linux-kernel - Re: [PATCH 4/6] thermal: add sanity check for the passive attribute

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Date:	Mon, 31 Aug 2009 16:33:50 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Frans Pop <elendil@...net.nl>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] thermal: add sanity check for the passive attribute

On Thu, 2009-08-27 at 00:48 +0800, Frans Pop wrote:
> On Wednesday 26 August 2009, Matthew Garrett wrote:
> > On Wed, Aug 26, 2009 at 06:17:23PM +0200, Frans Pop wrote:
> > > Values below 40000 milli-celsius (limit is somewhat arbitrary)
> > > don't make sense and can cause the system to go into a thermal
> > > heart attack: the actual temperature will always be lower and
> > > thus the system will be throttled down to its lowest setting.
> >
> > Not keen on this - it's a pretty arbitrary cutoff, and there are some
> > cases where someone might want this value. Policy belongs in userspace,
> > and all that.
> 
> What cases do you see? Testing? Or systems that might have to operate at 
> such a low temperature? I deliberately chose a value that's at a level 
> that's easy to reach.
> 
> I agree it is arbitrary, but it will prevent major confusion when someone 
> like me echo's 95 directly in sysfs.

this is a problem.
how about something like:
#define THERMAL_PASSIVE_WARNING_LEVEL 0x40000

if (state < THERMAL_PASSIVE_WARNING_LEVEL)
   printk(KERN_WARNING PREFIX "Passive trip point too low, this may"
          "slow down your laptop because processors are throttled "
          "whenever the temperature is higher than %dC\n", state/1000);

thanks,
rui

> Would 1000 (1 °C) perhaps be more acceptable as a limit? I doubt there are 
> valid use-cases for below 0 temps :-)

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