Re: [PATCH v2 RESEND 2/2] ARM: local timers: add timer support using IO mapped register

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Tue, Oct 02, 2012 at 12:27:04PM +0100, Dave Martin wrote:
> On Fri, Sep 28, 2012 at 06:15:53PM +0100, Lorenzo Pieralisi wrote:
> > On Fri, Sep 28, 2012 at 04:57:46PM +0100, Dave Martin wrote:

[...]

> > There must be a common way for all devices to link to the topology, though.
> > 
> > The topology must be descriptive enough to cater for all required cases
> > and that's what Mark with PMU and all of us are trying to come up with, a solid
> > way to represent with DT the topology of current and future ARM systems.
> > 
> > First idea I implemented and related LAK posting:
> > 
> > http://lists.infradead.org/pipermail/linux-arm-kernel/2012-January/080873.html
> > 
> > Are "cluster" nodes really needed or "cpu" nodes are enough ? I do not
> > know, let's get this discussion started, that's all I need.
> 
> One thing which now occurs to me on this point it that if we want to describe
> the CCI properly in the DT (yes) then we need a way to describe the mapping
> between clusters and CCI slave ports.  Currently that knowledge just has to
> be a hard-coded hack somewhere: it's not probeable at all.

That's definitely a good point. We can still define CCI ports as belonging
to a range of CPUs, but that's a bit of a stretch IMHO.

> I'm not sure how we do that, or how we describe the cache topology, without
> the clusters being explicit in the DT
> 
> ...unless you already have ideas ?

Either we define the cluster node explicitly or we can always see it as a
collection of CPUs, ie phandles to "cpu" nodes. That's what the decision
we have to make is all about. I think that describing it explicitly make
sense, but we need to check all possible use cases to see if that's
worthwhile.

Lorenzo