Date:   Thu, 4 Aug 2022 00:02:31 +0200
From:   Hauke Mehrtens <hauke@...ke-m.de>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Vladimir Oltean <olteanv@...il.com>
Cc:     netdev@...r.kernel.org, andrew@...n.ch, vivien.didelot@...il.com,
        f.fainelli@...il.com, Aleksander Jan Bajkowski <olek2@...pl>
Subject: Re: net: dsa: lantiq_gswip: getting the first selftests to pass

On 7/31/22 22:49, Martin Blumenstingl wrote:
> Hi Vladimir,
> 
> On Fri, Jul 29, 2022 at 2:05 AM Vladimir Oltean <olteanv@...il.com> wrote:
> [...]
>>> - disable learning on all ports
>>
>> Yes, here's just one other example of what can go wrong if it's enabled
>> on standalone ports, if you need to see it:
>> https://lore.kernel.org/netdev/20220727233249.fpn7gyivnkdg5uhe@skbuf/T/#m2e27a5385f70ee3440ee7f6250aaafdbfdc7446b
>>
>> Essentially every time when there's a chance that the switch will
>> receive on one port what another port has sent, learning will be a
>> problem. This is why it's also problematic for the selftests - because
>> we intentionally put 2 pairs of ports in loopback.
> Makes sense, thanks!
> 
>>> - disable unicast flooding on all ports
>>
>> I am having trouble saying 'yes' or 'no' to this because I don't know
>> exactly what you mean. By flooding a packet, I understand "if its MAC DA
>> is unknown to the FDB, deliver it to this set of ports". But flooding,
>> like learning, is essentially a bridging service concept, so it applies
>> only to packets coming from a particular bridging domain. In the case of
>> a standalone port, packets come only from the CPU, via the control
>> plane. Depending how the hardware is constructed, when you inject a
>> packet to a port, maybe there won't be any ifs or buts and the switch
>> will just deliver it there (I call this behavior: "control packets
>> bypass FDB lookup", or "CPU is in god mode"). So maybe it doesn't matter
>> whether unicast flooding is enabled on all standalone ports or not, as
>> long as the macroscopically expected behavior can be observed: if
>> software xmits a packet to a port, the packet gets delivered regardless
>> of MAC DA.
> I think I do understand it now.
> We want the defaults to apply to standalone ports. Since flooding does
> not exist there we should disable it (for both, unicast and
> broadcast/multicast traffic). When flooding is wanted on a specific
> port it'll be enabled through port_bridge_flags.
> 
> [...]
>>> - (GSWIP can only enable broadcast and multicast at the same time, so
>>> that's enabled too)
>>
>> I think the GSWIP would not be the only one in that category. The
>> mv88e6xxx driver puts the ff:ff:ff:ff:ff:ff address in the FDB and that
>> controls broadcast flooding, while the single knob that you mention
>> controls what's left - i.e. multicast.
> 
>>> I think skb->offload_fwd_mark needs to be set unless we know that the
>>> hardware wasn't able to forward the frame/packet.
>>> In the vendor sources I was able to find the whole RX tag structure: [0]
>>> I am not sure about the "mirror" bit (I assume this is: packet was
>>> received on this port because this port is configured as a mirroring
>>> target). All other bits seem irrelevant for skb->offload_fwd_mark -
>>> meaning we always have to set skb->offload_fwd_mark.
>>>
>>> I have lots of failures in bridge_vlan_aware.sh and
>>> bridge_vlan_unaware.sh - even before any of my changes - which I'll
>>> need to investigate.
>>
>> I don't remember the problems I faced while making these tests pass on
>> my hardware, and I also don't think they'll be the same as the ones
>> you'll face.
> I'll postpone bridge_vlan_unaware.sh investigations until I have the
> standalone tests (which are relevant for GSWIP, meaning: excluding the
> multicast ones) from local_termination.sh passing.
> 
> [...]
>>> - the DSA_DB_BRIDGE case is easy as this is basically what we had
>>> implemented before and I "just" need to look up the FID based on
>>> db.bridge.dev
>>
>> Or db.bridge.num (this is currently set to 0 by DSA because you don't
>> declare ds->fdb_isolation = true), whichever is more convenient.
> Using db.bridge.num will probably allow us to get rid of the
> priv->vlans array in the GSWIP driver. For now I'm using the bridge
> dev since "it works" until tests are passing.
> 
> [...]
>>> - DSA_DB_PORT for the CPU port: the port argument for port_fdb_add is
>>> the CPU port - but we can't map this to a FID (those are always tied
>>> to either a bridge or a user port). So instead I need to look at db.dp
>>> and for example use it's index for getting the FID (for standalone
>>> ports the FID is: port index + 1).
>>
>> Looking at db.dp to determine the FID is not a workaround, but rather
>> exactly what you are expected to do.
> Thanks for confirming!
> 
>>> That results in: we're requested to install the CPU ports MAC address
>>> on the CPU port (6),
>>
>> No. The CPU port doesn't have a MAC address (and in fact no port does;
>> it's a switch). But user ports have MAC addresses which are a purely
>> software construct to denote L2 termination. Every user port net device
>> can have its own MAC address, different from the other, and different
>> from the MAC address of the DSA master. Its interpretation is: "if a
>> user port receives a packet with a MAC DA that's equal to the net device's
>> MAC address, send the packet to the CPU, otherwise drop it".
>> It makes the standalone NIC illusion work.
>>
>> The CPU port is just a dumb pipe, it just transports packets to/from our
>> actual user ports. We don't have a termination point for it (or as written
>> in other places: "we don't have a net_device"), so no MAC address, not
>> even as a software construct.
>>
>> A pipe is exactly how you should see the CPU port. It doesn't have a FID
>> (a single port bridge) of its own because it is a part of all FIDs.
>>
>>> but what we actually do is install the FDB entry with the CPU port's
>>> MAC address on a user port (let's say 4, which we get from db.dp).
>>
>> No, quite the other way around.
>>
>> Let's take an example based on what you've described: user port swp4 has
>> MAC address 00:01:02:03:04:05, and CPU port is 6. You'll get a call to
>>
>> port_fdb_add(ds, port = 6, addr = 00:01:02:03:04:05, vid = 0,
>>               db = {type = DSA_DB_PORT, dp = swp4}).
>>
>> What you need to do is create an FDB entry on which only packets
>> received by swp4 in standalone mode will match (so it needs to have a
>> FID equal to the FID that swp4 classifies packets to, in standalone mode),
>> and delivers these packets to the CPU port 6, which is already in that FID,
>> as it is part of every FID. Remember, when swp4 receives a packet and is
>> standalone, it always assigns the FID of that packet to the value that
>> it's configured to (port index + 1, or 5, if you say so). This packet
>> in this FID can either find an entry in the FDB, case in which its
>> destination is certainly the CPU port (that's why port = 6), or the
>> address will be absent from the FDB, case in which the packet will be
>> flooded nowhere (the only other port in this FID, the CPU port, has
>> flooding turned off) => dropped.
>>
>> As mentioned earlier, it's desirable that packets delivered by software,
>> over the CPU port and towards a standalone one, are sent in "god mode",
>> so that the FDB won't be searched at all in that direction.
>>
>> You seem to have something reversed in your terminology, although I
>> can't exactly pinpoint what. When you say "install an FDB entry on port X",
>> what I understand is "make the packets with that FDB entry's MAC DA be
>> delivered towards port X". Or maybe I have something reversed?
>> I'm quite curious to know.
> Thanks a lot for explaining this (yet again)!
> There's three issues with my original sentence:
> - I should have used the term "user port's MAC address" instead of
> "CPU ports MAC"
> - "on the CPU port (6)" needs to be more precise, it should be
> "towards the CPU port (6)"
> - I'm not mentioning the source port (user port) number and thus FID at all
> 
> Also I need to get the idea out of my head that the CPU port is equal to eth0.
> It's not, eth0 is connected to the CPU port on the switch.
> 
> While working on my patches a more practical question came up while I
> was breaking the driver and then trying to make local_termination.sh
> pass again.
> At the start of run_tests for the standalone port scenario I am
> getting the following values:
>    rcv_dmac = 00:01:02:03:04:02
>    MACVLAN_ADDR = 00:00:de:ad:be:ef
> My expectation is that port_fdb_add() is called with these MAC
> addresses. I verified that dsa_switch_supports_uc_filtering() returns
> true, but still I
> 
>>> Now if a packet/frame should target the CPU port we don't need
>>> flooding because the switch knows the destination port based on the
>>> FDB entry we installed.
>>
>> Yes, so rather than the CPU port being a 'dumb' pipe which passes all
>> packets through it, you're making it a slightly 'smarter' pipe which
>> essentially uses the FDB as an RX filter for standalone user ports.
>>
>>> Also I would like to point out that I am still doing all of this in my
>>> spare time.
>>
>> I'm doing this in my spare time as well, and I'm having fun while at it.
>> Sorry for being handwavy and insisting only on explaining the general
>> idea rather than opening the GSWIP manual and checking that what I'm
>> saying is actually implementable. [...]
> I fully understand this and it makes sense as others can also benefit
> from your explanation (since it's generic, not driver specific).
> 
>> I'll do so if you have a specific question about something apparently
>> not mapping to the expectations.
> I still have an issue which I believe is related to the FDB handling.
> 
> I *think* that I have implemented FDB isolation correctly in my
> work-in-progress branch [0].
> 
> The GSWIP140 datasheet (page 82) has a "MAC Learning disable and MAC
> Learning Limitation Description" (table 26).
> In the xRX200 vendor kernel I cannot find the LNDIS bit in
> PCE_PCTRL_3, so I suspect it has only been added in newer GSWIP
> revisions (xRX200 is at least one major IP revision behind GSW140).
> Maybe Hauke knows?
> So what I'm doing to disable learning is setting the "learning limit"
> (which limits the number of entries that can be learned) for that port
> to zero.

There is no LNDIS bit in PCE_PCTRL_3 on the VR9 as far as I know.

What do you want to archive?

If you want to forward the packets only, but not learn the source mac 
address you can configure the PSTATE register inb PCTRL_0 to forwarding 
instead of learning. This is already implemented in 
gswip_port_stp_state_set().
> 
>   My problem is that whenever I disable learning a lot of tests from
> local_termination.sh are failing, including:
> - TEST: lan2: Unicast IPv4 to primary MAC address
> - TEST: lan2: Unicast IPv4 to macvlan MAC address
> 
> Setting the PLIMMOD bit to 1 means that GSWIP won't drop the packet if
> the learning limit is exceeded (the default value seems to be 0).
> This at least works around the first failing test (Unicast IPv4 to
> primary MAC address).
> 
> Based on your understanding of my issue: I am going in the right
> direction when I'm saying that this is an FDB issue?
> 
> 
> Thank you!
> Martin
> 
> 
> [0] https://github.com/xdarklight/linux/commits/lantiq-gswip-integration-20220730

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