From: Felix Fietkau <nbd@nbd.name>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: Sean Wang <sean.wang@mediatek.com>,
Landen Chao <Landen.Chao@mediatek.com>,
DENG Qingfang <dqfext@gmail.com>, Andrew Lunn <andrew@lunn.ch>,
Vivien Didelot <vivien.didelot@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
netdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] net: dsa: tag_mtk: add padding for tx packets
Date: Wed, 11 May 2022 00:06:25 +0200 [thread overview]
Message-ID: <bc4bde22-c2d6-1ded-884a-69465b9d1dc7@nbd.name> (raw)
In-Reply-To: <20220510165233.yahsznxxb5yq6rai@skbuf>
On 10.05.22 18:52, Vladimir Oltean wrote:
> On Tue, May 10, 2022 at 04:52:16PM +0200, Felix Fietkau wrote:
>>
>> On 10.05.22 14:37, Vladimir Oltean wrote:
>> > On Tue, May 10, 2022 at 11:40:13AM +0200, Felix Fietkau wrote:
>> > > Padding for transmitted packets needs to account for the special tag.
>> > > With not enough padding, garbage bytes are inserted by the switch at the
>> > > end of small packets.
>> >
>> > I don't think padding bytes are guaranteed to be zeroes. Aren't they
>> > discarded? What is the issue?
>> With the broken padding, ARP requests are silently discarded on the receiver
>> side in my test. Adding the padding explicitly fixes the issue.
>>
>> - Felix
>
> Ok, I'm not going to complain too much about the patch, but I'm still
> curious where are the so-called "broken" packets discarded.
> I think the receiving MAC should be passing up to software a buffer
> without the extra padding beyond the L2 payload length (at least that's
> the behavior I'm familiar with).
I don't know where exactly these packets are discarded.
After digging through the devices I used during the tests, I just found
some leftover pcap files that show the differences in the received
packets. Since the packets are bigger after my patch, I can't rule out
that packet size instead of the padding may have made a difference here
in getting the ARP requests accepted by the receiver.
I've extracted the ARP requests and you can find them here:
http://nbd.name/arp-broken.pcap
http://nbd.name/arp-working.pcap
- Felix
next prev parent reply other threads:[~2022-05-10 22:06 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 9:40 [PATCH v2] net: dsa: tag_mtk: add padding for tx packets Felix Fietkau
2022-05-10 12:37 ` Vladimir Oltean
2022-05-10 14:52 ` Felix Fietkau
2022-05-10 16:52 ` Vladimir Oltean
2022-05-10 22:06 ` Felix Fietkau [this message]
2022-05-10 22:21 ` Vladimir Oltean
2022-05-11 8:50 ` Felix Fietkau
2022-05-11 9:32 ` Vladimir Oltean
2022-05-11 12:24 ` Felix Fietkau
2022-05-11 13:22 ` Vladimir Oltean
2022-05-11 14:32 ` Andrew Lunn
2022-05-12 8:51 ` Felix Fietkau
2022-05-12 12:39 ` Andrew Lunn
2022-05-12 13:08 ` Felix Fietkau
2022-05-12 15:32 ` Andrew Lunn
2022-05-11 14:39 ` Andrew Lunn
2022-05-10 21:26 ` Jakub Kicinski
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