linux-kernel - Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver

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Date:   Tue, 27 Mar 2018 13:10:07 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>, edubezval@...il.com,
        kevin.wangtao@...aro.org, vincent.guittot@...aro.org,
        amit.kachhap@...il.com, linux-kernel@...r.kernel.org,
        javi.merino@...nel.org, rui.zhang@...el.com,
        daniel.thompson@...aro.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu
 idle cooling driver

On 27/03/2018 05:43, Leo Yan wrote:
> On Fri, Feb 23, 2018 at 12:28:51PM +0100, Daniel Lezcano wrote:
>> On 23/02/2018 08:34, Viresh Kumar wrote:
>>> On 21-02-18, 16:29, Daniel Lezcano wrote:
> 
>> [ ... ]
>>
>>>> +static s64 cpuidle_cooling_runtime(struct cpuidle_cooling_device *idle_cdev)
>>>> +{
>>>> +	s64 next_wakeup;
>>>> +	int state = idle_cdev->state;
>>>> +
>>>> +	/*
>>>> +	 * The function must never be called when there is no
>>>> +	 * mitigation because:
>>>> +	 * - that does not make sense
>>>> +	 * - we end up with a division by zero
>>>> +	 */
>>>> +	BUG_ON(!state);
>>>
>>> As there is no locking in place, we can surely hit this case. What if
>>> the state changed to 0 right before this routine was called ?
>>>
>>> I would suggest we should just return 0 in that case and get away with
>>> the BUG_ON().
> 
> Here if 'state' equals to 0 and we return 0, then the return value will
> be same with when 'state' = 100; this lets the return value confused.
> 
> I think for 'state' = 0, should we return -1 so indicate the hrtimer
> will not be set for this case?

Yeah, I will look at how to make this smoother.

Thanks

  -- Daniel


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