linux-kernel - RE: [PATCH v2] net/macb: Use non-coherent memory for rx buffers

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B70DB@saturn3.aculab.com>
Date:	Wed, 5 Dec 2012 15:22:14 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Nicolas Ferre" <nicolas.ferre@...el.com>
Cc:	"David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	"Joachim Eastwood" <manabian@...il.com>,
	"Jean-Christophe PLAGNIOL-VILLARD" <plagnioj@...osoft.com>,
	"Havard Skinnemoen" <havard@...nnemoen.net>
Subject: RE: [PATCH v2] net/macb: Use non-coherent memory for rx buffers

> Well, for the 10/100 MACB interface, I am stuck with 128 Bytes buffers!
> So this use of pages seems sensible.

If you have dma coherent memory you can make the rx buffer space
be an array of short buffers referenced by adjacent ring entries
(possibly with the last one slightly short to allow for the
2 byte offset).
Then, when a big frame ends up in multiple buffers, you need
a maximum of two copies to extract the data.

	David



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