Re: [PATCH v4 net-next 13/15] net: dsa: add support for bridge TX forwarding offload

[Florian Fainelli <f.fainelli@gmail.com>]

On 7/18/2021 2:44 PM, Vladimir Oltean wrote:
> For a DSA switch, to offload the forwarding process of a bridge device
> means to send the packets coming from the software bridge as data plane
> packets. This is contrary to everything that DSA has done so far,
> because the current taggers only know to send control packets (ones that
> target a specific destination port), whereas data plane packets are
> supposed to be forwarded according to the FDB lookup, much like packets
> ingressing on any regular ingress port. If the FDB lookup process
> returns multiple destination ports (flooding, multicast), then
> replication is also handled by the switch hardware - the bridge only
> sends a single packet and avoids the skb_clone().
> 
> DSA plays a substantial role in backing the forwarding offload, and
> leaves relatively few things up to the switch driver. In particular, DSA
> keeps for each bridge port a zero-based index (the number of the
> bridge). Multiple ports enslaved to the same bridge have a pointer to
> the same accel_priv structure.
> 
> The tagger can check if the packet that is being transmitted on has
> skb->offload_fwd_mark = true or not. If it does, it can be sure that the
> packet belongs to the data plane of a bridge, further information about
> which can be obtained based on dp->bridge_dev and dp->bridge_num.
> It can then compose a DSA tag for injecting a data plane packet into
> that bridge number.
> 
> For the switch driver side, we offer two new dsa_switch_ops methods,
> called .port_bridge_fwd_offload_{add,del}, which are modeled after
> .port_bridge_{join,leave}.
> These methods are provided in case the driver needs to configure the
> hardware to treat packets coming from that bridge software interface as
> data plane packets. The switchdev <-> bridge interaction happens during
> the netdev_master_upper_dev_link() call, so to switch drivers, the
> effect is that the .port_bridge_fwd_offload_add() method is called
> immediately after .port_bridge_join().
> 
> If the bridge number exceeds the number of bridges for which the switch
> driver can offload the TX data plane (and this includes the case where
> the driver can offload none), DSA falls back to simply returning
> tx_fwd_offload = false in the switchdev_bridge_port_offload() call.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---

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