linux-kernel - Re: [PATCH] jffs2 summary allocation

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Date:	Fri, 4 Apr 2008 16:58:38 -0700
From:	David Brownell <david-b@...bell.net>
To:	Josh Boyer <jwboyer@...il.com>
Cc:	linux-arm-kernel@...ts.arm.linux.org.uk,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michael Trimarchi <trimarchimichael@...oo.it>,
	dwmw2@...radead.org, spi-devel-general@...ts.sourceforge.net,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]  jffs2 summary allocation

On Friday 04 April 2008, Josh Boyer wrote:
> 
> >   ... This means specifically that you may _not_ use the
> >   memory/addresses returned from vmalloc() for DMA.  ...
> > 
> > So I'm rather surprised to see *ANY* kernel code trying to do
> > that.  That rule has been in effect for many, many years now.
> 
> I don't think it was intentional.  You're going through several layers
> here:
> 
> JFFS2 -> mtd parts -> mtd dataflash -> atmel_spi.
> 
> Typically MTD drivers aren't doing DMAs to flash and JFFS2 has no idea
> which particular chip driver is being used because it's abstracted by
> MTD.

That's true ... although I can imagine using DMA to
avoid dcache trashing if its setup cost is low enough,
with either NAND or NOR chips.

Still:  in this context vmalloc() is wrong.

- Dave
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