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

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Date:	Fri, 04 Apr 2008 18:21:22 -0500
From:	Josh Boyer <jwboyer@...il.com>
To:	David Brownell <david-b@...bell.net>
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 Fri, 2008-04-04 at 16:09 -0700, David Brownell wrote:
> On Friday 04 April 2008, Andrew Morton wrote:
> 
> > I'm assuming from the trace that the arm code tried to put that memory
> > under DMA (or at least, passed it into part of the DMA management code to
> > get the various caches sorted out) and that the arm DMA support code
> > doesn't like being given vmalloced memory.
> 
> Actually, Documentation/DMA-Mapping.txt has a section right up
> front called "What memory is DMA'able?" ... which despite its
> ungrammatical title, says clearly:
> 
>   ... 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.

josh

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