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

[FUJITA Tomonori]

On Wed, 14 Jul 2010 13:11:49 -0700
Zach Pfeffer <zpfeffer at codeaurora.org> wrote:

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