[PATCH net] net: dsa: lantiq_gswip: fix maximum frame length

Currently, outgoing packets larger than 1496 bytes are dropped when
tagged VLAN is used on a switch port.

Add the frame check sequence length to the value of the register
GSWIP_MAC_FLEN to fix this. This matches the lantiq_ppa vendor driver,
which uses a value consisting of 1518 bytes for the MAC frame, plus the
lengths of special tag and VLAN tags.

Fixes: 14fceff4771e ("net: dsa: Add Lantiq / Intel DSA driver for vrx200")
Cc: stable@vger.kernel.org
Signed-off-by: Jan Hoffmann <redacted>
---
 drivers/net/dsa/lantiq_gswip.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/lantiq_gswip.c b/drivers/net/dsa/lantiq_gswip.c
index e78026ef6d8c..64d6dfa83122 100644
--- a/drivers/net/dsa/lantiq_gswip.c
+++ b/drivers/net/dsa/lantiq_gswip.c

@@ -843,7 +843,8 @@ static int gswip_setup(struct dsa_switch *ds)
 
 	gswip_switch_mask(priv, 0, GSWIP_MAC_CTRL_2_MLEN,
 			  GSWIP_MAC_CTRL_2p(cpu_port));
-	gswip_switch_w(priv, VLAN_ETH_FRAME_LEN + 8, GSWIP_MAC_FLEN);
+	gswip_switch_w(priv, VLAN_ETH_FRAME_LEN + 8 + ETH_FCS_LEN,
+		       GSWIP_MAC_FLEN);
 	gswip_switch_mask(priv, 0, GSWIP_BM_QUEUE_GCTRL_GL_MOD,
 			  GSWIP_BM_QUEUE_GCTRL);
 

-- 
2.33.0

On 9/1/21 8:49 PM, Jan Hoffmann wrote:

Currently, outgoing packets larger than 1496 bytes are dropped when
tagged VLAN is used on a switch port.

Add the frame check sequence length to the value of the register
GSWIP_MAC_FLEN to fix this. This matches the lantiq_ppa vendor driver,
which uses a value consisting of 1518 bytes for the MAC frame, plus the
lengths of special tag and VLAN tags.

This field is the size of the Ethernet Frame which probably includes the 
FCS which your patch adds.

There is also a discussion in the OpenWrt github about the same topic: 
https://github.com/openwrt/openwrt/pull/4353

Fixes: 14fceff4771e ("net: dsa: Add Lantiq / Intel DSA driver for vrx200")
Cc: stable@vger.kernel.org
Signed-off-by: Jan Hoffmann <redacted>

Acked-by: Hauke Mehrtens <hauke@hauke-m.de>

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Wed,  1 Sep 2021 20:49:33 +0200 you wrote:

Currently, outgoing packets larger than 1496 bytes are dropped when
tagged VLAN is used on a switch port.

Add the frame check sequence length to the value of the register
GSWIP_MAC_FLEN to fix this. This matches the lantiq_ppa vendor driver,
which uses a value consisting of 1518 bytes for the MAC frame, plus the
lengths of special tag and VLAN tags.

[...]

Here is the summary with links:
  - [net] net: dsa: lantiq_gswip: fix maximum frame length
    https://git.kernel.org/netdev/net/c/552799f8b3b0

You are awesome, thank you!
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