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

On Wed, 14 Jul 2010 13:11:49 -0700
Zach Pfeffer [off-list ref] wrote:

On Wed, Jul 14, 2010 at 10:59:38AM +0900, FUJITA Tomonori wrote:

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On Tue, 13 Jul 2010 05:14:21 -0700
Zach Pfeffer [off-list ref] wrote:

quoted

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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.

Yes, and that's what the implementation does - and all the other
implementations that need to do this same thing. Why not solve the
problem once?

Why we we need a new abstraction layer to solve the problem that the
current API can handle?

The above two operations don't sound too complicated. The combination
of the current API sounds much simpler than your new abstraction.

Please show how the combination of the current APIs doesn't
work. Otherwise, we can't see what's the benefit of your new
abstraction.