Re: [RFC PATCH 02/11] ARM: DT/kernel: define ARM specific arch_of_get_cpu_node

[Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@arm.com>]

On 16/07/13 10:03, Sudeep KarkadaNagesha wrote:
> On 15/07/13 20:10, Rob Herring wrote:
>> On 07/15/2013 05:22 AM, Sudeep.KarkadaNagesha@arm.com wrote:
>>> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
>>>
>>> CPU subsystem now provides architecture specific hook to retrieve the
>>> of_node. Most of the cpu DT node parsing and initialisation is contained
>>> in devtree.c. It's better to contain all CPU device node parsing there.
>>>
>>> arch_of_get_cpu_node is mainly used to assign cpu->of_node when CPUs get
>>> registered. This patch overrides the defination of the same. It can also
>>> act as the helper function in pre-SMP/early initialisation stages to
>>> retrieve CPU device node pointers in logical ordering.
>>>
>>> This mainly helps to avoid replication of the code doing CPU node parsing
>>> and physical(MPIDR) to logical mapping.
>>>
>>> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
>>
>> [snip]
>>
>>> +struct device_node * __init arch_of_get_cpu_node(int cpu)
>>> +{
>>> +	struct device_node *cpun, *cpus;
>>> +	const u32 *cell;
>>> +	u64 hwid;
>>> +	int ac;
>>> +
>>> +	cpus = of_find_node_by_path("/cpus");
>>> +	if (WARN(!cpus, "Missing cpus node, bailing out\n"))
>>> +		return NULL;
>>> +
>>> +	if (WARN_ON(of_property_read_u32(cpus, "#address-cells", &ac)))
>>> +		ac = of_n_addr_cells(cpus);
>>> +
>>> +	for_each_child_of_node(cpus, cpun) {
>>> +		if (of_node_cmp(cpun->type, "cpu"))
>>> +			continue;
>>> +		cell = of_get_property(cpun, "reg", NULL);
>>> +		if (WARN(!cell, "%s: missing reg property\n", cpun->full_name))
>>> +			continue;
>>> +
>>> +		hwid = of_read_number(cell, ac);
>>> +		if ((hwid & MPIDR_HWID_BITMASK) == cpu_logical_map(cpu))
>>
>> Most of this function is not ARM specific, so it would be nice if we
>> could shrink the arch specific part down to just this match. A default
>> match of reg == logical cpu number might be useful.
>>
> I completely agree, in fact that was my initial idea too.
> 
> But when I had a look at powerpc implementation of "of_get_cpu_node" in
> arch/powerpc/kernel/prom.c, it looked like PPC is using some
> compatibles(e.g. ibm,ppc-interrupt-server#s) which are not specified in
> ePAPR. I am not sure is that's allowed or not, if allowed then we can't
> have generic of_get_cpu_node with just arch specific hwid matching function.

I meant property names not compatibles. Looks like PPC and SPARC seem to
use non-standard property names like "cpuid",
"ibm,ppc-interrupt-server#s" instead of single "reg" property for all
cpus/threads

Since the cpufreq driver doesn't depend on those properties, I moved
arch_of_get_cpu_node to OF/DT core in v2.

Regards,
Sudeep