On Thu, Feb 01, 2024 at 04:03:59PM +0100, Stefan Wiehler wrote:
> > Does this mean the /cpus property is like a default for when a CPU node
> > doesn't specify the clock frequency, or does it mean that the /cpus
> > property should only exist when all the values for each CPU are
> > identical and thus the individual CPU node clock frequency should
> > not be specified.
>
> Good question, the device tree specification in Section 3.7 [1] says:
>
> > The /cpus node may contain properties that are common across cpu
> nodes. See Section 3.8 for details.
>
> And in Section 3.8 [2]:
>
> > Properties that have identical values across cpu nodes may be placed
> > in the /cpus node instead. A client program must first examine a
> > specific cpu node, but if an expected property is not found then it
> > should look at the parent /cpus node. This results in a less verbose
> > representation of properties which are identical across all CPUs.
>
> So I think it is pretty clear that it should only be used for
> common/identical values.
Thanks for the clarification.
As this is DT specified behaviour, I question whether it should be
implemented in arch/arm/kernel/topology.c - what I'm meaning is
a helper such as:
const void *of_get_cpu_property(const struct device_node *node,
const char *name, int *lenp)
{
const void *res;
res = of_get_property(node, name, lenp);
if (!res) {
node = of_find_node_by_path("/cpus");
if (node)
res = of_get_property(node, name, lenp);
of_node_put(node);
}
return res;
}
?
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