Re: RFC: extend iommu_ops with domain attributes API

[Joerg Roedel <joro@8bytes.org>]

On Tue, Jan 10, 2012 at 10:22:36AM -0600, Stuart Yoder wrote:
> As we work on mapping the Freescale IOMMU (called PAMU) into the existing
> Linux iommu infrastructure, one issue is that we have additional domain
> attributes that need to be set.   This was discussed briefly a month ago
> or so and I believe there was a need for a similar mechanism by IBM.
> 
> We are proposing a couple of APIs to be added to iommu_ops to
> get/set domain attributes:
> 
>    int domain_set_attr(struct iommu_domain *domain, int attr_type, void *data);
>    int domain_get_attr(struct iommu_domain *domain, int attr_type, void *data);

Yes, something similar to that interface is required to support
GART-like IOMMUs too.
I prefer to split the attr-type into generic ones supported by many
IOMMU drivers and implementation specific ones required by your PAMU for
example.

> A couple of the attributes I'm considering PAMU specific with a generic
> enable attribute:
> 
>    enum iommu_attr_type {
>        IOMMU_ATTR_PAMU_GEOMETRY,       // the PAMU geometry for the domain

This should be a generic attribute. It makes sense for nearly all IOMMUs
to export geometry information.

>        IOMMU_ATTR_PAMU_STASH,          // stash characteristics for a domain

That one is fine.

>        IOMMU_ATTR_ENABLE

I do not get the need of this one. Can you explain why you need to
enable/disable a domain? What happens on the hardware side when you do
that?


	Joerg