Re: [PATCH v2 14/14] net: ethernet: mtk_eth_soc: support creating mac address based offload entries

[Felix Fietkau]

On 11.04.22 15:00, Andrew Lunn wrote:
> On Thu, Apr 07, 2022 at 08:21:43PM +0200, Felix Fietkau wrote:
> > On 07.04.22 20:10, Andrew Lunn wrote:
> > > On Tue, Apr 05, 2022 at 09:57:55PM +0200, Felix Fietkau wrote:
> > > > This will be used to implement a limited form of bridge offloading.
> > > > Since the hardware does not support flow table entries with just source
> > > > and destination MAC address, the driver has to emulate it.
> > > > 
> > > > The hardware automatically creates entries entries for incoming flows, even
> > > > when they are bridged instead of routed, and reports when packets for these
> > > > flows have reached the minimum PPS rate for offloading.
> > > > 
> > > > After this happens, we look up the L2 flow offload entry based on the MAC
> > > > header and fill in the output routing information in the flow table.
> > > > The dynamically created per-flow entries are automatically removed when
> > > > either the hardware flowtable entry expires, is replaced, or if the offload
> > > > rule they belong to is removed
> > > 
> > > > +
> > > > +	if (found)
> > > > +		goto out;
> > > > +
> > > > +	eh = eth_hdr(skb);
> > > > +	ether_addr_copy(key.dest_mac, eh->h_dest);
> > > > +	ether_addr_copy(key.src_mac, eh->h_source);
> > > > +	tag = skb->data - 2;
> > > > +	key.vlan = 0;
> > > > +	switch (skb->protocol) {
> > > > +#if IS_ENABLED(CONFIG_NET_DSA)
> > > > +	case htons(ETH_P_XDSA):
> > > > +		if (!netdev_uses_dsa(skb->dev) ||
> > > > +		    skb->dev->dsa_ptr->tag_ops->proto != DSA_TAG_PROTO_MTK)
> > > > +			goto out;
> > > > +
> > > > +		tag += 4;
> > > > +		if (get_unaligned_be16(tag) != ETH_P_8021Q)
> > > > +			break;
> > > > +
> > > > +		fallthrough;
> > > > +#endif
> > > > +	case htons(ETH_P_8021Q):
> > > > +		key.vlan = get_unaligned_be16(tag + 2) & VLAN_VID_MASK;
> > > > +		break;
> > > > +	default:
> > > > +		break;
> > > > +	}
> > > 
> > > I'm trying to understand the architecture here.
> > > 
> > > We have an Ethernet interface and a Wireless interface. The slow path
> > > is that frames ingress from one of these interfaces, Linux decides
> > > what to do with them, either L2 or L3, and they then egress probably
> > > out the other interface.
> > > 
> > > The hardware will look at the frames and try to spot flows? It will
> > > then report any it finds. You can then add an offload, telling it for
> > > a flow it needs to perform L2 or L3 processing, and egress out a
> > > specific port? Linux then no longer sees the frame, the hardware
> > > handles it, until the flow times out?
> > Yes, the hw handles it until either the flow times out, or the corresponding
> > offload entry is removed.
> >
> > For OpenWrt I also wrote a daemon that uses tc classifier BPF to accelerate
> > the software bridge and create hardware offload entries as well via hardware
> > TC flower rules: https://github.com/nbd168/bridger
> > It works in combination with these changes.
>
> What about the bridge? In Linux, it is the software bridge which
> controls all this at L2, and it should be offloading the flows, via
> switchdev. The egress port you derive here is from the software bridge
> FDB?
My code uses netlink to fetch and monitor the bridge configuration, 
including fdb, port state, vlans, etc. and it uses that for the offload 
path - no extra configuration needed.

> > > So i'm wondering what is going on here. So is this a frame which has
> > > ingressed, either from the WiFi, or another switch port, gone to the
> > > software bridge, bridges to a DSA slave interface, the DSA tagger has
> > > added a tag and now it is in the master interface? Can you accelerate
> > > such frames? What is adding the DSA tag on the fast path? And in the
> > > opposite direction, frames which egress the switch which have a DSA
> > > tag and are heading to the WiFi, what is removing the tag? Does the
> > > accelerator also understand the tag and know what to do with it?WiFi ->
> > > Ethernet is not supported by MT7622, but will be added for newer
>
> > SoCs like MT7986. The PPE supports both parsing and inserting MT7530
> > compatible DSA tags. For Ethernet->WiFi flows, the PPE will also add
> > required metadata that is parsed by the MT7915 WiFi Firmware in order to
> > figure out what vif/station the packets were meant for.
>
> O.K. What about IGMP and multicast? Does the accelerate match on IGMP
> and forwards it to the CPU, rather than follow the flow rules? Can you
> set multiple egress destinations for multicast so that it can go both
> to the switch and the host, when the host has a local interest in the
> traffic?
IGMP/multicast isn't handled yet at the moment. I still need to do some 
research on what can be offloaded and how. The offload only handles 
unicast and everything else is going through the CPU.

- Felix