linux-kernel - Re: [PATCH net v2] net: dsa: tag_rtl4

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Date:   Tue, 31 Oct 2023 18:34:39 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net: dsa: tag_rtl4_a: Bump min packet size

On Tue, Oct 31, 2023 at 03:16:50PM +0100, Linus Walleij wrote:
> On Tue, Oct 31, 2023 at 12:33 AM Vladimir Oltean <olteanv@...il.com> wrote:
> > On Mon, Oct 30, 2023 at 11:57:33PM +0100, Linus Walleij wrote:
> > > Here you can incidentally also see what happens if we don't pad the big packets:
> > > the packet gets truncated.
> >
> > Are we sure we are debugging a switch problem? On how many platforms
> > with the RTL8366RB can the issue be seen? Is the conduit interface the
> > same on all these platforms, or is it different and that makes no
> > difference?
> 
> I don't have any other RTL8366RB systems than the D-Link DIR-685.
> 
> I however have several systems with the same backing ethernet controller
> connected directly to a PHY and they all work fine.
> 
> Yours,
> Linus Walleij

Ok, so we don't have a confirmation of breakage with other conduit
interface than the Gemini driver, either. So a problem there is still
not off the table.

So on the gemini-dlink-dir-685.dts platform, you can also use &gmac1 as
a plain Ethernet port, right?

If possible, could you set up dsa_loop (enable CONFIG_NET_DSA_LOOP, replace
"eth0" in dsa_loop_pdata with the netdev name of &gmac1, replace DSA_TAG_PROTO_NONE
in dsa_loop_get_protocol() with your tagging protocol) and put a tcpdump
on the remote end of the gmac1 port, to see if the issue isn't, in fact,
somewhere else, maybe gmac_start_xmit()?

With dsa_loop, you turn &gmac1 into a conduit interface of sorts, except
for the fact that there is no switch to process the DSA-tagged packets,
you see those packets on the remote end, and you can investigate there
whether it's the switch who's corrupting/truncating, or if they're
somehow sent corrupted/truncated by Gemini on the wire (which would not
be visible in a local tcpdump).