From mboxrd@z Thu Jan  1 00:00:00 1970
Subject: Re: Hit BUG_ON in dma-mapping.c:425 (RFC)
From: Artem Bityutskiy <dedekind1@gmail.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
In-Reply-To: <20110324082521.GB9844@n2100.arm.linux.org.uk>
References: <4D24A108.2080609@atmel.com> <4D8AFE45.8050609@atmel.com>
	<20110324082521.GB9844@n2100.arm.linux.org.uk>
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Date: Thu, 24 Mar 2011 10:36:18 +0200
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Cc: Hong XU <hong.xu@atmel.com>, Nicolas Ferre <nicolas.ferre@atmel.com>,
	Patrice VILCHEZ <patrice.vilchez@atmel.com>,
	Linux Kernel list <linux-kernel@vger.kernel.org>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>,
	Andrew Victor <linux@maxim.org.za>,
	"'linux-arm-kernel@lists.infradead.org'"
	<linux-arm-kernel@lists.infradead.org>
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On Thu, 2011-03-24 at 08:25 +0000, Russell King - ARM Linux wrote:
> On Thu, Mar 24, 2011 at 04:18:13PM +0800, Nicolas Ferre wrote:
> > diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
> > --- a/drivers/spi/atmel_spi.c
> > +++ b/drivers/spi/atmel_spi.c
> > @@ -647,6 +647,22 @@ static void atmel_spi_next_message(struct spi_master *master)
> >  	atmel_spi_next_xfer(master, msg);
> >  }
> >  
> > +static void *adjust_buffer_location(struct device *dev, void *buf)
> > +{
> > +	if (likely(buf < high_memory)) {
> > +		return buf;
> > +	} else {
> > +		struct page *pg;
> > +
> > +		pg = vmalloc_to_page(buf);
> > +		if (pg == 0) {
> > +			dev_err(dev, "failed to vmalloc_to_page\n");
> > +			return NULL;
> > +		}
> > +		return page_address(pg) + ((size_t)buf & ~PAGE_MASK);
> > +	}
> > +}
> > +
> 
> This really doesn't fix the problem.  If the page is read or written via
> the vmalloc mapping, you'll have stale data.
> 
> DMA to vmalloc areas is dodgy at best.

This topics pops up often. So what is the right fix? And sorry for my
ignorance.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)