Re: [RFC PATCH v2 net-next 14/16] net: dsa: don't set skb->offload_fwd_mark when not offloading the bridge

On 3/18/2021 4:18 PM, Vladimir Oltean wrote:

From: Vladimir Oltean <vladimir.oltean@nxp.com>

DSA has gained the recent ability to deal gracefully with upper
interfaces it cannot offload, such as the bridge, bonding or team
drivers. When such uppers exist, the ports are still in standalone mode
as far as the hardware is concerned.

But when we deliver packets to the software bridge in order for that to
do the forwarding, there is an unpleasant surprise in that the bridge
will refuse to forward them. This is because we unconditionally set
skb->offload_fwd_mark = true, meaning that the bridge thinks the frames
were already forwarded in hardware by us.

Since dp->bridge_dev is populated only when there is hardware offload
for it, but not in the software fallback case, let's introduce a new
helper that can be called from the tagger data path which sets the
skb->offload_fwd_mark accordingly to zero when there is no hardware
offload for bridging. This lets the bridge forward packets back to other
interfaces of our switch, if needed.

Without this change, sending a packet to the CPU for an unoffloaded
interface triggers this WARN_ON:

void nbp_switchdev_frame_mark(const struct net_bridge_port *p,
			      struct sk_buff *skb)
{
	if (skb->offload_fwd_mark && !WARN_ON_ONCE(!p->offload_fwd_mark))
		BR_INPUT_SKB_CB(skb)->offload_fwd_mark = p->offload_fwd_mark;
}

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Tobias Waldekranz <tobias@waldekranz.com>

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
-- 
Florian