linux-kernel - Re: [PATCH] mmc-atmel : fix kunmap wrong usage

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Message-Id: <200706221621.42000.marc.pignat@hevs.ch>
Date:	Fri, 22 Jun 2007 16:21:40 +0200
From:	Marc Pignat <marc.pignat@...s.ch>
To:	Nicolas Ferre <nicolas.ferre@....atmel.com>
Cc:	Hugh Dickins <hugh@...itas.com>,
	ARM Linux Mailing List 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Andrew Victor <andrew@...people.com>,
	Pierre Ossman <drzeus@...eus.cx>
Subject: Re: [PATCH] mmc-atmel : fix kunmap wrong usage

On Friday 22 June 2007 15:34, Nicolas Ferre wrote:
> Hugh Dickins :
> > Aren't you just guessing there?  Those kunmap_atomics in at91_mci.c
> > may look wrong to you, but they're not incorrect (so long as sg->offset
> > falls within the page, as it must do here to make sense of the page).
> > Especially not on ARM, where kunmap_atomic actually has no interest
> > in the argument passed.  And the oops was in the flush_dcache_page.
> > 
> > If you actually reproduced Nicolas' problem on ARM, and verified
> > that your patch then fixes it, please let us know: that will be
> > remarkably interesting.
> 
> Patch tested without success. Indeed, I always see the Oops with 
> Marc's patch.
So, it's really interesting, it worked really for me (oops without patch) and
no oops with it. My hardware is a custom board with an at91rm9200.

I had a look the the kunmap_atomic function, and I _really_ don't understand
how this patch can do something :-/

And last but not least, my patch is completly wrong...
void *kmap_atomic(...);
unsigned int *buffer = kmap_atomic(...) + sg->offset; // addition in u8*
kunmap_atomic(buffer - sg->offset); // <- sub in u32*

-> please forget my patch

Regards

Marc


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