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

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Date:	Wed, 17 Jul 2013 15:16:54 +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 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@....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.

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

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