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

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Date:   Tue, 11 Dec 2018 16:02:00 +1100
From:   NeilBrown <neil@...wn.name>
To:     Bjørn Mork <bjorn@...k.no>, 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,
        René van Dorst <opensource@...rst.com>
Subject: Re: [PATCH 0/3]: net: dsa: mt7530: support MT7530 in the MT7621 SoC

On Fri, Nov 30 2018, Bjørn Mork wrote:

> 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.

Thanks a lot for posting this.  I'd be very happy to see the staging
driver disappear once this is ready and in mainline.

I got your patch working on 4.20-rc5 and did a performance comparison.
With the staging driver (using iperf3) I get
  220 MBit/sec in
  680 MBit/sec out

with the patched mainline driver I get
  190 MBit/sec in
   93 MBit/sec out

(numbers are a bit rubbery, but within 10%)

I haven't looked into why this might be, but thought I would mention it.

Strangely when I test with scp, I get about 10MB/sec in both directions
with both drivers.  Maybe the CPU limits encryption speed.

I have a 4.4-based kernel where I get 940MBit/sec both ways - using a
precursor of the current staging driver.

Thanks,
NeilBrown


>
>> 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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