linux-kernel - Re: [Linaro-mm-sig] [RFC 0/2] DMA-mapping & IOMMU

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Message-ID: <20121016090434.7d5e088152a3e0b0606903c8@nvidia.com>
Date:	Tue, 16 Oct 2012 09:04:34 +0300
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Inki Dae <inki.dae@...sung.com>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-tegra@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [RFC 0/2] DMA-mapping & IOMMU - physically
 contiguous allocations

Hi Inki/Marek,

On Tue, 16 Oct 2012 02:50:16 +0200
Inki Dae <inki.dae@...sung.com> wrote:

> 2012/10/15 Marek Szyprowski <m.szyprowski@...sung.com>:
> > Hello,
> >
> > Some devices, which have IOMMU, for some use cases might require to
> > allocate a buffers for DMA which is contiguous in physical memory. Such
> > use cases appears for example in DRM subsystem when one wants to improve
> > performance or use secure buffer protection.
> >
> > I would like to ask if adding a new attribute, as proposed in this RFC
> > is a good idea? I feel that it might be an attribute just for a single
> > driver, but I would like to know your opinion. Should we look for other
> > solution?
> >
> 
> In addition, currently we have worked dma-mapping-based iommu support
> for exynos drm driver with this patch set so this patch set has been
> tested with iommu enabled exynos drm driver and worked fine. actually,
> this feature is needed for secure mode such as TrustZone. in case of
> Exynos SoC, memory region for secure mode should be physically
> contiguous and also maybe OMAP but now dma-mapping framework doesn't
> guarantee physically continuous memory allocation so this patch set
> would make it possible.

Agree that the contigous memory allocation is necessary for us too.

In addition to those contiguous/discontiguous page allocation, is
there any way to _import_ anonymous pages allocated by a process to be
used in dma-mapping API later?

I'm considering the following scenario, an user process allocates a
buffer by malloc() in advance, and then it asks some driver to convert
that buffer into IOMMU'able/DMA'able ones later. In this case, pages
are discouguous and even they may not be yet allocated at
malloc()/mmap().
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