netdev - Re: [PATCH net-next v4 11/11] net: dsa: realtek: rtl8365mb: multiple cpu ports, non cpu extint

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Message-ID: <87fspll5ba.fsf@bang-olufsen.dk>
Date:   Tue, 18 Jan 2022 10:13:46 +0000
From:   Alvin Šipraga <ALSI@...g-olufsen.dk>
To:     Luiz Angelo Daros de Luca <luizluca@...il.com>
CC:     Frank Wunderlich <frank-w@...lic-files.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "olteanv@...il.com" <olteanv@...il.com>,
        "arinc.unal@...nc9.com" <arinc.unal@...nc9.com>
Subject: Re: [PATCH net-next v4 11/11] net: dsa: realtek: rtl8365mb: multiple
 cpu ports, non cpu extint

Luiz Angelo Daros de Luca <luizluca@...il.com> writes:

>> the problem is checksum offloading on the gmac (soc-side)
>
> I suggested it might be checksum problem because I'm also affected. In
> my case, I have an mt7620a SoC connected to the rtl8367s switch. The
> OS offloads checksum to HW but the mt7620a cannot calculate the
> checksum with the (EtherType) Realtek CPU Tag in place. I'll try to
> move the CPU tag to test if the mt7620a will then digest the frame
> correctly.

You have two choices:

    enum rtl8365mb_cpu_position {
            RTL8365MB_CPU_POS_AFTER_SA = 0,
            RTL8365MB_CPU_POS_BEFORE_CRC = 1,
    };

I hardcoded it to AFTER_SA but if you find that this solves the problem
for some MACs then it might be worth adding a device tree property for
this to make it configurable. Of course remember to keep it
backward-compatible, and add a note to future travellers in the bindings
that this might solve checksum errors :-)

Kind regards,
Alvin