linux-kernel - Re: [PATCHv9 02/20] thermal: introduce device tree parser

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Date:	Mon, 6 Jan 2014 10:54:39 -0400
From:	Eduardo Valentin <eduardo.valentin@...com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Matthew Longnecker <mlongnecker@...dia.com>,
	Wei Ni <wni@...dia.com>,
	Eduardo Valentin <eduardo.valentin@...com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	Pawel Moll <Pawel.Moll@....com>,
	"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux@...ck-us.net" <linux@...ck-us.net>,
	"rui.zhang@...el.com" <rui.zhang@...el.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"durgadoss.r@...el.com" <durgadoss.r@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv9 02/20] thermal: introduce device tree parser

On 06-01-2014 09:51, Mark Rutland wrote:
> On Thu, Jan 02, 2014 at 05:50:06PM +0000, Matthew Longnecker wrote:
>>
>>> I think the platform driver may set governor for the thermal zone,
>>> so how about to add a property named as "governor",
>>> and parse it to tzp->governor_name,
>>> something like:
>>>                  ret = of_property_read_string(child, "governor", &str);
>>>                  if (ret == 0)
>>>                          if (strlen(str) < THERMAL_NAME_LENGTH)
>>>                                  strcpy(tzp->governor_name, str);
>>>
>>> Thanks.
>>> Wei.
>>
>> DT is supposed to describe the hardware, right? The governor isn't 
>> hardware -- it's a software control policy. On the other hand, that 
>> control policy must be tuned according to the behaviors of the platform 
>> hardware otherwise the system will be unstable.
>>
>> Is it appropriate to be naming the governor in DT? If so, is it equally 
>> appropriate to describe any governor-specific parameters in DT (even 
>> though they are pure software constructs)?
> 
> The dt should be relatively static -- if the hardware doesn't change the
> dt shouldn't have to.
> 
> The governers are not static. We can introduce new ones and throw away
> old ones at any time. Tuning parameters can also change at any time.
> 
> I'd prefer to not have governer details described in the dt, and the
> choice of governer and configuration of its tuning parameters should be
> made at runtime somehow.

Agreed.

> 
> Thanks,
> Mark.
> 
> 


-- 
You have got to be excited about what you are doing. (L. Lamport)

Eduardo Valentin


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