netdev - Re: [net-next PATCH 2/2] net: ravb: Fix R-Car RX frame size limit

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Date: Sun, 16 Jun 2024 03:23:17 +0200
From: Andrew Lunn <andrew@...n.ch>
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>,
	Jakub Kicinski <kuba@...nel.org>, 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 2/2] net: ravb: Fix R-Car RX frame size limit

On Sat, Jun 15, 2024 at 11:30:38AM +0100, Paul Barker wrote:
> The RX frame size limit should not be based on the current MTU setting.
> Instead it should be based on the hardware capabilities.

This is a bit odd. MTU is Maximum Transmission Unit, so clearly is
about Tx. MRU does not really exist. Does TCP allow for asymmetric
MTU/MRU? Does MTU discovery work correctly for this?

In general, it seems like drivers implement min(MTU, MRU) and nothing
more. Do you have a real use case for this asymmetry?

      Andrew