On 09/06/2017 09:42 AM, Andrew Lunn wrote:

quoted

quoted

On the switch asics we work with, the driver has information if the
packet was
forwarded in hardware. This is per packet reason code telling why the
CPU is seeing the packet.
The driver can use this information to reset skb->offload_fwd_mark to
allow software forward.

quoted

I am not positive this is universally available across different
switch vendors.

It is not universally available. We cannot rely on it being available
with switches supported by DSA.

We have a few choices:

1) We assume anything the switch forwards to the CPU has also been
   sent out whatever ports of the switch it needs to. Set
   offload_fwd_mark.

2) We assume anything the switch forwards to the CPU has not gone
   anywhere else, and the bridge needs to send it out whatever ports
   it thinks. Don't set offload_fwd_mark.

3) We define some rules about what packets the switch should handle,
   and then do some deep packet inspection to decide if
   offload_fwd_mark should be set or not.

I don't see 3) being possible. We are dealing with a fixed silicon
data path, not something which is fully programmable.

So it is down to 1) or 2). I've been assuming 1), but maybe we need to
discuss that as well.

At the very least we should probably move the skb->offload_fwd_mark
setting down into the individual taggers since they should be in a
better position to set it or not based on the switch device they are
driving, this should address, on a per-switch basis whether 2) or 3)
applies to a given switch.

That being said, I have a feeling that the Marvell switches behave a
tiny bit differently than others in that they do not flood broadcast by
default in a given L2 domain.

On b53/bcm_sf2 there is the ability to disable the reception of
broadcast frames on the management/CPU port, and while there is the
ability to configure which ports should be flooded in case of
unicast/multicast lookup failures, I don't see anything for Broadcast,
so I am assuming this will get forwarded by default. Will test with your
patch set later on time permitting.
-- 
Florian