linux-kernel - Re: Hit BUG_ON in dma-mapping.c:425 (RFC)

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Message-ID: <1300964887.2735.84.camel@localhost>
Date:	Thu, 24 Mar 2011 13:08:07 +0200
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Patrice VILCHEZ <patrice.vilchez@...el.com>,
	Hong XU <hong.xu@...el.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Andrew Victor <linux@...im.org.za>,
	linux-mtd <linux-mtd@...ts.infradead.org>
Subject: Re: Hit BUG_ON in dma-mapping.c:425 (RFC)

On Thu, 2011-03-24 at 09:27 +0000, Russell King - ARM Linux wrote:
> The only real answer I can give is: if you want to deal with DMA, you
> absolutely must conform to the restrictions on DMA which means that you
> can't pass vmalloc addresses to the DMA API.

I see, thanks. Well, I do not see any issues with changing MTD-related
SW (JFFS2, UBI, UBIFS, etc) to use kmalloc. But this would require som
non-trivial efforts, although I believe this is doable.

Basically, we have to work with entire eraseblocks often, which may be
128KiB or 256KiB or even 512KiB nowadays. And we vmalloc the
eraseblock-sized buffers in these cases.

We could instead work with arrays of pages (or multiple pages), and then
do things like readv/writev. But this requires a brave knight who'd come
and just implemented this, or a company who'd fund someone to work on
this.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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