linux-kernel - Re: [RFC PATCH] PM / devfreq: Add policy notifier

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Date:   Thu, 17 May 2018 16:07:28 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Chanwoo Choi <cw00.choi@...sung.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Brian Norris <briannorris@...omium.org>
Subject: Re: [RFC PATCH] PM / devfreq: Add policy notifier

Hi,

On Thu, May 17, 2018 at 11:01:34AM +0900, Chanwoo Choi wrote:
> Hi,
> 
> Could you give some use-case of DEVFREQ_POLICY_NOTIFIER
> or send use-case patch with this patch?

This is a WIP patch that makes use of the DEVFREQ_POLICY_NOTIFIER:

https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1065122

> I already knew the CPUFREQ_POLICY_NOTIFIER.
> But, until now, there are no any requirements of DEVFREQ_POLICY_NOTIFIER.
> If there are no any use-case, it is not necessary codes.

Sure, I intend to land the above driver upstream if devfreq can
provide the necessary interfaces.

> On 2018년 05월 16일 06:24, Matthias Kaehlcke wrote:
> > diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> > index fe2af6aa88fc..a7294c056f65 100644
> > --- a/drivers/devfreq/devfreq.c
> > +++ b/drivers/devfreq/devfreq.c
> > @@ -273,6 +273,9 @@ int update_devfreq(struct devfreq *devfreq)
> >  	if (err)
> >  		return err;
> >  
> > +	srcu_notifier_call_chain(&devfreq->policy_notifier_list,
> > +			DEVFREQ_ADJUST, &freq);
> 
> It is not proper to used 'freq' as the passed data.
> In current step,'freq' is not adjusted and is not final decided
> frequency.

Right, the next revision will pass a struct devfreq_policy instead,
where the notifiers can adjust the min/max values, similar to what
cpufreq does.

Thanks

Matthias