Re: [PATCH 1/2] arm: msm: Add System MMU support.

From: Roedel, Joerg
Date: Wed Aug 04 2010 - 05:49:50 EST

On Tue, Aug 03, 2010 at 02:43:20PM -0400, Stepan Moskovchenko wrote:
> On 8/3/2010 2:23 AM, Roedel, Joerg wrote:
> > A domain is defined by a single page-table which can be modified using
> > the iommu_map/iommu_unmap function calls. I am not completly sure what
> > you mean by an iommu_context. Can you describe what it means in your
> > context?
> Joerg,
> I think with some rework, all my use cases can be handled by your
> existing iommu API. If the domain is treated basically a page table,
> there will be some changes, but I think it can be done. I will push a
> new version of my driver in a few days.
> One thing that may be helpful for the future, however, is maybe
> something like adding iommu_tlb_flush to the ops. I suppose this would
> either have to take a device, or the domain would need to keep a list of
> devices it had been attached to (so that their TLBs can be invalidated).
> But I suppose on the other hand, iommu_map/unmap may be able to just
> implicitly invalidate the TLB also, since TLB invalidation often follows
> map/unmap. What are your thoughts?

Sounds good. I am curious for your patches :-)

For the TLB-flush question, I think it would make sense to add iommu
tlb flushing functions to the IOMMU-API. We currently flush the TLB
implicitly in the map/unmap calls but thats very inefficient. It would
be better to have a seperate function for it in the API. The right
parameter for such a function is a domain. The IOMMU driver knows which
devices are attached to a domain an could easily flush all TLBs.

One alternative I can think of: An iommu_domain_commit() function which
syncs software changes of a domain to the hardware. The map/unmap calls
have to save which parts of the tlb need to be flushed and commit does
flush those parts then (or flush everything).


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