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

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Message-ID: <20140107120248.GD4180@e106331-lin.cambridge.arm.com>
Date:	Tue, 7 Jan 2014 12:02:48 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Wei Ni <wni@...dia.com>
Cc:	Eduardo Valentin <eduardo.valentin@...com>,
	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 Tue, Jan 07, 2014 at 02:44:10AM +0000, Wei Ni wrote:
> 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.

Initialising it in the driver doesn't mean it has to come from the
device tree. That's still a run-time decision, even though it's made
immediately after parsing the DT.

Thanks,
Mark.
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