netdev - Re: [PATCH] net: dsa: lan9303: handle hwaccel VLAN tags

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Date:   Tue, 15 Feb 2022 22:36:06 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Mans Rullgard <mans@...sr.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Juergen Borleis <jbe@...gutronix.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: lan9303: handle hwaccel VLAN tags

On Tue, Feb 15, 2022 at 02:59:13PM +0000, Mans Rullgard wrote:
> Check for a hwaccel VLAN tag on rx and use it if present.  Otherwise,
> use __skb_vlan_pop() like the other tag parsers do.  This fixes the case
> where the VLAN tag has already been consumed by the master.
> 
> Signed-off-by: Mans Rullgard <mans@...sr.com>
> ---
>  net/dsa/tag_lan9303.c | 21 +++++++--------------
>  1 file changed, 7 insertions(+), 14 deletions(-)
> 
> diff --git a/net/dsa/tag_lan9303.c b/net/dsa/tag_lan9303.c
> index cb548188f813..7fe180941ac4 100644
> --- a/net/dsa/tag_lan9303.c
> +++ b/net/dsa/tag_lan9303.c
> @@ -77,7 +77,6 @@ static struct sk_buff *lan9303_xmit(struct sk_buff *skb, struct net_device *dev)
>  
>  static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev)
>  {
> -	__be16 *lan9303_tag;
>  	u16 lan9303_tag1;
>  	unsigned int source_port;
>  
> @@ -87,14 +86,15 @@ static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev)
>  		return NULL;
>  	}
>  
> -	lan9303_tag = dsa_etype_header_pos_rx(skb);
> -
> -	if (lan9303_tag[0] != htons(ETH_P_8021Q)) {
> -		dev_warn_ratelimited(&dev->dev, "Dropping packet due to invalid VLAN marker\n");
> -		return NULL;
> +	skb_push_rcsum(skb, ETH_HLEN);
> +	if (skb_vlan_tag_present(skb)) {
> +		lan9303_tag1 = skb_vlan_tag_get(skb);
> +		__vlan_hwaccel_clear_tag(skb);
> +	} else {
> +		__skb_vlan_pop(skb, &lan9303_tag1);

Sorry for the bad example, there is no reason to call skb_push_rcsum()
and skb_pull_rcsum() if we go through the skb_vlan_tag_present() code
path, just the "else" branch.

>  	}
> +	skb_pull_rcsum(skb, ETH_HLEN);
>  
> -	lan9303_tag1 = ntohs(lan9303_tag[1]);
>  	source_port = lan9303_tag1 & 0x3;
>  
>  	skb->dev = dsa_master_find_slave(dev, 0, source_port);
> @@ -103,13 +103,6 @@ static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev)
>  		return NULL;
>  	}
>  
> -	/* remove the special VLAN tag between the MAC addresses
> -	 * and the current ethertype field.
> -	 */
> -	skb_pull_rcsum(skb, 2 + 2);
> -
> -	dsa_strip_etype_header(skb, LAN9303_TAG_LEN);
> -
>  	if (!(lan9303_tag1 & LAN9303_TAG_RX_TRAPPED_TO_CPU))
>  		dsa_default_offload_fwd_mark(skb);
>  
> -- 
> 2.35.1
>