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

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

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.

Let me know how would you prefer me to proceed on this.

Regards,
Sudeep