netdev - [PATCH 0/3]: net: dsa: mt7530: support MT7530 in the MT7621 SoC

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Message-Id: <20181130075737.8041-1-gerg@kernel.org>
Date:   Fri, 30 Nov 2018 17:57:34 +1000
From:   gerg@...nel.org
To:     sean.wang@...iatek.com, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        netdev@...r.kernel.org
Cc:     blogic@...nwrt.org, neil@...wn.name
Subject: [PATCH 0/3]: net: dsa: mt7530: support MT7530 in the MT7621 SoC

I have been working towards supporting the MT7530 switch as used in the
MediaTek MT7621 SoC. Unlike the MediaTek MT7623 the MT7621 is built around
a dual core MIPS CPU architecture. But underneath it is what appears to
be the same 7530 switch.

The following 3 patches are more of an RFC than anything. They allow
use of the mt7530 dsa driver on this device - though with some issues
still to resolve. The primary change required is to not use the 7623
specific clock and regulator setup - none of that applies when using
the 7621 (and maybe other devices?). The other change required is to
set the 7530 MFC register CPU port number and enable bit.

The unresolved issues I still have appear to be more related to the
MT7621 ethernet driver (drivers/staging/mt7621-eth/*). I am hoping
someone might have some ideas on these. I don't really have any good
documentation on the ethernet devices on the 7621, so I am kind of
working in the dark here.

1. TX packets are not getting an IP header checksum via the normal
   off-loaded checksumming when in DSA mode. I have to switch off
   NETIF_F_IP_CSUM, so the software stack generates the checksum.
   That checksum offloading works ok when not using the 7530 DSA driver.

2. Maximal sized RX packets get silently dropped. So receive side packets
   that are large (perfect case is the all-but-last packets in a fragemented
   larger packet) appear to be dropped at the mt7621 ethernet MAC level.
   The 7530 MIB switch register counters show receive packets at the physical
   switch port side and at the CPU switch port - but I get no packets
   received or errors in the 7621 ethernet MAC. If I set the mtu of the
   server at the other end a little smaller (a few bytes is enough) then
   I get all the packets through. It seems like the DSA/VLAN tag bytes
   are causing a too large packet to get silently dropped somewhere.

Any thoughts greatly appreciated...

 Documentation/devicetree/bindings/net/dsa/mt7530.txt |    5 +
 drivers/net/dsa/mt7530.c                             |   95 ++++++++++++-------
 drivers/net/dsa/mt7530.h                             |    5 +
 3 files changed, 70 insertions(+), 35 deletions(-)