linux-kernel - Re: [PATCH] thermal: Fix KELVIN_TO

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Date:	Thu, 03 Apr 2014 10:40:41 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Joe Perches <joe@...ches.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Eduardo Valentin <eduardo.valentin@...com>
Subject: Re: [PATCH] thermal: Fix KELVIN_TO_CELSIUS macro

On Sun, 2014-03-23 at 22:30 -0700, Guenter Roeck wrote:
> On 03/23/2014 09:25 PM, Joe Perches wrote:
> > On Sun, 2014-03-23 at 21:14 -0700, Guenter Roeck wrote:
> >> It is always a good idea to use paranthesis around macro parameters
> >> to avoid undesired side effects.
> >>
> >> In this specific case, KELVIN_TO_CELSIUS() is used in
> >> drivers/platform/x86/asus-wmi.c with parameter "value & 0xFFFF",
> >> which due to operator evaluation order causes more or less random
> >> results.
> >
> > Maybe it's better to use a statement expression to avoid
> > multiple calculations of t
> >
> > Maybe;
> >
> > #define KELVIN_TO_CELSIUS(t)				\
> > ({							\
> > 	long _t = (long)(t) - 2732;			\
> > 	_t >= 0 ? (_t + 5) / 10 : (_t - 5) / 10;	\
> > })
> >
> >
> 
> Possibly, but I only want to have a bug fixed which should possibly be applied
> to -stable at some point. As such, I prefer the minimalistic approach.
> Anything more fancy on top of that can be submitted as separate patch.
> 
I agreed. I will take this patch and push it for stable kernel.

thanks,
rui

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