linux-kernel - Re: Re: [PATCH v4 2/3] devfreq: Add suspend and resume apis

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Message-id: <12788576.101631350369619343.JavaMail.weblogic@epml27>
Date:	Tue, 16 Oct 2012 06:40:22 +0000 (GMT)
From:	MyungJoo Ham <myungjoo.ham@...sung.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Rajagopal Venkat <rajagopal.venkat@...aro.org>,
	"mturquette@...aro.org" <mturquette@...aro.org>,
	박경민 <kyungmin.park@...sung.com>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	이종화 <jonghwa3.lee@...sung.com>
Subject: Re: Re: [PATCH v4 2/3] devfreq: Add suspend and resume apis

> On Monday 08 of October 2012 10:48:24 MyungJoo Ham wrote:
> > > On 8 October 2012 03:31, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > > On Thursday 04 of October 2012 14:58:33 Rajagopal Venkat wrote:
> > > >> Add devfreq suspend/resume apis for devfreq users. This patch
> > > >> supports suspend and resume of devfreq load monitoring, required
> > > >> for devices which can idle.
> > > >>
> > > >> Signed-off-by: Rajagopal Venkat <rajagopal.venkat@...aro.org>
> > > >> Acked-by: MyungJoo Ham <myungjoo.ham@...sung.com>
> > > >
> > > > Well, I wonder if this may be tied in to the runtime PM framework, so that,
> > > > for example, pm_runtime_suspend() will automatically suspend devfreq on
> > > > success (and the runtime resume of the device will resume devfreq)?
> > > 
> > > That's a good idea. If you agree, we can handle this as separate patch on
> > > top this patchset.
> 
> Sure.
> 
> > I guess implementing the idea may be not so obvious; thus, seperating
> > the patchset would be appropriate.
> > 
> > When we implement the idea, we may need to implement at the
> > pm_runtime core. Because devfreq->dev is a child of the target dev, not
> > a parent, runtime-pm event of the target dev does not automatically
> > invoke a cascaded action on the devfreq->dev.
> 
> I'm not exactly sure what you mean, care to explain?

When a device "p" creates devfreq, devfreq->dev->parent = p.
And, devfreq's functions need to react to the "p"'s runtime-pm events.

However, when "p"'s runtime-pm-suspend is being invoked,
devfreq->dev's runtime-pm-suspend won't be automatically invoked.

Thus, we will need a mechanism that invokes devfreq->dev's runtime-pm
callbacks when p's runtime-pm is invoked. (at the runtime-pm core)
Or
A mechanism that one can notify others (including its children) when
the one's runtime-pm is invoked. (probably at the runtime-pm core, too)

Without such support, it appears that the current implementation
(calling runtime-pm suspend/resume equivalent devfreq functions
manually at device drivers) seems to be inevitable.



Anyway, if devfreq->dev is a parent of "p", runtime-pm core will
do the required task automatically; however, it isn't and I don't
think it'd be appropriate.

> 
> > Maybe either
> > 1) capability to allow a child to monitor the power state of a parent
> > (I remember Inki Dae once suggested to add notifiers at runtime-pm, but
> > it seems to be not merged)
> > or
> > 2) letting runtime-pm be aware of devfreq
> > (doesn't feel alright with this??)
> > is required?
> 
> I'm not a big fan of notifiers, so I'd prefer to avoid using them, if
> possible.
> 
> Thanks,
> Rafael
> 
> 
> -- 
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
> 

Cheers,
MyungJoo