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

From: Leo Yan <leo.yan@linaro.org>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
	edubezval@gmail.com, kevin.wangtao@linaro.org,
	vincent.guittot@linaro.org, amit.kachhap@gmail.com,
	linux-kernel@vger.kernel.org, javi.merino@kernel.org,
	rui.zhang@intel.com, daniel.thompson@linaro.org,
	linux-pm@vger.kernel.org
Subject: Re: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver
Date: Tue, 27 Mar 2018 11:43:44 +0800	[thread overview]
Message-ID: <20180327034344.GC21693@leoy-ThinkPad-X240s> (raw)
In-Reply-To: <faaf027c-e01c-6801-9a0c-ab7e0ba669a1@linaro.org>

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