netdev - Re: [PATCH net-next 2/2] net: dsa: lan9303: Clear offload_fwd

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Date:   Mon, 13 Nov 2017 12:00:17 +0100
From:   Egil Hjelmeland <privat@...l-hjelmeland.no>
To:     andrew@...n.ch, vivien.didelot@...oirfairelinux.com,
        f.fainelli@...il.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: dsa: lan9303: Clear offload_fwd_mark
 for IGMP

On 10. nov. 2017 12:54, Egil Hjelmeland wrote:
> Now that IGMP packets no longer is flooded in HW, we want the SW bridge to
> forward packets based on bridge configuration. To make that happen,
> IGMP packets must have skb->offload_fwd_mark = 0.
> 
> Signed-off-by: Egil Hjelmeland <privat@...l-hjelmeland.no>
> ---
>   net/dsa/tag_lan9303.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/net/dsa/tag_lan9303.c b/net/dsa/tag_lan9303.c
> index 5ba01fc3c6ba..b8c5e52b2eff 100644
> --- a/net/dsa/tag_lan9303.c
> +++ b/net/dsa/tag_lan9303.c
> @@ -92,6 +92,8 @@ static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev,
>   {
>   	u16 *lan9303_tag;
>   	unsigned int source_port;
> +	u16 ether_type_nw;
> +	u8 ip_protocol;
>   
>   	if (unlikely(!pskb_may_pull(skb, LAN9303_TAG_LEN))) {
>   		dev_warn_ratelimited(&dev->dev,
> @@ -129,6 +131,17 @@ static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev,
>   	skb->offload_fwd_mark = !ether_addr_equal(skb->data - ETH_HLEN,
>   						  eth_stp_addr);
>   
> +	/* We also need IGMP packets to have skb->offload_fwd_mark = 0.
> +	 * Solving this for all conceivable situations would add more cost to
> +	 * every packet. Instead we handle just the common case:
> +	 * No VLAN tag + Ethernet II framing.
> +	 * Test least probable term first.
> +	 */
> +	ether_type_nw = lan9303_tag[2];
> +	ip_protocol = *(skb->data + 9);
> +	if (ip_protocol == IPPROTO_IGMP && ether_type_nw == htons(ETH_P_IP))
> +		skb->offload_fwd_mark = 0;
> +
>   	return skb;
>   }
>   
> 

RTFM, my bad. The lan9303 has both STP and IGMP bits in the receive tag. 
It is as simple as:

u16 lan9303_tag1 = ntohs(lan9303_tag[1]);
skb->offload_fwd_mark = !(lan9303_tag1 & 0x18);

Egil