linux-kernel - Re: [PATCH 1/3] thermal: step_wise: fix: Prevent from binary overflow when trend is dropping

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Message-ID: <20141002211325.GA5016@developer>
Date:	Thu, 2 Oct 2014 17:13:31 -0400
From:	Eduardo Valentin <edubezval@...il.com>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	Zhang Rui <rui.zhang@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] thermal: step_wise: fix: Prevent from binary
 overflow when trend is dropping

Hello Lukasz,

On Wed, Sep 24, 2014 at 10:27:10AM +0200, Lukasz Majewski wrote:
> It turns out that some boards can have instance->lower greater than 0 and
> when thermal trend is dropping it results with next_target equal to -1.
> 
> Since the next_target is defined as unsigned long it is interpreted as
> 0xFFFFFFFF and larger than instance->upper.
> As a result the next_target is set to instance->upper which ramps up to
> maximal cooling device target when the temperature is steadily decreasing.
> 

Thanks for finding a problem and sending a fix.

Can you please explain a little more on how next_target reaches -1 when
lower is greater than 0?


> Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> ---
>  drivers/thermal/step_wise.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
> index 3b54c2c..fdd1f52 100644
> --- a/drivers/thermal/step_wise.c
> +++ b/drivers/thermal/step_wise.c
> @@ -77,7 +77,7 @@ static unsigned long get_target_state(struct thermal_instance *instance,
>  			next_target = instance->upper;
>  		break;
>  	case THERMAL_TREND_DROPPING:
> -		if (cur_state == instance->lower) {
> +		if (cur_state <= instance->lower) {
>  			if (!throttle)
>  				next_target = THERMAL_NO_TARGET;
>  		} else {
> -- 
> 2.0.0.rc2
> 


Eduardo
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