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

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Date:	Tue, 7 Jan 2014 10:44:10 +0800
From:	Wei Ni <wni@...dia.com>
To:	Eduardo Valentin <eduardo.valentin@...com>,
	Mark Rutland <mark.rutland@....com>
CC:	Matthew Longnecker <MLongnecker@...dia.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 01/06/2014 10:54 PM, Eduardo Valentin wrote:
> * PGP Signed by an unknown key
> 
> 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.

Yes, I think so, but the of-thermal driver handle the
thermal_zone_device_register, and pass the "tzp" without governor_name,
so the created thermal_zone's governor will be NULL, then it can't run
into the governor->throttle() if needed. And currently there have no
interface to support updating governor and configuration at runtime.
I think it's better to initialize the governor_name when register the
thermal zone device in the of-thermal driver.

Thanks.

> 
>>
>> Thanks,
>> Mark.
>>
>>
> 
> 

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