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: > > 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. 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 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
