linux-kernel - Re: [PATCH v5 2/4] devicetree: bindings: Document Krait CPU/L1 EDAC

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Date:	Tue, 25 Feb 2014 14:48:38 -0600
From:	Kumar Gala <galak@...eaurora.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	Mark Rutland <Mark.Rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 2/4] devicetree: bindings: Document Krait CPU/L1 EDAC


On Feb 25, 2014, at 5:16 AM, Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:

> Hi Stephen,
> 
> On Wed, Feb 19, 2014 at 12:20:43AM +0000, Stephen Boyd wrote:
>> (Sorry, this discussion stalled due to merge window + life events)
> 
> Sorry for the delay in replying on my side too.
> 
>> On 01/17, Lorenzo Pieralisi wrote:
>>> On Thu, Jan 16, 2014 at 07:26:17PM +0000, Stephen Boyd wrote:
>>>> On 01/16, Lorenzo Pieralisi wrote:
>>>>> On Thu, Jan 16, 2014 at 06:05:05PM +0000, Stephen Boyd wrote:
>>>>>> On 01/16, Lorenzo Pieralisi wrote:
>>>>>>> Do we really want to do that ? I am not sure. A cpus node is supposed to
>>>>>>> be a container node, we should not define this binding just because we
>>>>>>> know the kernel creates a platform device for it then.
>>>>>> 
>>>>>> This is just copying more of the ePAPR spec into this document.
>>>>>> It just so happens that having a compatible field here allows a
>>>>>> platform device to be created. I don't see why that's a problem.
>>>>> 
>>>>> I do not see why you cannot define a node like pmu or arch-timer and stick
>>>>> a compatible property in there. cpus node does not represent a device, and
>>>>> must not be created as a platform device, that's my opinion.
>>>>> 
>>>> 
>>>> I had what you're suggesting before in the original revision of
>>>> this patch. Please take a look at the original patch series[1]. I
>>>> suppose it could be tweaked slightly to still have a cache node
>>>> for the L2 interrupt and the next-level-cache pointer from the
>>>> CPUs.
>>> 
>>> Ok, sorry, we are running around in circles here, basically you moved
>>> the node to cpus according to reviews. I still think that treating cpus
>>> as a device is not a great idea, even though I am in the same
>>> position with C-states and probably will add C-state tables in the cpus
>>> node.
>>> 
>>> http://comments.gmane.org/gmane.linux.power-management.general/41012
>>> 
>>> I just would like to see under cpus nodes and properties that apply to
>>> all ARM systems, and avoid defining properties (eg interrupts) that
>>> have different meanings for different ARM cores.
>>> 
>>> The question related to why the kernel should create a platform device
>>> out of cpus is still open. I really do not want to block your series
>>> for these simple issues but we have to make a decision and stick to that,
>>> I am fine either way if we have a plan.
>>> 
>> 
>> Do you just want a backup plan in case we don't make a platform
>> device out of the cpus node? I believe we can always add code
>> somewhere to create a platform device at runtime if we detect the
>> cpus node has a compatible string equal to "qcom,krait". We could
>> probably change this driver's module_init() to scan the DT for
>> such a compatible string and create the platform device right
>> there. If we get more than one interrupt in the cpus node we can
>> add interrupt-names and then have software look for interrupts by
>> name instead of number.
> 
> As I mentioned, I do not like the idea of adding compatible properties
> just to force the kernel to create platform devices out of device tree
> nodes. On top of that I would avoid adding a compatible property
> to the cpus node (after all properties like enable-method are common for all
> cpus but still duplicated), my only concern being backward compatibility
> here (ie if we do that for interrupts, we should do that also for other
> common cpu nodes properties, otherwise we have different rules for
> different properties).
> 
> I think you can then add interrupts to cpu nodes ("qcom,krait" specific),
> and as you mentioned create a platform device for that.
> 
> Thanks,
> Lorenzo

So I agree with the statement about adding compatibles just to create platform devices is wrong.  However its seems perfectly reasonable for a cpu node to have a compatible property.  I don’t see why a CPU is any different from any other device described in a DT.

- k

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation

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