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

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Message-ID: <d5e2d054-e309-4382-a211-9fa9a0e83783@lunn.ch>
Date: Tue, 13 Aug 2024 16:06:40 +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

> Apologies, my response here is abysmally late due to illness, other
> priorities and then the loss of my main dev box.

Not a problem, life happens.

> As you've said, a number of devices do not limit received packet size to
> the MTU. There are many applications, other than a gateway, where using
> jumbo packets in even just one direction would be beneficial. For
> example if an application needs to receive large amounts of data but
> only needs to send back control and acknowledgement messages. I think we
> should support this where possible. This is the thought behind the first
> patch in this series as the GbEth IP present in the RZ/G2L and other
> Renesas SoCs has a very asymmetric capability (it can receive 8000 byte
> frames but only transmit 1522 byte frames).
> 
> If we explicitly do not wish to support this, that restriction should be
> documented and then (maybe over time) handled uniformly for all network
> drivers.
> 
> I'm planning to submit v2 of this series shortly.

Does the hardware support scatter/gather? How does supporting jumbo
receive affect memory usage? Can you give the hardware a number of 2K
buffers, and it will use one for a typical packet, and 4 for a jumbo
frame?

	Andrew