Date:   Fri, 30 Nov 2018 13:16:33 +0100
From:   Bjørn Mork <bjorn@...k.no>
To:     gerg@...nel.org
Cc:     sean.wang@...iatek.com, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        netdev@...r.kernel.org, blogic@...nwrt.org, neil@...wn.name,
        René van Dorst <opensource@...rst.com>
Subject: Re: [PATCH 0/3]: net: dsa: mt7530: support MT7530 in the MT7621 SoC

gerg@...nel.org writes:

> 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.

Great!  Good to see someone pushing this idea forward.

> 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.

No offense, but the mt7621-eth driver in staging is horrible.  What both
René and I have had some success with is adapting the mtk_eth_soc driver
already in drivers/net/ethernet/mediatek/.  Yes, I know this is supposed
to be for other SoCs, but the basic design is obviously the same.

I have had some success with a first hackish attemt based on OpenWrt.
You can find the early tree here, but note that my focus was basically
getting one specific MT7621 board up and running:
https://github.com/bmork/LEDE/tree/mt7621-with-mainline-eth-driver

This patch has most of the necessary changes to enable that driver for
MT7621:
https://github.com/bmork/LEDE/commit/3293bc63f5461ca1eb0bbc4ed90145335e7e3404

Not a big deal, as you can see.  There is of course a reason I didn't
submit this here yet: It is by no means finished...  But it works. And I
have both GMACs working with this driver, which was my primary goal.

> 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.

Hmm.  How do I test this?

> 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.

Are you referring to the configured MTU size or some other maximal size?
If MTU, then I don't seem to have this issue with the driver from
drivers/net/ethernet/mediatek/.



Bjørn

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