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

[FUJITA Tomonori]

On Tue, 13 Jul 2010 05:14:21 -0700
Zach Pfeffer <zpfeffer at codeaurora.org> wrote:

> > You mean that you want to specify this alignment attribute every time
> > you create an IOMMU mapping? Then you can set segment_boundary_mask
> > every time you create an IOMMU mapping. It's odd but it should work.
> 
> Kinda. I want to forget about IOMMUs, devices and CPUs. I just want to
> create a mapping that has the alignment I specify, regardless of the
> mapper. The mapping is created on a VCM and the VCM is associated with
> a mapper: a CPU, an IOMMU'd device or a direct mapped device.

Sounds like you can do the above with the combination of the current
APIs, create a virtual address and then an I/O address.

The above can't be a reason to add a new infrastructure includes more
than 3,000 lines.
 

> > Another possible solution is extending struct dma_attrs. We could add
> > the alignment attribute to it.
> 
> That may be useful, but in the current DMA-API may be seen as
> redundant info.

If there is real requirement, we can extend the DMA-API.