linux-kernel - Re: [PATCH 1/5] dma: create dma_generic_alloc/free

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Message-ID: <1256610399.19177.3.camel@2710p.home>
Date:	Mon, 26 Oct 2009 20:26:39 -0600
From:	Alex Williamson <alex.williamson@...com>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	dwmw2@...radead.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 1/5] dma: create dma_generic_alloc/free_coherent()

On Tue, 2009-10-27 at 09:57 +0900, Paul Mundt wrote:
> On Mon, Oct 26, 2009 at 05:24:58PM -0600, Alex Williamson wrote:
> > Move dma_generic_alloc_coherent() out of x86 code and create
> > corresponding dma_generic_free_coherent() for symmetry.  These
> > can then be used by IOMMU drivers attempting to implement
> > passthrough mode.
> > 
> Except that dma_generic_alloc_coherent() is only "generic" for platforms
> with consistent DMA. Everyone else will need a cacheflush and potentially
> a remap. It's not even obvious from looking at the consistent DMA
> platforms that they'll be able to use it out of the box due to expecting
> something other than page_address(), which all suggests that this is
> better off remaining an x86-only routine.
> 
> This is also making changes to the DMA-API without any documentation
> updates and without consulting with any other architecture people.

Ok, thanks for the feedback.  Let's forget this patch and I'll see how
amenable David is to doing something within intel-iommu since it only
supports platforms with consistent DMA.  Thanks,

Alex

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