linux-kernel - RE: [PATCH 1/4] thermal: Add new thermal trend type to support quick cooling

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Date:	Mon, 12 Nov 2012 07:31:27 +0000
From:	"R, Durgadoss" <durgadoss.r@...el.com>
To:	"Zhang, Rui" <rui.zhang@...el.com>
CC:	Amit Kachhap <amit.kachhap@...aro.org>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"jonghwa3.lee@...sung.com" <jonghwa3.lee@...sung.com>
Subject: RE: [PATCH 1/4] thermal: Add new thermal trend type to support
 quick cooling



> -----Original Message-----
> From: Zhang, Rui
> Sent: Monday, November 12, 2012 12:03 PM
> To: R, Durgadoss
> Cc: Amit Kachhap; linux-pm@...ts.linux-foundation.org; linux-samsung-
> soc@...r.kernel.org; linux-kernel@...r.kernel.org; lenb@...nel.org; linux-
> acpi@...r.kernel.org; jonghwa3.lee@...sung.com
> Subject: RE: [PATCH 1/4] thermal: Add new thermal trend type to support
> quick cooling
> 
> On Sun, 2012-11-11 at 22:55 -0700, R, Durgadoss wrote:
> > Hi Amit/Rui,
> >
> > > -----Original Message-----
> > > From: Amit Kachhap [mailto:amit.kachhap@...aro.org]
> > > Sent: Friday, November 09, 2012 11:52 AM
> > > To: Zhang, Rui
> > > Cc: linux-pm@...ts.linux-foundation.org; linux-samsung-
> > > soc@...r.kernel.org; linux-kernel@...r.kernel.org; R, Durgadoss;
> > > lenb@...nel.org; linux-acpi@...r.kernel.org;
> jonghwa3.lee@...sung.com
> > > Subject: Re: [PATCH 1/4] thermal: Add new thermal trend type to
> support
> > > quick cooling
> > >
> > > On 9 November 2012 09:21, Zhang Rui <rui.zhang@...el.com> wrote:
> > > > On Thu, 2012-11-08 at 11:56 +0530, Amit Kachhap wrote:
> > > >> On 8 November 2012 11:31, Zhang Rui <rui.zhang@...el.com> wrote:
> > > >> > On Thu, 2012-11-08 at 09:56 +0530, Amit Daniel Kachhap wrote:
> > > >> >> This modification adds 2 new thermal trend type
> > > THERMAL_TREND_RAISE_FULL
> > > >> >> and THERMAL_TREND_DROP_FULL. This thermal trend can be used
> to
> > > quickly
> > > >> >> jump to the upper or lower cooling level instead of incremental
> > > increase
> > > >> >> or decrease.
> > > >> >
> > > >> > IMO, what we need is a new more aggressive cooling governor
> which
> > > always
> > > >> > uses upper limit when the temperature is raising and lower limit
> when
> > > >> > the temperature is dropping.
> > > >> Yes I agree that a new aggressive governor is the best approach but
> > > >> then i thought adding a new trend type is a simple solution to achieve
> > > >> this and since most of the governor logic might be same as the
> > > >> step-wise governor. I have no objection in doing it through governor.
> > > >> >
> > > > hmmm,
> > > > I think a more proper way is to set the cooling state to upper limit
> > > > when it overheats and reduce the cooling state step by step when the
> > > > temperature drops.
> > >
> > > No actually I was thinking of having a  simple governor with a feature
> > > like it only sets to upper level and lower level. Also since the
> > > temperature sensor is capable of interrupting for both increase in
> > > threshold(say 100C)  and fall in threshold (say 90C), so polling or
> > > step increments is not needed at all.
> > > Currently stepwise governor governor does that so we might change the
> > > macro name as,
> > > THERMAL_TREND_RAISE_STEP,
> > > THERMAL_TREND_DROP_STEP,
> > > THERMAL_TREND_RAISE_MAX,
> > > THERMAL_TREND_DROP_MAX,
> > >
> > > and file step_wise.c can be named as state_wise.c or trend_wise.c.
> >
> > Yes, in this particular case, we neither need to poll nor do step wise
> > operations. But, most of the other sensors need at least one of them.
> >
> > So, I think we can try it this way:
> > 	if (sensor supports interrupt) {
> > 		'always' use RAISE_MAX and DROP_MAX;
> > 	} else {
> > 		Do Step wise operations
> > 	}
> >
> why should the generic thermal layer be aware of this?
> 
> IMO, it is the platform thermal driver that is responsible for returning
> THERMAL_TREND_RAISE_STEP or THERMAL_TREND_RAISE_MAX.
> 
> and the step_wise governor just takes action based on the return value
> of .get_trend() callback.

Yes, agree with the flow ..

Thanks,
Durga