ixgbe: DCB, X540 devices do not respond to pause frames

DCB enabled X540 devices are not responding to pause frames
due to a missing register set that was added for these
devices that did not exist in other devices.

Signed-off-by: John Fastabend <[e-mail]>
Tested-by: Ross Brattain <[e-mail]>
Signed-off-by: Jeff Kirsher <[e-mail]>

drivers/net/ixgbe/ixgbe_dcb_82599.c

···
 		IXGBE_WRITE_REG(hw, IXGBE_FCCFG, reg);
 		/*
 		 * Enable Receive PFC
-		 * We will always honor XOFF frames we receive when
-		 * we are in PFC mode.
+		 * 82599 will always honor XOFF frames we receive when
+		 * we are in PFC mode however X540 only honors enabled
+		 * traffic classes.
 		 */
 		reg = IXGBE_READ_REG(hw, IXGBE_MFLCN);
 		reg &= ~IXGBE_MFLCN_RFCE;
 		reg |= IXGBE_MFLCN_RPFCE | IXGBE_MFLCN_DPF;
+
+		if (hw->mac.type == ixgbe_mac_X540)
+			reg |= pfc_en << IXGBE_MFLCN_RPFCE_SHIFT;
+
 		IXGBE_WRITE_REG(hw, IXGBE_MFLCN, reg);
 
 	} else {

drivers/net/ixgbe/ixgbe_type.h

···
 #define IXGBE_MFLCN_RPFCE       0x00000004 /* Receive Priority FC Enable */
 #define IXGBE_MFLCN_RFCE        0x00000008 /* Receive FC Enable */
 
+#define IXGBE_MFLCN_RPFCE_SHIFT		 4
+
 /* Multiple Receive Queue Control */
 #define IXGBE_MRQC_RSSEN                 0x00000001  /* RSS Enable */
 #define IXGBE_MRQC_MRQE_MASK                    0xF /* Bits 3:0 */