ixgbe: X540 devices RX PFC frames pause traffic even if disabled

Receiving PFC (priority flow control) frames while the feature
is off should not pause the traffic class. On the X540 devices
the traffic class react to frames if it was previously enabled
because the field is incorrectly cleared.

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

@@ -271,13 +271,23 @@ s32 ixgbe_dcb_config_pfc_82599(struct ixgbe_hw *hw, u8 pfc_en, u8 *prio_tc)
 		reg |= IXGBE_MFLCN_RPFCE | IXGBE_MFLCN_DPF;
 
 		if (hw->mac.type == ixgbe_mac_X540) {
-			reg &= ~(IXGBE_MFLCN_RPFCE_MASK | 0x10);
+			reg &= ~IXGBE_MFLCN_RPFCE_MASK;
 			reg |= pfc_en << IXGBE_MFLCN_RPFCE_SHIFT;
 		}
 
 		IXGBE_WRITE_REG(hw, IXGBE_MFLCN, reg);
 
 	} else {
+		/* X540 devices have a RX bit that should be cleared
+		 * if PFC is disabled on all TCs but PFC features is
+		 * enabled.
+		 */
+		if (hw->mac.type == ixgbe_mac_X540) {
+			reg = IXGBE_READ_REG(hw, IXGBE_MFLCN);
+			reg &= ~IXGBE_MFLCN_RPFCE_MASK;
+			IXGBE_WRITE_REG(hw, IXGBE_MFLCN, reg);
+		}
+
 		for (i = 0; i < MAX_TRAFFIC_CLASS; i++)
 			hw->mac.ops.fc_enable(hw, i);
 	}

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

@@ -1850,7 +1850,7 @@ 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_MASK	0x00000FF0 /* Receive FC Mask */
 
 #define IXGBE_MFLCN_RPFCE_SHIFT		 4