Merge branch 'introduce-the-dsa_xmit_port_mask-tagging-protocol-helper'

Vladimir Oltean says:

====================
Introduce the dsa_xmit_port_mask() tagging protocol helper

What
----

Some DSA tags have just the port number in the TX header format, others
have a bit field where in theory, multiple bits can be set, even though
DSA only sets one.

The latter kind is now making use of a dsa_xmit_port_mask() helper,
which will decide when to set more than 1 bit in that mask.

Why
---

David Yang has pointed out in a recently posted patch that HSR packet
duplication on transmission can be offloaded even on HSR-unaware
switches. This should be made generally available to all DSA switches.

How to test
-----------

These patches just lay the groundwork, and there should be no functional
change - so for this set, regression testing is all that's necessary.

For testing the HSR packet duplication idea, I've put together a branch:
https://github.com/vladimiroltean/linux/commits/dsa-simple-hsr-offload/
where most drivers are patched to call dsa_port_simple_hsr_join() and
dsa_port_simple_hsr_leave().

Assuming there are volunteers to also test the latter, one can enable
CONFIG_HSR and create a HSR device using:
$ ip link add name hsr0 type hsr slave1 swp0 slave2 swp1 supervision 45 version 1

This needs to be connected using 2 cables to another system where the
same command was run. Then, one should be able to ping the other board
through the hsr0 interface.

Without the Github branch, a ping over HSR should increase the DSA
conduit interface's TX counters by 2 packets. With the Github branch,
the TX counters should increase by only 1 packet.

Why so many patches
-------------------

To avoid the situation where a patch has to be backported, conflicts
with the work done here, pulls this in as a dependency, and that pulls
in 13 other unrelated drivers. These don't have any dependencies between
each other and can be cherry-picked at will (except they all depend on
patch 1/15).
====================

Link: https://patch.msgid.link/20251127120902.292555-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>