Re: [Xen-devel] [PATCH 7/7] xen/arm: get the number of cpus from device tree

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-11-15 at 15:26 +0000, Stefano Stabellini wrote:
> On Thu, 15 Nov 2012, Ian Campbell wrote:
> > On Tue, 2012-11-13 at 15:42 +0000, Stefano Stabellini wrote:
> > > diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
> > > index 3d1f0f4..5b6dab9 100644
> > > --- a/xen/common/device_tree.c
> > > +++ b/xen/common/device_tree.c
> > > @@ -153,6 +153,25 @@ const char *device_tree_bootargs(const void *fdt)
> > >      return prop->data;
> > >  }
> > >  
> > > +int device_tree_cpus(const void *fdt)
> > > +{
> > > +    int node = 0, depth = 1;
> > > +    int cpus = 0;
> > > +
> > > +    node = fdt_path_offset(fdt, "/cpus/cpu");
> > > +    if ( node < 0 )
> > > +        return 1; /* we have at least one cpu */
> > > +
> > > +    while ( node >= 0 && depth >= 0 ) {
> > > +        if ( strncmp(fdt_get_name(fdt, node, NULL), "cpu", 3) )
> > > +            continue;
> > > +        node = fdt_next_node(fdt, node, &depth);
> > > +        cpus++;
> > 
> > Do we not need to track the largest <n> for each cpu@<n> which we see,
> > in order to handle systems with e.g. CPUs 0, 1, 4 & 5?
> 
> Actually the hardware ID is expressed by the <reg> propery.
> Maybe we should set the corresponding ID in cpu_present_map from
> device_tree_cpus?

I'm not sure what you mean.

> > There are some helpers in device_tree.c to walk over trees like this,
> > are none of them suitable?
>  
> Do you mean device_tree_node_matches?
> Yes, I can use that instead of strncmp. I'll do that.

You should , but that's not what I was talkig about ;-)

I was thinking of device_tree_for_each_node but I suppose that doesn't
quite fit? But perhaps you can integrate with early_scan_node?

Ian.


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