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Date: Thu, 7 May 2020 20:32:32 -0700 From: Florian Fainelli <f.fainelli@...il.com> To: Vladimir Oltean <olteanv@...il.com>, andrew@...n.ch, vivien.didelot@...il.com, davem@...emloft.net Cc: jiri@...nulli.us, idosch@...sch.org, kuba@...nel.org, netdev@...r.kernel.org, nikolay@...ulusnetworks.com, roopa@...ulusnetworks.com, mingkai.hu@....com Subject: Re: [PATCH v3 net-next 4/4] net: dsa: sja1105: implement cross-chip bridging operations On 5/3/2020 3:12 PM, Vladimir Oltean wrote: > From: Vladimir Oltean <vladimir.oltean@....com> > > sja1105 uses dsa_8021q for DSA tagging, a format which is VLAN at heart > and which is compatible with cascading. A complete description of this > tagging format is in net/dsa/tag_8021q.c, but a quick summary is that > each external-facing port tags incoming frames with a unique pvid, and > this special VLAN is transmitted as tagged towards the inside of the > system, and as untagged towards the exterior. The tag encodes the switch > id and the source port index. > > This means that cross-chip bridging for dsa_8021q only entails adding > the dsa_8021q pvids of one switch to the RX filter of the other > switches. Everything else falls naturally into place, as long as the > bottom-end of ports (the leaves in the tree) is comprised exclusively of > dsa_8021q-compatible (i.e. sja1105 switches). Otherwise, there would be > a chance that a front-panel switch transmits a packet tagged with a > dsa_8021q header, header which it wouldn't be able to remove, and which > would hence "leak" out. > > The only use case I tested (due to lack of board availability) was when > the sja1105 switches are part of disjoint trees (however, this doesn't > change the fact that multiple sja1105 switches still need unique switch > identifiers in such a system). But in principle, even "true" single-tree > setups (with DSA links) should work just as fine, except for a small > change which I can't test: dsa_towards_port should be used instead of > dsa_upstream_port (I made the assumption that the routing port that any > sja1105 should use towards its neighbours is the CPU port. That might > not hold true in other setups). > > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com> Reviewed-by: Florian Fainelli <f.fainelli@...il.com> -- Florian
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