linux-kernel - Re: [RFC PATCH 02/11] ARM: DT/kernel: define ARM specific arch_of_get_cpu

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Date:	Tue, 16 Jul 2013 10:03:21 +0100
From:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
To:	Rob Herring <robherring2@...il.com>
CC:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"arnd@...db.de" <arnd@...db.de>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"rjw@...k.pl" <rjw@...k.pl>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"olof@...om.net" <olof@...om.net>,
	"gregory.clement@...e-electrons.com" 
	<gregory.clement@...e-electrons.com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>
Subject: Re: [RFC PATCH 02/11] ARM: DT/kernel: define ARM specific arch_of_get_cpu_node

On 15/07/13 20:10, Rob Herring wrote:
> On 07/15/2013 05:22 AM, Sudeep.KarkadaNagesha@....com wrote:
>> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@....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@....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

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