netdev - Re: [PATCH 01/14] net: ethernet: mtk_eth_soc: account for vlan in rx header length

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Date:   Mon, 7 Nov 2022 22:55:53 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Felix Fietkau <nbd@....name>
Cc:     netdev@...r.kernel.org, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/14] net: ethernet: mtk_eth_soc: account for vlan in rx
 header length

On Mon, Nov 07, 2022 at 07:54:39PM +0100, Felix Fietkau wrote:
> This may be needed for correct MTU settings on devices using DSA
> 
> Signed-off-by: Felix Fietkau <nbd@....name>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> index 589f27ddc401..dcf2a0d5da33 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
> @@ -29,7 +29,7 @@
>  #define MTK_TX_DMA_BUF_LEN_V2	0xffff
>  #define MTK_DMA_SIZE		512
>  #define MTK_MAC_COUNT		2
> -#define MTK_RX_ETH_HLEN		(ETH_HLEN + ETH_FCS_LEN)
> +#define MTK_RX_ETH_HLEN		(VLAN_ETH_HLEN + ETH_HLEN + ETH_FCS_LEN)

Commit title says account for VLAN (VLAN_HLEN, 4 bytes), code says add
VLAN_ETH_HLEN (18) more bytes.

Also, why is DSA mentioned in the commit message? Is accounting for VLAN
hlen not needed if DSA is not used? Why?

>  #define MTK_RX_HLEN		(NET_SKB_PAD + MTK_RX_ETH_HLEN + NET_IP_ALIGN)
>  #define MTK_DMA_DUMMY_DESC	0xffffffff
>  #define MTK_DEFAULT_MSG_ENABLE	(NETIF_MSG_DRV | \
> -- 
> 2.38.1
>