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

[Zach Pfeffer <zpfeffer@codeaurora.org>]

FUJITA Tomonori wrote:
> On Thu, 08 Jul 2010 16:59:52 -0700
> Zach Pfeffer <zpfeffer@codeaurora.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.

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