linux-kernel - Re: [PATCH net-next v3 1/4] net: stmmac: Switch to zero-copy in non-XDP RX path

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Message-ID: <ccbecd2a-7889-4389-977e-10da6a00391c@lunn.ch>
Date: Thu, 23 Jan 2025 22:48:42 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Brad Griffis <bgriffis@...dia.com>
Cc: Furong Xu <0x1207@...il.com>, Jon Hunter <jonathanh@...dia.com>,
	netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Joe Damato <jdamato@...tly.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>, xfr@...look.com,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH net-next v3 1/4] net: stmmac: Switch to zero-copy in
 non-XDP RX path

> Just to clarify, the patch that you had us try was not intended as an actual
> fix, correct? It was only for diagnostic purposes, i.e. to see if there is
> some kind of cache coherence issue, which seems to be the case?  So perhaps
> the only fix needed is to add dma-coherent to our device tree?

That sounds quite error prone. How many other DT blobs are missing the
property? If the memory should be coherent, i would expect the driver
to allocate coherent memory. Or the driver needs to handle
non-coherent memory and add the necessary flush/invalidates etc.

	Andrew