linux-kernel - Re: [RFC PATCH v2 3/4] powerpc: refactor of_get_cpu

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Message-ID: <521223FA.5050903@arm.com>
Date:	Mon, 19 Aug 2013 14:56:10 +0100
From:	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>
To:	Rob Herring <robherring2@...il.com>
CC:	Mark Rutland <Mark.Rutland@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jonas Bonn <jonas@...thpole.se>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Michal Simek <monstr@...str.eu>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Sudeep KarkadaNagesha <Sudeep.KarkadaNagesha@....com>,
	Tomasz Figa <tomasz.figa@...il.com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>
Subject: Re: [RFC PATCH v2 3/4] powerpc: refactor of_get_cpu_node to support
 other architectures

On 19/08/13 14:02, Rob Herring wrote:
> On 08/19/2013 05:19 AM, Mark Rutland wrote:
>> On Sat, Aug 17, 2013 at 11:09:36PM +0100, Benjamin Herrenschmidt wrote:
>>> On Sat, 2013-08-17 at 12:50 +0200, Tomasz Figa wrote:
>>>> I wonder how would this handle uniprocessor ARM (pre-v7) cores, for
>>>> which 
>>>> the updated bindings[1] define #address-cells = <0> and so no reg 
>>>> property.
>>>>
>>>> [1] - http://thread.gmane.org/gmane.linux.ports.arm.kernel/260795
>>>
>>> Why did you do that in the binding ? That sounds like looking to create
>>> problems ... 
>>>
>>> Traditionally, UP setups just used "0" as the "reg" property on other
>>> architectures, why do differently ?
>>
>> The decision was taken because we defined our reg property to refer to
>> the MPIDR register's Aff{2,1,0} bitfields, and on UP cores before v7
>> there's no MPIDR register at all. Given there can only be a single CPU
>> in that case, describing a register that wasn't present didn't seem
>> necessary or helpful.
> 
> What exactly reg represents is up to the binding definition, but it
> still should be present IMO. I don't see any issue with it being
> different for pre-v7.
> 
Yes it's better to have 'reg' with value 0 than not having it.
Otherwise this generic of_get_cpu_node implementation would need some
_hack_ to handle that case.

Regards,
Sudeep


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