i40e: check for possible incorrect ipv6 checksum

If the IPV6EXADD bit is set in the Rx descriptor status, there
was an optional extension header with an alternate IP address
detected.  The HW checksum offload doesn't handle the alternate
IP address correctly so likely comes up with the wrong answer.
Thus, if the bit is set we ignore the checksum offload value.

Change-ID: I70ff8d38cdcddccf44107691cae13d0c07c284c8
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -892,6 +892,10 @@ static inline void i40e_rx_checksum(struct i40e_vsi *vsi,
 	      rx_status & (1 << I40E_RX_DESC_STATUS_L3L4P_SHIFT)))
 		return;
 
+	/* likely incorrect csum if alternate IP extention headers found */
+	if (rx_status & (1 << I40E_RX_DESC_STATUS_IPV6EXADD_SHIFT))
+		return;
+
 	/* IP or L4 or outmost IP checksum error */
 	if (rx_error & ((1 << I40E_RX_DESC_ERROR_IPE_SHIFT) |
 			(1 << I40E_RX_DESC_ERROR_L4E_SHIFT) |

drivers/net/ethernet/intel/i40e/i40e_type.h

@@ -499,7 +499,9 @@ enum i40e_rx_desc_status_bits {
 	I40E_RX_DESC_STATUS_FLM_SHIFT		= 11,
 	I40E_RX_DESC_STATUS_FLTSTAT_SHIFT	= 12, /* 2 BITS */
 	I40E_RX_DESC_STATUS_LPBK_SHIFT		= 14,
-	I40E_RX_DESC_STATUS_UDP_0_SHIFT		= 16
+	I40E_RX_DESC_STATUS_IPV6EXADD_SHIFT	= 15,
+	I40E_RX_DESC_STATUS_RESERVED_SHIFT	= 16, /* 2 BITS */
+	I40E_RX_DESC_STATUS_UDP_0_SHIFT		= 18
 };
 
 #define I40E_RXD_QW1_STATUS_TSYNINDX_SHIFT   I40E_RX_DESC_STATUS_TSYNINDX_SHIFT