252,8 +252,10 @@ s32 ixgbe_dcb_config_pfc_82599(struct ixgbe_hw *hw, u8 pfc_en)
 		reg &= ~IXGBE_MFLCN_RFCE;
 		reg |= IXGBE_MFLCN_RPFCE | IXGBE_MFLCN_DPF;
 
-		if (hw->mac.type == ixgbe_mac_X540)
+		if (hw->mac.type == ixgbe_mac_X540) {
+			reg &= ~IXGBE_MFLCN_RPFCE_MASK;
 			reg |= pfc_en << IXGBE_MFLCN_RPFCE_SHIFT;
+		}
 
 		IXGBE_WRITE_REG(hw, IXGBE_MFLCN, reg);
 

drivers/net/ethernet/intel/ixgbe/ixgbe_type.h

@@ -1834,6 +1834,7 @@ enum {
 #define IXGBE_MFLCN_DPF         0x00000002 /* Discard Pause Frame */
 #define IXGBE_MFLCN_RPFCE       0x00000004 /* Receive Priority FC Enable */
 #define IXGBE_MFLCN_RFCE        0x00000008 /* Receive FC Enable */
+#define IXGBE_MFLCN_RPFCE_MASK	0x00000FE0 /* Receive FC Mask */
 
 #define IXGBE_MFLCN_RPFCE_SHIFT		 4