Re: [PATCH] ARM: dts: specify all the per-cpu interrupts of arch timer for exynos5440

From: Santosh Shilimkar <santosh.shilimkar-l0cyMroinI0@public.gmane.org>
To: Benoit Cousson <b-cousson-l0cyMroinI0@public.gmane.org>,
	Marc Zyngier <marc.zyngier-5wv7dgnIgG8@public.gmane.org>
Cc: "linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org"
	<devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org>,
	"rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org"
	<rob.herring-bsGFqQB8/DxBDgjK7y7TUQ@public.gmane.org>,
	Kukjin Kim <kgene.kim-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
	'Thomas Abraham'
	<thomas.ab-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>,
	"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
	<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [PATCH] ARM: dts: specify all the per-cpu interrupts of arch timer for exynos5440
Date: Thu, 24 Jan 2013 18:23:21 +0530	[thread overview]
Message-ID: <51012EC1.6010803@ti.com> (raw)
In-Reply-To: <51012C4B.5080300-l0cyMroinI0@public.gmane.org>

On Thursday 24 January 2013 06:12 PM, Benoit Cousson wrote:
> Hi Santosh,
>
> On 01/23/2013 11:55 AM, Santosh Shilimkar wrote:
>> Looping Marc, Benoit
>>
>> On Wednesday 23 January 2013 04:06 PM, Mark Rutland wrote:
>>> On Tue, Jan 22, 2013 at 10:05:18PM +0000, Kukjin Kim wrote:
>>>> Mark Rutland wrote:
>>>>>
>>>> + devicetree-discuss, Grant Likely, Rob Herring and Tony Lindgren
>>>>
>>>>> On Tue, Jan 22, 2013 at 01:41:27AM +0000, Kukjin Kim wrote:
>>>>>> From: Thomas Abraham <thomas.ab-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
>>>>>>
>>>>>> Need to be changed requirements in the 'cpus' node for exynos5440
>>>>>> to specify all the per-cpu interrupts of arch timer.
>>>>>
>>>>> The node(s) for the arch timer should not be in the cpus/cpu@N nodes.
>>>>> Instead, there should be one node (in the root of the tree).
>>>>>
>>>> Well, I don't think so. As per my understanding, the local timers are
>>>> attached to every ARM cores (cpus) and it generates certain interrupt
>>>> to the
>>>> GIC. So the correct representation for this in device tree is to
>>>> include the
>>>> interrupts in the cpu nodes in dts file. Your comments  refer to a
>>>> limitation in the Linux kernel implementation of the arch_timer and it
>>>> should not result in representing the hardware details incorrectly in
>>>> the
>>>> dts file.
>>>
>>> I disagree. The "correct representation" is whatever the devicetree
>>> binding
>>> documentation describes. It does not describe placing timer nodes in
>>> the cpu
>>> nodes.
>>>
>> This seems to be exact same topic what is getting discussed here [1]
>> Technically DT is suppose to represent how the hardware is rather than
>> how the bindings are done.
>>
>> But as Marc pointed out, the approach taken currently is to not
>> duplicate the banked information. The thread [1] isn't concluded
>> yet but looks like we might want to avoid duplicating the information
>> considering, more of such duplication needs to follow. e.g gic i/f
>>
>> Am still waiting on what Benoit has to say ?
>
> I agree with you :-)
>
> I'm not sure the binding was properly done to reflect the HW accurately.
>
> A local timer for my point of view should be located in the cpu node
> like a L1 cache. Or at least referenced in each cpu by a phandle.
>
> What was the rational to put it in the root?
>
 From Marc's answer it seems to avoid the duplication of data but
I let him elaborate it.

Regards,
Santosh