[PATCH 4/4] net: lan78xx: Use s/w csum check on VLANs without tag stripping

[Dave Stevenson]

Observations of VLANs dropping packets due to invalid
checksums when not offloading VLAN tag receive.
With VLAN tag stripping enabled no issue is observed.

Drop back to s/w checksums if VLAN offload is disabled.

Signed-off-by: Dave Stevenson <dave.steven...@raspberrypi.org>
---
 drivers/net/usb/lan78xx.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
index f72a8f5..6f2ea84 100644
--- a/drivers/net/usb/lan78xx.c
+++ b/drivers/net/usb/lan78xx.c
@@ -3052,8 +3052,13 @@ static void lan78xx_rx_csum_offload(struct lan78xx_net 
*dev,
                                    struct sk_buff *skb,
                                    u32 rx_cmd_a, u32 rx_cmd_b)
 {
+       /* HW Checksum offload appears to be flawed if used when not stripping
+        * VLAN headers. Drop back to S/W checksums under these conditions.
+        */
        if (!(dev->net->features & NETIF_F_RXCSUM) ||
-           unlikely(rx_cmd_a & RX_CMD_A_ICSM_)) {
+           unlikely(rx_cmd_a & RX_CMD_A_ICSM_) ||
+           ((rx_cmd_a & RX_CMD_A_FVTG_) &&
+            !(dev->net->features & NETIF_F_HW_VLAN_CTAG_RX))) {
                skb->ip_summed = CHECKSUM_NONE;
        } else {
                skb->csum = ntohs((u16)(rx_cmd_b >> RX_CMD_B_CSUM_SHIFT_));
-- 
2.7.4