Message-ID: <51E98A07.4050402@wwwdotorg.org>
Date: Fri, 19 Jul 2013 12:48:39 -0600
From: Stephen Warren <swarren@wwwdotorg.org>
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To: Guenter Roeck <linux@roeck-us.net>
CC: Eduardo Valentin <eduardo.valentin@ti.com>,
        Grant Likely <grant.likely@linaro.org>,
        Rob Herring <rob.herring@calxeda.com>,
        devicetree-discuss@lists.ozlabs.org, wni@nvidia.com,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        lm-sensors@lm-sensors.org, l.stach@pengutronix.de
Subject: Re: [lm-sensors] [RESEND PATCH V1 0/9] thermal: introduce DT thermal
 zone build
References: <1374074248-31690-1-git-send-email-eduardo.valentin@ti.com> <20130717220942.GB990@roeck-us.net> <51E7F341.8020508@ti.com> <51E8234D.1020607@wwwdotorg.org> <20130718212108.GC4110@roeck-us.net>
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On 07/18/2013 03:21 PM, Guenter Roeck wrote:
> On Thu, Jul 18, 2013 at 11:18:05AM -0600, Stephen Warren wrote:
>> On 07/18/2013 07:53 AM, Eduardo Valentin wrote:
>>> Hello Guenter,
>>>
>>> On 17-07-2013 18:09, Guenter Roeck wrote:
>>>> On Wed, Jul 17, 2013 at 11:17:19AM -0400, Eduardo Valentin
>>>> wrote:
>>>>> Hello all,
>>>>>
>>>>> As you noticed, I am working in a way to represent thermal
>>>>> data using device tree [1]. Essentially, this should be a way
>>>>> to say what to do with a sensor and how to associate (cooling)
>>>>> actions with it.
>>>>>
>>>> Seems to me that goes way beyond the supposed scope of devicetree
>>>> data. Devicetree data is supposed to describe hardware, not its
>>>> configuration or use. This is clearly a use case.
>>>
>>> Thanks for rising your voice here. It is important to know what
>>> hwmon ppl think about this.
>>
>> I meant to find time to read Guenter's original email where he
>> initially objected to putting data into DT, and determine exactly what
>> was being objected to. I still haven't:-( However, the arguments that
>> Eduardo stated in his email do make sense to me; I agree that
>> temperature limits really are a description of HW. Details of which
>> cooling methods to invoke when certain temperature limits are reached
>> is also part of the HW/system design, and hence I would tend to agree
>> that they're appropriate to include in DT. Anyway, that's just my 2
>> cents on the matter:-)
> 
> Many systems have multiple profiles for various use cases (high performance,
> low power etc), and limits are different based on the use case. If that means
> you are going to have multiple devicetree variants based on the profile,
> I would argue that you crossed the line.

Yes, I can see that argument. However, a counter-point:

* I believe we do need a DT binding to describe the absolute thermal
limits of a system, for safety/correctness of system operation.

* We need to define a syntax/schema to represent that.

* If we then want to implement additional profiles with stricter limits,
do we really want to invent a different syntax/schema to represent
those? Representing them in the same way seems like good use of the
design, mind-share, etc.

* Perhaps that doesn't mean that the additional profiles have to be in
DT though; just that we somehow make any other representation of those
profiles as close to the DT representation in syntax/structure as we
can, to get maximum re-use.

> With thermal profiles it gets even more
> complicated, as those parameters may be played around with and changed
> multiple times to find the best settings to achieve optimal cooling.

To me, that sounds more like fixing a bug in the initial data, rather
than something which fundamentally affects how the data should be
represented.

> Does this describe hardware ? I don't think so, but, as I mentioned before,
> maybe I am wrong.

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