Re: [PATCH v2] devicetree: Add generic IOMMU device tree bindings

Will Deacon
2014-06-25T10:14:09Z

On Wed, Jun 25, 2014 at 11:12:13AM +0100, Arnd Bergmann wrote:
> On Wednesday 25 June 2014 10:57:36 Will Deacon wrote:
> > So far, I've been avoiding the hardcoding. However, you could potentially
> > build a system with a small number of SMRs (compared to the number of
> > StreamIDs) and allocate the StreamIDs in such a way that I think the dynamic
> > configuration would be NP complete if we require an optimal SMR allocation.
> >
> > However:
> >
> > (1) I don't know of a system where this is the case
> > (2) Not much work has been done on improving the dynamic allocator yet
> >
> > which is why I'm still favouring dynamic configuration in the driver.
> >
> > The other thing I forgot to mention earlier is that we need to support
> > device hotplug in the future, so some level of dynamic configuration
> > will always be required.
>
> Ok, got it. So we just hope that we can make dynamic configuration
> work all the time, but if it all fails, then we come up with a
> hardcoded configuration method.
>
> I guess this could be done similarly to how we handle clocks on
> a lot of systems: generally these are dynamic, but you have the
> option to provide hints in the clock controller node about how
> you expect things to be configured.
>
> For the SMMU that could mean that (if we get into the situation you
> describe), we add optional properties to the SMMU node itself
> describing how we expect the SMRs to be used.

That sounds good to me! Thanks for the discussion.

Will