linux-kernel - Re: [net-next PATCH 1/2] net: ravb: Fix maximum MTU for GbEth devices

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Date: Mon, 17 Jun 2024 17:07:59 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Paul Barker <paul.barker.ct@...renesas.com>
Cc: Sergey Shtylyov <s.shtylyov@....ru>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Niklas Söderlund
 <niklas.soderlund+renesas@...natech.se>, Biju Das
 <biju.das.jz@...renesas.com>, Claudiu Beznea
 <claudiu.beznea.uj@...renesas.com>, Lad Prabhakar
 <prabhakar.mahadev-lad.rj@...renesas.com>, Mitsuhiro Kimura
 <mitsuhiro.kimura.kc@...esas.com>, netdev@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [net-next PATCH 1/2] net: ravb: Fix maximum MTU for GbEth
 devices

On Sat, 15 Jun 2024 11:30:37 +0100 Paul Barker wrote:
> The datasheets for all SoCs using the GbEth IP specify a maximum
> transmission frame size of 1.5 kByte. I've confirmed through internal
> discussions that support for 1522 byte frames has been validated, which
> allows us to support the default MTU of 1500 bytes after reserving space
> for the Ethernet header, frame checksums and an optional VLAN tag.

But what's the user impact? If we send a bigger frame the IP will hang?
Drop the packet? Something else?
"Validated" can also mean "officially supported" sometimes vendors just
say that to narrow down the test matrix :(