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Date: Tue, 11 May 2010 23:47:20 +0300
From: Pekka Enberg <penberg@cs.helsinki.fi>
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To: Mike Frysinger <vapier.adi@gmail.com>
CC: Christoph Lameter <cl@linux.com>, Matt Mackall <mpm@selenic.com>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Oskar Schirmer <os@emlix.com>,
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       "=?UTF-8?B?RGFuaWVsIEdsw7Zja25lcg==?=" <dg@emlix.com>,
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       Nick Piggin <npiggin@suse.de>, David Rientjes <rientjes@google.com>,
       David Brownell <dbrownell@users.sourceforge.net>,
       Grant Likely <grant.likely@secretlab.ca>
Subject: Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines
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Mike Frysinger wrote:
> On Tue, May 11, 2010 at 16:38, Pekka Enberg wrote:
>> Mike Frysinger wrote:
>>> that is a question for David/Grant.  i'm not the SPI core maintainer,
>>> i'm merely watching over some SPI drivers.  however, this answer also
>>> doesnt sound like it's thinking big enough because what you're
>>> proposing isnt specific to the SPI bus -- any time a DMA safe buffer
>>> is needed dynamically, this function could be used.
>> Well, we have dma_alloc_coherent(), shouldn't you be using that instead?
> 
> my understanding is that dma_alloc_coherent() gives you a buffer that
> is always coherent.  the SPI layers take care of flushing and such on
> the fly which means allocating coherent memory is overkill and bad for
> performance.

OK, I'm out of my expert area here but if dma_alloc_coherent() doesn't 
work for you, you should probably extend the DMA API, not kmalloc().

			Pekka