Re: [RFC 0/6] iommu: generic api migration and grouping

Arnd Bergmann
2011-06-03T15:53:38Z

On Friday 03 June 2011, Ohad Ben-Cohen wrote:
> First stab at iommu consolidation:

Hi Ohad,

Great to see your progress here!

> - Migrate OMAP's iommu driver to the generic iommu API. With this in hand,
> users can now start using the generic iommu layer instead of calling
> omap-specific iommu API.
>
> New code that requires functionality missing from the generic iommu api,
> will add that functionality in the generic framework (e.g. adding framework
> awareness to multi page sizes, supported by the underlying hardware, will
> avoid the otherwise-inevitable code duplication when mapping a memory
> region).
>
> OMAP-specific api that is still exposed in the omap iommu driver can
> now be either moved to the generic iommu framework, or just removed (if not
> used).
>
> This api (and other omap-specific primitives like struct iommu) needs to
> be omapified (i.e. renamed to include an 'omap_' prefix). At this early
> point of this patch set this is too much churn though, so I'll do that
> in the following iteration, after (and if), the general direction is
> accepted.

Sounds all good.

> - Migrate OMAP's iovmm (virtual memory manager) driver to the generic
> iommu API. With this in hand, iovmm no longer uses omap-specific api
> for mapping/unmapping operations. Nevertheless, iovmm is still coupled
> with omap's iommu even with this change: it assumes omap page sizes,
> and it uses omap's iommu objects to maintain its internal state.
>
> Further generalizing of iovmm strongly depends on our broader plans for
> providing a generic virtual memory manager and allocation framework
> (which, as discussed, should be separated from a specific mapper).
>
> iovmm has a mainline user: omap3isp, and therefore must be maintained,
> but new potential users will either have to generalize it, or come up
> with a different generic framework that will replace it.

I think the future of iovmm is looking not so good. Marek Szyprowski
is working on a generic version of the dma-mapping API (dma_map_ops)
based on the iommu API. As far as I can tell, once we have that in
place, we you can migrate omap3isp from iovmm to dma-mapping and
remove iovmm.

Of course if there are things missing from the dma-mapping API
that are present in iovmm, we should know about them so that we can
extend the dma-mapping API accordingly.

> - Migrate OMAP's iommu mainline user, omap3isp, to the generic API as well
> (so it doesn't break). As with iovmm, omap3isp still depends on
> omap's iommu, mainly because iovmm depends on it, but also for
> iommu context saving and restoring.
>
> It is definitely desirable to completely remove omap3isp's dependency
> on the omap-specific iommu layer, and that will be possible as the
> required functionality will be added to generic framework.

ok.

> - Create a dedicated iommu drivers folder (and put the base iommu code there)
>
> - Move OMAP's and MSM's iommu drivers to that drivers iommu folder
>
> Putting all iommu drivers together will ease finding similarities
> between different platforms, with the intention of solving problems once,
> in a generic framework which everyone can use.
>
> I've only moved the omap and msm implementations for now, to demonstrate
> the idea (and support the ARM diet :), but if this is found desirable,
> we can bring in intel-iommu.c and amd_iommu.c as well.

Yes, very good idea.

Arnd