Re: [PATCH v5 11/18] iommu: exynos: remove useless device_add/remove callbacks

[Laurent Pinchart <laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>]

Hi Joerg,

On Monday 26 January 2015 12:00:59 Joerg Roedel wrote:
> Hi Laurent,
> 
> On Sun, Jan 25, 2015 at 05:38:22PM +0200, Laurent Pinchart wrote:
> > IOMMU groups still seem a bit unclear to me. Will Deacon has nicely
> > explained what they represent in
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2014-December/310816
> > .html. The IOMMU core doesn't make groups
> > mandatory, but requires them in some code paths.
> > 
> > For example the coldplug device add function add_iommu_group() called for
> > all devices already registered when bus_set_iommu() is called will try to
> > warn of devices added multiple times with a WARN_ON(dev->iommu_group).
> > Another example is the iommu_bus_notifier() function which will call the
> > remove_device() operation only when dev->iommu_group isn't NULL.
> > 
> > I'm thus unsure whether groups should be made mandatory, or whether the
> > IOMMU core should be fixed to make them really optional (or, third
> > option, whether there's something I haven't understood properly).
> 
> My plan is to make IOMMU groups mandatory. I am currently preparing and
> RFC patch-set to introduce default-domains (which will be per group). So
> when all IOMMU drivers are converted to make use of default domains the
> iommu groups will be mandatory.

Could the default domain policy be configured by the IOMMU driver ? The ipmmu-
vmsa driver supports four domains only, and serves up to 32 masters, with one 
group per master. A default of one domain per group wouldn't be usable.

-- 
Regards,

Laurent Pinchart