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    SubjectRe: [RFC PATCH net-next 3/3] net: dsa: listen for SWITCHDEV_{FDB,DEL}_ADD_TO_DEVICE on foreign bridge neighbors
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    On 11/9/2020 4:38 AM, Vladimir Oltean wrote:
    > On Mon, Nov 09, 2020 at 02:31:11PM +0200, Vladimir Oltean wrote:
    >> I need to sit on this for a while. How many DSA drivers do we have that
    >> don't do SA learning in hardware for CPU-injected packets? ocelot/felix
    >> and mv88e6xxx? Who else? Because if there aren't that many (or any at
    >> all except for these two), then I could try to spend some time and see
    >> how Felix behaves when I send FORWARD frames to it. Then we could go on
    >> full blast with the other alternative, to force-enable address learning
    >> from the CPU port, and declare this one as too complicated and not worth
    >> the effort.
    >
    > In fact I'm not sure that I should be expecting an answer to this
    > question. We can evaluate the other alternative in parallel. Would you
    > be so kind to send some sort of RFC for your TX-side offload_fwd_mark so
    > that I could test with the hardware I have, and get a better understanding
    > of the limitations there?

    For Broadcom switches, ARL (Address Resolution Logic, where learning
    happens) is bypassed when packets ingress the CPU port with opcode 1
    which is what net/dsa/tag_brcm.c uses. When opcode 0 is used, address
    learning occurs.

    The reason why opcode 1 is used is because of the Advanced Congestion
    Buffering (ACB) which requires us to steer packets towards a particular
    switch port and egress queue number within that port. With opcode 0 we
    would not be able to do that.

    We could make the opcode dependent on the switch/DSA master since not
    all combinations support ACB, but given we have 3 or 4 Ethernet switches
    kind within DSA that do not do learning from the CPU port, I guess we
    need a solution to that problem somehow.
    --
    Florian

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