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Compared to other DSA switches, in the Ocelot cores, the RX filtering is a much more important concern. Firstly, the primary use case for Ocelot is non-DSA, so there isn't any secondary Ethernet MAC [the DSA master's one] to implicitly drop frames having a DMAC we are not interested in. So the switch driver itself needs to install FDB entries towards the CPU port module (PGID_CPU) for the MAC address of each switch port, in each VLAN installed on the port. Every address that is not whitelisted is implicitly dropped. This is in order to achieve a behavior similar to N standalone net devices. Secondly, even in the secondary use case of DSA, such as illustrated by Felix with the NPI port mode, that secondary Ethernet MAC is present, but its RX filter is bypassed. This is because the DSA tags themselves are placed before Ethernet, so the DMAC that the switch ports see is not seen by the DSA master too (since it's shifter to the right). So RX filtering is pretty important. A good RX filter won't bother the CPU in case the switch port receives a frame that it's not interested in, and there exists no other line of defense. Ocelot is pretty strict when it comes to RX filtering: non-IP multicast and broadcast traffic is allowed to go to the CPU port module, but unknown unicast isn't. This means that traffic reception for any other MAC addresses than the ones configured on each switch port net device won't work. This includes use cases such as macvlan or bridging with a non-Ocelot (so-called "foreign") interface. But this seems to be fine for the scenarios that the Linux system embedded inside an Ocelot switch is intended for - it is simply not interested in unknown unicast traffic, as explained in Allan Nielsen's presentation [0]. On the other hand, the Felix DSA switch is integrated in more general-purpose Linux systems, so it can't afford to drop that sort of traffic in hardware, even if it will end up doing so later, in software. Actually, unknown unicast means more for Felix than it does for Ocelot. Felix doesn't attempt to perform the whitelisting of switch port MAC addresses towards PGID_CPU at all, mainly because it is too complicated to be feasible: while the MAC addresses are unique in Ocelot, by default in DSA all ports are equal and inherited from the DSA master. This adds into account the question of reference counting MAC addresses (delayed ocelot_mact_forget), not to mention reference counting for the VLAN IDs that those MAC addresses are installed in. This reference counting should be done in the DSA core, and the fact that it wasn't needed so far is due to the fact that the other DSA switches don't have the DSA tag placed before Ethernet, so the DSA master is able to whitelist the MAC addresses in hardware. So this means that even regular traffic termination on a Felix switch port happens through flooding (because neither Felix nor Ocelot learn source MAC addresses from CPU-injected frames). So far we've explained that whitelisting towards PGID_CPU: - helps to reduce the likelihood of spamming the CPU with frames it won't process very far anyway - is implemented in the ocelot driver - is sufficient for the ocelot use cases - is not feasible in DSA - breaks use cases in DSA, in the current status (whitelisting enabled but no MAC address whitelisted) So the proposed patch allows unknown unicast frames to be sent to the CPU port module. This is done for the Felix DSA driver only, as Ocelot seems to be happy without it. [0]: https://www.youtube.com/watch?v=B1HhxEcU7Jg Suggested-by: Allan W. Nielsen <allan.nielsen@microchip.com> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Reviewed-by: Allan W. Nielsen <allan.nielsen@microchip.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.