Re: [PATCH net-next] net: mscc: ocelot: Workaround to allow traffic to CPU in standalone mode

Hi,

On 19.02.2020 16:05, Vladimir Oltean wrote:

On Wed, 19 Feb 2020 at 12:17, Allan W. Nielsen
[off-list ref] wrote:

quoted

With Ocelot we do not see this spamming - and I still do not understand
why this is seen with Felix.

I should have watched my words.
When doing what all the other DSA switches do, which is enabling a
bulk forwarding path between the front-panel ports and the CPU, the
Ocelot switch core is more susceptible to doing more software
processing work than other devices in its class, for the same end
effect of dropping packets that the CPU is not interested in (say an
unknown unicast MAC that is not present in the switch FDB nor in the
DSA master's RX filter). In such a scenario, any other DSA system
would have the host port drop these packets in hardware, by virtue of
the unknown unicast MAC not being being present RX filter. With
Ocelot, this mechanism that prevents software work being done for
dropping is subverted. So to avoid this design limitation, the Ocelot
core does not enable a bulk forwarding path between the front-panel
ports and the CPU.

Hope this is clearer.

Horatiu and I have looked further into this, done a few experiments, and
discussed with the HW engineers who have a more detailed version of how
the chips are working and how Ocelot and Felix differs.

Here are our findings:

- The most significant bit in the PGID table is "special" as it is a
   CPU-copy bit.
- This bit is not being used in the source filtering! This means that
   your original patch can be applied without breaking Ocelot (the
   uninitialized cpu field must be fixed though).
   - Still I do not think we should do this as it is not the root-casuse
- In Felix we have 2 ways to get frames to the CPU, in Ocelot we have 1
   (Ocelot also has two if it uses an NPI port, but it does not do that
   in the current driver).
   - In Felix you can get frames to the CPU by either using the CPU port
     (port 6), or by using the NPI port (which can be any in the range of
     0-5).
     - But you should only use the CPU port, and not the NPI port
       directly. Using the NPI port directly will cause the two targets
       to behave differently, and this is not what we do when testing all
       the use-cases on the switch.
   - In Ocelot you can only get frames to the CPU by using the CPU port
     (port 11).

Due to this, I very much think you need to fix this, such that Felix
always port 6 to reach the CPU (with the exception of writing
QSYS_EXT_CPU_CFG where you "connect" the CPU queue/port to the NPI
port).

If you do this change, then the Ocelot and Felix should start to work in
the same way.

Then, if you want the CPU to be part of the unicast flooding (this is
where this discussion started), then you should add the CPU port to the
PGID entry pointed at in ANA:ANA:FLOODING:FLD_UNICAST. This should be
done for Felix and not for Ocelot.

If you want the analyser (where the MAC table sits), to "learn" the CPU
MAC (which is needed if you do not want to have the CPU mac as a static
entry in the MAC-table), then you need to set the 'src-port' to 6 (if it
is Ocelot then it will be 11) in the IFH:

anielsen@lx-anielsen ~ $ ef hex ifh-oc1 help
ifh-oc1          Injection Frame Header for Ocelot1

Specify the ifh-oc1 header by using one or more of the following fields:
- Name ------------ offset:width --- Description --------------------------
   bypass              +  0:  1  Skip analyzer processing
   b1-rew-mac          +  1:  1  Replace SMAC address
   b1-rew-op           +  2:  9  Rewriter operation command
   b0-masq             +  1:  1  Enable masquerading
   b0-masq-port        +  2:  4  Masquerading port
   rew-val             + 11: 32  Receive time stamp
   res1                + 43: 17  Reserved
   dest                + 60: 12  Destination set for the frame. Dest[11] is the CPU
   res2                + 72:  9  Reserved
   src-port            + 81:  4  The port number where the frame was injected (0-12)  <------------------- THIS FIELD
   res3                + 85:  2  Reserved
   trfm-timer          + 87:  4  Timer for periodic transmissions (1..8). If zero then normal injection
   res4                + 91:  6  Reserved
   dp                  + 97:  1  Drop precedence level after policing
   pop-cnt             + 98:  2  Number of VLAN tags that must be popped
   cpuq                +100:  8  CPU extraction queue mask
   qos-class           +108:  3  Classified QoS class
   tag-type            +111:  1  Tag information's associated Tag Protocol Identifier (TPID)
   pcp                 +112:  3  Classified PCP
   dei                 +115:  1  Classified DEI
   vid                 +116: 12  Classified VID


/Allan