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

Eduardo Valentin
2014-10-02T21:13:43Z

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@samsung.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