linux-kernel - Re: [PATCH] thermal: step_wise: set throttle target within thermal instance limits

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Date:	Tue, 9 Apr 2013 10:09:34 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Eduardo Valentin <eduardo.valentin@...com>
Cc:	Zhang Rui <rui.zhang@...el.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thermal: step_wise: set throttle target within thermal
 instance limits

Hi Eduardo,

On Tue, Apr 9, 2013 at 8:00 AM, Eduardo Valentin
<eduardo.valentin@...com> wrote:
> Hi Andrew,
>
>
> On 08-04-2013 19:56, Andrew Bresticker wrote:
>>
>> When selecting a target cooling state in get_target_state(), make sure
>> that the state is at least as high as the minimum when the temperature
>> is rising and at least as low as the maximum when the temperature is
>> falling.  Previously the cooling level would only be incremented or
>> decremented by one in these cases.
>>
>> Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
>> ---
>>   drivers/thermal/step_wise.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
>> index 0cd5e9f..49992a4 100644
>> --- a/drivers/thermal/step_wise.c
>> +++ b/drivers/thermal/step_wise.c
>> @@ -47,9 +47,13 @@ static unsigned long get_target_state(struct
>> thermal_instance *instance,
>>         if (trend == THERMAL_TREND_RAISING) {
>>                 cur_state = cur_state < instance->upper ?
>>                             (cur_state + 1) : instance->upper;
>> +               if (cur_state < instance->lower)
>> +                       cur_state = instance->lower;
>>         } else if (trend == THERMAL_TREND_DROPPING) {
>>                 cur_state = cur_state > instance->lower ?
>>                             (cur_state - 1) : instance->lower;
>> +               if (cur_state > instance->upper)
>> +                       cur_state = instance->upper;
>>         }
>
>
>
> In which situations cur_state will be out of the [lower;upper] boundaries? I
> mean at this point while temperature is rising, and we are rising the
> cooling level, we should be already above lower (and vice-versa). Can you
> please describe better the situation you are trying to cover/ that you have
> identified?

Suppose we hit a trip point which has bounds from 5 to 10, but
cur_state is 0 because there has previously been no thermal
throttling.  In that case, we would only go to level 1, even though
the thermal instance specifies we should be between 5 and 10.  This
patch would fix it so that we go directly to level 5 instead.

I will resend this with a more descriptive commit message.

>
>>
>>         return cur_state;
>>
>

Thanks,
Andrew
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