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

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Message-ID: <CAHkRjk52DH9_QPQwGF0HUcjsH3+WTRCF41uDKJW7LyxD65pJdw@mail.gmail.com>
Date:	Tue, 16 Oct 2012 11:04:29 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Hiroshi Doyu <hdoyu@...dia.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Inki Dae <inki.dae@...sung.com>, 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

On 16 October 2012 09:59, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> 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.

For user-allocated pages you first need get_user_pages() to make sure
they are in memory (and will stay there). This function also calls
flush_dcache_page(). Then you can build the sg list for dma_map_sg().

-- 
Catalin
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