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

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Date:   Mon, 25 Jun 2018 15:07:15 +0100
From:   Dave Stevenson <dave.stevenson@...pberrypi.org>
To:     woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        davem@...emloft.net, netdev@...r.kernel.org
Cc:     Dave Stevenson <dave.stevenson@...pberrypi.org>
Subject: [PATCH 4/4] net: lan78xx: Use s/w csum check on VLANs without tag stripping

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.stevenson@...pberrypi.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