[RFC 01/10] iommu: Add IOMMU device registry

On Fri, Jul 04, 2014 at 02:47:10PM +0100, Thierry Reding wrote:

On Fri, Jul 04, 2014 at 01:05:30PM +0200, Joerg Roedel wrote:

quoted

On Thu, Jun 26, 2014 at 10:49:41PM +0200, Thierry Reding wrote:

quoted

Add an IOMMU device registry for drivers to register with and implement
a method for users of the IOMMU API to attach to an IOMMU device. This
allows to support deferred probing and gives the IOMMU API a convenient
hook to perform early initialization of a device if necessary.

Can you elaborate on why exactly you need this? The IOMMU-API is
designed to hide any details from the user about the available IOMMUs in
the system and which IOMMU handles which device. This looks like it is
going in a completly different direction from that.

I need this primarily to properly serialize device probing order.
Without it the IOMMU may be probed later than its clients, in which case
the client drivers will assume that there is no IOMMU (iommu_present()
for the parent bus fails).

I can also vouch for needing *a* solution to this problem. The ARM SMMU (and
I think others) rely on initcall ordering rather than the driver probing
model to ensure the IOMMU is probed before any of its masters.

Will