[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 <jan@3e8.eu>
---
 drivers/net/dsa/lantiq_gswip.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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 <jan@3e8.eu>

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

> ---
>   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);
>   
>

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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