Subject: Re: [PATCH] net: dsa: tag_brcm: legacy: fix daisy-chained switches

From: Michal Swiatkowski <[email-masked]>
Date: Fri, 17 Mar 2023 13:26:00 +0100

On Fri, Mar 17, 2023 at 01:08:15PM +0100, Álvaro Fernández Rojas wrote:
> When BCM63xx internal switches are connected to switches with a 4-byte
> Broadcom tag, it does not identify the packet as VLAN tagged, so it adds one
> based on its PVID (which is likely 0).
> Right now, the packet is received by the BCM63xx internal switch and the 6-byte
> tag is properly processed. The next step would to decode the corresponding
> 4-byte tag. However, the internal switch adds an invalid VLAN tag after the
> 6-byte tag and the 4-byte tag handling fails.
> In order to fix this we need to remove the invalid VLAN tag after the 6-byte
> tag before passing it to the 4-byte tag decoding.
> 
> Signed-off-by: Álvaro Fernández Rojas <[email-masked]>
> ---
>  net/dsa/tag_brcm.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/net/dsa/tag_brcm.c b/net/dsa/tag_brcm.c
> index 10239daa5745..cacdafb41200 100644
> --- a/net/dsa/tag_brcm.c
> +++ b/net/dsa/tag_brcm.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/dsa/brcm.h>
>  #include <linux/etherdevice.h>
> +#include <linux/if_vlan.h>
>  #include <linux/list.h>
>  #include <linux/slab.h>
>  
> @@ -252,6 +253,7 @@ static struct sk_buff *brcm_leg_tag_xmit(struct sk_buff *skb,
>  static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
>  					struct net_device *dev)
>  {
> +	int len = BRCM_LEG_TAG_LEN;
>  	int source_port;
>  	u8 *brcm_tag;
>  
> @@ -266,12 +268,16 @@ static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
>  	if (!skb->dev)
>  		return NULL;
>  
> +	/* VLAN tag is added by BCM63xx internal switch */
> +	if (netdev_uses_dsa(skb->dev))
> +		len += VLAN_HLEN;
> +
>  	/* Remove Broadcom tag and update checksum */
> -	skb_pull_rcsum(skb, BRCM_LEG_TAG_LEN);
> +	skb_pull_rcsum(skb, len);
>  
>  	dsa_default_offload_fwd_mark(skb);
>  
> -	dsa_strip_etype_header(skb, BRCM_LEG_TAG_LEN);
> +	dsa_strip_etype_header(skb, len);
>  
>  	return skb;
>  }
LGTM, but You can add fixes tag.
Reviewed-by: Michal Swiatkowski <[email-masked]>

> -- 
> 2.30.2