linux-kernel - Re: [PATCH] Fix Oops with Atmel SPI

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Date:	Wed, 14 Apr 2010 09:57:20 +0200
From:	Anders Larsen <al@...rsen.net>
To:	Iwo Mergler <iwo@...l-direct.com.au>
Cc:	linux-mtd@...ts.infradead.org,
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>,
	Ian McDonnell <ian@...ghtstareng.com>,
	Nicolas Pitre <nico@...xnic.net>, linux-kernel@...r.kernel.org,
	Matthias Kaehlcke <matthias@...hlcke.net>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] Fix Oops with Atmel SPI

Hi Iwo,

On 2010-04-14 09:30:41, Iwo Mergler wrote:
> I wouldn't recommend that. MTD erase blocks are 64K or more. In a typical
> embedded system you will not be able to kmalloc that much memory after
> a few day's of operation - the page pool gets fragmented.

the original problem occurs with SPI flashes, which typically have a much
smaller erase block size (and it only occurs when they are driven by an Atmel
SoC SPI controller, hence the #ifdefs)

> A possibly better approach is to arrange for that memory to get allocated
> at driver start time.

The buffer in question is indeed allocated _once_ (at the first write
operation to the device) and only deallocated when the device is unmounted,
so allocating it at driver load time wouldn't make much difference IMHO.

I realize that my patch also affects e.g. parallel NOR flash on the system,
but unless an MTD device is unmounted/remounted over and over again, I don't
see a problem.

Did I miss something else?

> An even better approach would be to change the algorithm to operate on
> a list of smaller allocations, e.g. MTD page size.

That's unfortunately beyond my abilities, I fear.

Cheers
Anders

> Anders Larsen wrote:
> > Tweak MTD's cache allocation to make it work with the atmel DMA'ed SPI.
> > Substitute kmalloc for vmalloc so the cache buffer is mappable as per
> > the Atmel SPI driver's requirements, otherwise an Oops would occur.
> > 
> > The original patch by Ian McDonnell <ian@...ghtstareng.com> was found here:
> > http://lists.infradead.org/pipermail/linux-mtd/2007-December/020184.html
> > 
> > Signed-off-by: Anders Larsen <al@...rsen.net>
> > Cc: Ian McDonnell <ian@...ghtstareng.com>
> > Cc: David Woodhouse <dwmw2@...radead.org>
> > Cc: Matthias Kaehlcke <matthias@...hlcke.net>
> > Cc: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
> > Cc: Nicolas Pitre <nico@...xnic.net>

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