> Hi Stephan,
>
> On Fri, Jul 30, 2010 at 01:19:06AM -0400,
stepanm@codeaurora.org wrote:
> > Unlike a more traditional system with one IOMMU between the bus and
> > memory, MSM has multiple IOMMUs, with each one hard-wired to a dedicated
> > device. Furthermore, each IOMMU can have more than one translation
> > context. One of the use cases is being able to create mappings within
> > multiple instances of one context, and arbitrarily context-switch the
> > IOMMU on the fly.
>
> The IOMMU-API supports multiple IOMMUs (at least multiple AMD/Intel
> IOMMUs). But the face that there are more than one IOMMU is hidden in
> the backend driver implementation. The API itself only works with
> domains and devices. The IOMMU driver needs to know which IOMMU it needs
> to program for a given device. If I understand the concept of your
> hardware correctly you also have this information.
>
> > It sounds like the domain abstraction and attach_device/detach_device can
> > encapsulate this rather nicely and I am in the process of updating my
> > driver to fit this framework.
> >
> > My problem, however, is with iommu_domain_alloc(). This will set up a
> > domain and call the ops function to initialize it, but I want to be able
> > to pass it an ???IOMMU id" that will tell the underlying driver which IOMMU
> > (and which "stream id") is to be associated with that domain instance.
> > This can be a void* parameter that gets passed through to domain_init. I
> > feel like this change will make it easy to deal with multiple
> > IOMMUs/translation contexts, and implementations that have only a singular
> > IOMMU/translation context are free to ignore that parameter.
>
> In the means of the IOMMU-API the domain is the abstraction of an
> address space (in other words a page table). The IOMMU(s) which this domain
> is later assigned to are determined by the iommu_attach_device calls.
> I think the right way to go here is to create the concept of a
> device-context in the IOMMU-API and add functions like
>
> iommu_attach_context(struct iommu_domain *domain,
> struct iommu_context *ctxt);
> iommu_detach_context(struct iommu_context *ctxt);
>
> This would work if you can determine in your iommu-driver which iommu
> you need to program for which device. What do you think?
>
