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

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Message-ID: <20180327034344.GC21693@leoy-ThinkPad-X240s>
Date:   Tue, 27 Mar 2018 11:43:44 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...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 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?

Thanks,
Leo Yan