linux-kernel - Re: [PATCH] x86: enable DMA CMA with swiotlb

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Date:	Sat, 23 Nov 2013 22:59:01 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH] x86: enable DMA CMA with swiotlb

2013/11/23 H. Peter Anvin <hpa@...or.com>:
> On 11/22/2013 04:27 AM, Akinobu Mita wrote:
>>
>> I'm currently working for integrating DMA CMA with intel-iommu which
>> I can test.  Regardless of which dma ops is actually used, I would
>> like to allocate large contiguous memory with dma_alloc_coherent()
>> and tell the base address to the device.
>>
>> We can use mem= or crashkernel= to reserve host memory, but it is
>> complicated and unables to work with real IOMMU.
>>
>
> If you have a real iotlb, why would you need contiguous memory?

Because allocating large memory by dma_alloc_coherent() with intel-iommu
fails.  intel_alloc_coherent() allocates memory by alloc_pages() and
then maps it by __intel_map_single().

What I'm trying change wit inte-iommu is adding the same scheme done
by dma_generic_alloc_coherent(), i.e. trying to allocate memory by
dma_alloc_from_contiguous() and alloc_pages() is used as a fallback.
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