netdev - [PATCH net-next 0/3] net: dsa: Allow default tag protocol to be overridden from DT

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Date:   Fri, 26 Mar 2021 11:56:45 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     andrew@...n.ch, vivien.didelot@...il.com, f.fainelli@...il.com,
        olteanv@...il.com, netdev@...r.kernel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org
Subject: [PATCH net-next 0/3] net: dsa: Allow default tag protocol to be overridden from DT

This is logically the v2 of this patch:
https://lore.kernel.org/netdev/20210323102326.3677940-1-tobias@waldekranz.com/

In addition to the mv88e6xxx support to dynamically change the
protocol, it is now possible to override the protocol from the device
tree. This means that when a board vendor finds an incompatibility,
they can specify a working protocol in the DT, and users will not have
to worry about it.

Some background information:

In a system using an NXP T1023 SoC connected to a 6390X switch, we
noticed that TO_CPU frames where not reaching the CPU. This only
happened on hardware port 8. Looking at the DSA master interface
(dpaa-ethernet) we could see that an Rx error counter was bumped at
the same rate. The logs indicated a parser error.

It just so happens that a TO_CPU coming in on device 0, port 8, will
result in the first two bytes of the DSA tag being one of:

00 40
00 44
00 46

My guess was that since these values looked like 802.3 length fields,
the controller's parser would signal an error if the frame length did
not match what was in the header.

This was later confirmed using two different workarounds provided by
Vladimir. Unfortunately these either bypass or ignore the hardware
parser and thus robs working combinations of the ability to do RSS and
other nifty things. It was therefore decided to go with the option of
a DT override.

Tobias Waldekranz (3):
  net: dsa: mv88e6xxx: Allow dynamic reconfiguration of tag protocol
  net: dsa: Allow default tag protocol to be overridden from DT
  dt-bindings: net: dsa: Document dsa,tag-protocol property

 .../devicetree/bindings/net/dsa/dsa.yaml      |  7 ++
 drivers/net/dsa/mv88e6xxx/chip.c              | 41 +++++++-
 drivers/net/dsa/mv88e6xxx/chip.h              |  3 +
 include/net/dsa.h                             |  5 +
 net/dsa/dsa2.c                                | 95 +++++++++++++++----
 5 files changed, 132 insertions(+), 19 deletions(-)

-- 
2.25.1