net: dsa: tag_ks8995: Add the KS8995 tag handling

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The KS8995 100Mbit switch can do proper DSA per-port tagging
with the proper set-up. This adds the code to handle ingress
and egress KS8995 tags.

The tagger is used by the KSZ8995XA support added later in this
series.

The tag is a modified 0x8100 ethertype tag where a bit in the
last nibble is set for each target port.

Always insert a distinct outer switch tag. User ports remove this
field on egress, so reusing an existing 802.1Q header would consume
the sender VLAN tag instead of preserving it.

Push any hardware-accelerated VLAN tag into the packet first. This
keeps the switch tag at offset 12 while retaining 802.1Q, 802.1ad and
stacked VLAN headers as inner payload, and avoids relying on a valid
SKB MAC header in direct transmit paths.

Rate-limit receive untagging errors so repeated failures cannot flood
the kernel log.

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Signed-off-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260916-ks8995-to-ksz8-v15-2-8825ff5fd4be@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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This commit is contained in:

Linus Walleij 2026-09-16 12:20:59 +02:00 • committed by Jakub Kicinski

parent 7a5e75f649

commit ca30cd47fe

5 changed files with 190 additions and 0 deletions

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1

MAINTAINERS

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include/net/dsa.h

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net/dsa/Kconfig

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net/dsa/Makefile

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net/dsa/tag_ks8995.c

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