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

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

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.


	Joerg