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

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Message-ID: <20121016.132755.661591248175727826.hdoyu@nvidia.com>
Date:	Tue, 16 Oct 2012 12:27:55 +0200
From:	Hiroshi Doyu <hdoyu@...dia.com>
To:	"linux@....linux.org.uk" <linux@....linux.org.uk>
CC:	"m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
	"inki.dae@...sung.com" <inki.dae@...sung.com>,
	"arnd@...db.de" <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@...sung.com" <kyungmin.park@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [RFC 0/2] DMA-mapping & IOMMU - physically
 contiguous allocations

Hi Russell,

Russell King - ARM Linux <linux@....linux.org.uk> wrote @ Tue, 16 Oct 2012 10:59:28 +0200:

> On Tue, Oct 16, 2012 at 09:04:34AM +0300, Hiroshi Doyu wrote:
> > 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().
> 
> That situation is covered.  It's the streaming API you're wanting for that.
> dma_map_sg() - but you may need additional cache handling via
> flush_dcache_page() to ensure that your code is safe for all CPU cache
> architectures.
>
> Remember that pages allocated into userspace will be cacheable, so a cache
> flush is required before they can be DMA'd.  Hence the streaming
> API.

Is the syscall "cacheflush()" supposed to be the knob for that?

Or is there any other ones to have more precise control, "clean",
"invalidate" and "flush", from userland in generic way?
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