Quoting Viresh Kumar (2014-07-01 04:14:04)

On 1 July 2014 00:03, Rob Herring [off-list ref] wrote:

quoted

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What about comparing "clocks" property in cpu DT nodes?

What if a different clock is selected for some reason.

I don't know why that will happen for CPUs sharing clock line.

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I think a clock api function would be better.

@Mike: What do you think? I think we can get a clock API for
this.

I can't help but think this is a pretty ugly solution. Why not specify
the nature of the cpu clock(s) in DT directly? There was a thread
already that discussed adding such a property to the CPU DT binding but
it seems to have gone cold[1]. Furthermore my mailer sucks and I see now
that my response to that thread never hit the list due to mangled
headers. Here is a copy/paste of my response to the aforementioned
thread:

"""
I'll join the bikeshedding.

The hardware property that matters for cpufreq-cpu0 users is that a
multi-core CPU uses a single clock input to scale frequency across all
of the cores in that cluster. So an accurate description is:

scaling-method = "clock-ganged"; //hardware-people-speak

Or,

scaling-method = "clock-shared"; //software-people-speak

Versus independently scalable CPUs in an SMP cluster:

scaling-method = "independent"; //x86, Krait, etc.

Or perhaps instead of "independent" at the parent "cpus" node we would
put the following in each cpu at N node:

scaling-method = "clock";

Or "psci" or "acpi" or whatever.

Thought exercise: for Hyperthreaded(tm) CPUs with 2 virtual cores for
every hard CPU (and multiple CPUs in a cluster):

scaling-method = "paired";

Or more simply, "hyperthreaded".
"""

Regards,
Mike

[1] http://www.spinics.net/lists/cpufreq/msg10034.html

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That being said, I don't really have any issue with such a function.
Some comments on the implementation.

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+static int of_property_match(const struct device_node *np1,
+                             const struct device_node *np2,
+                             const char *list_name)
+{
+       const __be32 *list1, *list2, *list1_end;

s/list/prop/

Everywhere.

Ok.

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+       int size1, size2;
+       phandle phandle1, phandle2;
+
+       /* Retrieve the list property */
+       list1 = of_get_property(np1, list_name, &size1);
+       if (!list1)
+               return -ENOENT;
+
+       list2 = of_get_property(np2, list_name, &size2);
+       if (!list2)
+               return -ENOENT;
+
+       if (size1 != size2)
+               return 0;
+
+       list1_end = list1 + size1 / sizeof(*list1);
+
+       /* Loop over the phandles */
+       while (list1 < list1_end) {
+               phandle1 = be32_to_cpup(list1++);
+               phandle2 = be32_to_cpup(list2++);
+
+               if (phandle1 != phandle2)
+                       return 0;
+       }

You can just do a memcmp here.

Yeah, that would be much better.

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This is wrong anyway because you don't know #clock-cells size.

I was actually comparing all the clock-cells, whatever there number
is to make sure "clocks" properties are exactly same. Anyway
memcmp will still guarantee that.

Thanks for your review.