Re: vfio / iommu domain attributes

[Joerg Roedel <joerg.roedel@amd.com>]

On Wed, Dec 07, 2011 at 09:54:39AM -0600, Stuart Yoder wrote:
> Alex, Alexey I'm wondering if you've had any new thoughts on this over
> the last week.
> 
> For Freescale, our iommu domain attributes would look something like:
>     -domain iova base address
>     -domain iova window size

I agree with that.

>     -domain enable/disable
>     -number of subwindows
>     -operation mapping table index
>     -stash destination CPU
>     -stash target (cache– L1, L2, L3)

Why does the user of the IOMMU-API need to have control over these
things?

> These are all things that need to be set by the creator of the domain.
> 
> Since the domain attributes are going to be so different for each platform does
> it make sense to define a new iommu_ops call back that just takes a void pointer
> that can be implemented in a platform specific way?   For example:
> 
>     struct iommu_ops {
>         [cut]
>         int (*domain_set_attrs)(struct iommu_domain *domain,
>                               void *attrs);
>         int (*domain_get_attrs)(struct iommu_domain *domain,
>                               void *attrs);
>     }

A void pointer is certainly the worst choice for an interface. I think
it is better to have at least a set of common attributes. Somthing like
this:

iommu_domain_set_attr(struct iommu_domain *domain, enum attr_type, void *data)
iommu_domain_get_attr(struct iommu_domain *domain, enum attr_type, void *data)

The iova base/size options make sense for more IOMMUs than just
Freescale. For example it would allow to manage GART-like IOMMUs with
the IOMMU-API too.


	Joerg

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