netdev - Re: [PATCH v3 net] stmmac: Added support for 802.1ad S-TAG stripping

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Date:   Fri, 25 May 2018 09:34:12 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     Elad Nachman <eladv6@...il.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, peppe.cavallaro@...com,
        alexandre.torgue@...com
Subject: Re: [PATCH v3 net] stmmac: Added support for 802.1ad S-TAG stripping

On 2018/05/25 1:56, Elad Nachman wrote:
> stmmac reception handler calls stmmac_rx_vlan() to strip the vlan before calling napi_gro_receive().
> 
> The function assumes VLAN tagged frames are always tagged with 802.1Q protocol,
> and assigns ETH_P_8021Q to the skb by hard-coding the parameter on call to __vlan_hwaccel_put_tag() .
> 
> This causes packets not to be passed to the VLAN slave if it was created with 802.1AD protocol
> (ip link add link eth0 eth0.100 type vlan proto 802.1ad id 100).
> 
> This fix passes the protocol from the VLAN header into __vlan_hwaccel_put_tag()
> instead of using the hard-coded value of ETH_P_8021Q.
> NETIF_F_HW_VLAN_STAG_RX was added to the net device features to reflect this new support.
> 
> Signed-off-by: Elad Nachman <eladn@...at.com>
> 
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index b65e2d1..2d2f37f 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -3293,17 +3293,19 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
>  
>  static void stmmac_rx_vlan(struct net_device *dev, struct sk_buff *skb)
>  {
> -	struct ethhdr *ehdr;
> +	struct vlan_ethhdr *veth;
>  	u16 vlanid;
> +	__be16 vlan_proto;
>  
> -	if ((dev->features & NETIF_F_HW_VLAN_CTAG_RX) ==
> -	    NETIF_F_HW_VLAN_CTAG_RX &&
> +	if ((dev->features & (NETIF_F_HW_VLAN_CTAG_RX|NETIF_F_HW_VLAN_STAG_RX)) ==
> +	    (NETIF_F_HW_VLAN_CTAG_RX|NETIF_F_HW_VLAN_STAG_RX) &&

This is basically not a correct condition since you cannot strip CTAG if
HW_VLAN_STAG_RX is disabled even when HW_VLAN_CTAG_RX is enabled.

The correct behavior is stripping CTAG when CTAG_RX is enabled and
stripping STAG when STAG_RX is enabled, so this code cannot be
protocol-agnostic. I suggested handling only CTAG in this driver because
I thought adding STAG support will make this unnecessarily complicated.

But I now actually noticed that this driver seems not able to toggle
CTAG_RX nor STAG_RX because hw_features does not include them. So this
code should work even if the condition is wrong, but in the first place
why we need to check if dev->features includes CTAG_RX here... it's
always included. It seems removing this check will be sufficient.

>  	    !__vlan_get_tag(skb, &vlanid)) {
>  		/* pop the vlan tag */
> -		ehdr = (struct ethhdr *)skb->data;
> -		memmove(skb->data + VLAN_HLEN, ehdr, ETH_ALEN * 2);
> +		veth = (struct vlan_ethhdr *)skb->data;
> +		vlan_proto = veth->h_vlan_proto;
> +		memmove(skb->data + VLAN_HLEN, veth, ETH_ALEN * 2);
>  		skb_pull(skb, VLAN_HLEN);
> -		__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), vlanid);
> +		__vlan_hwaccel_put_tag(skb, vlan_proto, vlanid);
>  	}
>  }
>  
> @@ -4344,7 +4346,7 @@ int stmmac_dvr_probe(struct device *device,
>  	ndev->watchdog_timeo = msecs_to_jiffies(watchdog);
>  #ifdef STMMAC_VLAN_TAG_USED
>  	/* Both mac100 and gmac support receive VLAN tag detection */
> -	ndev->features |= NETIF_F_HW_VLAN_CTAG_RX;
> +	ndev->features |= (NETIF_F_HW_VLAN_CTAG_RX|NETIF_F_HW_VLAN_STAG_RX);
>  #endif
>  	priv->msg_enable = netif_msg_init(debug, default_msg_level);
>  
> 

-- 
Toshiaki Makita