Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

[Pekka Enberg]

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
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