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

On Tue, Oct 02, 2012 at 02:44:44PM +0100, Lorenzo Pieralisi wrote:

On Tue, Oct 02, 2012 at 12:27:04PM +0100, Dave Martin wrote:

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On Fri, Sep 28, 2012 at 06:15:53PM +0100, Lorenzo Pieralisi wrote:

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On Fri, Sep 28, 2012 at 04:57:46PM +0100, Dave Martin wrote:

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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.

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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.

How is the cache topology described today (forgive my laziness in not
answering this question for myself)?  The issues are somewhat similar.

I still have some misgivings about describing clusters in terms of sets of
CPUs.  For example, when we boot up a cluster, we have to set up ... the
cluster.  This is a distinct thing which we must set up in addition to
any of the actual CPUs.

There is a strict child/parent relationship between clusters and CPUs, so
a tree of nodes does seem the most natural description ... but I'm not
aware of all the background to this discussion.

Cheers
---Dave