netdev - Re: [PATCH net] net: dsa: lantiq_gswip: fix maximum frame length

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Date:   Wed, 1 Sep 2021 23:30:48 +0200
From:   Hauke Mehrtens <hauke@...ke-m.de>
To:     Jan Hoffmann <jan@....eu>, netdev@...r.kernel.org
Cc:     stable@...r.kernel.org, Thomas Nixon <tom@...n.co.uk>
Subject: Re: [PATCH net] net: dsa: lantiq_gswip: fix maximum frame length

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@...r.kernel.org
> Signed-off-by: Jan Hoffmann <jan@....eu>

Acked-by: Hauke Mehrtens <hauke@...ke-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);
>   
> 


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