Re: [PATCH v3 net-next 04/15] net: dsa: felix: add new VLAN-based tagger

On Mon, Jan 18, 2021 at 06:17:20PM +0200, Vladimir Oltean wrote:

From: Vladimir Oltean <vladimir.oltean@nxp.com>

There are use cases for which the existing tagger, based on the NPI
(Node Processor Interface) functionality, is insufficient.

Namely:
- Frames injected through the NPI port bypass the frame analyzer, so no
  source address learning is performed, no TSN stream classification,
  etc.
- Flow control is not functional over an NPI port (PAUSE frames are
  encapsulated in the same Extraction Frame Header as all other frames)
- There can be at most one NPI port configured for an Ocelot switch. But
  in NXP LS1028A and T1040 there are two Ethernet CPU ports. The non-NPI
  port is currently either disabled, or operated as a plain user port
  (albeit an internally-facing one). Having the ability to configure the
  two CPU ports symmetrically could pave the way for e.g. creating a LAG
  between them, to increase bandwidth seamlessly for the system.

So, there is a desire to have an alternative to the NPI mode.

This patch brings an implementation of the software-defined tag_8021q.c
tagger format, which also preserves full functionality under a
vlan_filtering bridge (unlike sja1105, the only other user of
tag_8021q).

It does this by using the TCAM engines for:
- pushing the RX VLAN as a second, outer tag, on egress towards the CPU
  port
- redirecting towards the correct front port based on TX VLAN and
  popping that on egress

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---

Should both taggers be reported as DSA_TAG_PROTO_OCELOT as I am doing in
the current patchset? Currently a kernel can only be built with one
tagger or the other. But it is not possible to e.g. rmmod one tagger and
insmod another one.

If we allow compilation of more than one tagger for the same hardware,
how do we select between them if both are built into the same kernel?