linux-kernel - Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management

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Date:	Mon, 12 Jul 2010 22:57:06 -0700
From:	Zach Pfeffer <zpfeffer@...eaurora.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	linux@....linux.org.uk, ebiederm@...ssion.com,
	linux-arch@...r.kernel.org, dwalker@...eaurora.org, mel@....ul.ie,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, andi@...stfloor.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device
 memory management

FUJITA Tomonori wrote:
> On Thu, 08 Jul 2010 16:59:52 -0700
> Zach Pfeffer <zpfeffer@...eaurora.org> wrote:
> 
>> The problem I'm trying to solve boils down to this: map a set of
>> contiguous physical buffers to an aligned IOMMU address. I need to
>> allocate the set of physical buffers in a particular way: use 1 MB
>> contiguous physical memory, then 64 KB, then 4 KB, etc. and I need to
>> align the IOMMU address in a particular way.
> 
> Sounds like the DMA API already supports what you want.
> 
> You can set segment_boundary_mask in struct device_dma_parameters if
> you want to align the IOMMU address. See IOMMU implementations that
> support dma_get_seg_boundary() properly.

That function takes the wrong argument in a VCM world:

unsigned long dma_get_seg_boundary(struct device *dev);

The boundary should be an attribute of the device side mapping,
independent of the device. This would allow better code reuse.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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