linux-kernel - Re: Re: [PATCHv4 1/8] devfreq: event: Add new devfreq_event class to provide basic data for devfreq governor

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Date:	Fri, 19 Dec 2014 02:11:31 +0000 (GMT)
From:	MyungJoo Ham <myungjoo.ham@...sung.com>
To:	최찬우 <cw00.choi@...sung.com>
Cc:	김국진 <kgene.kim@...sung.com>,
	박경민 <kyungmin.park@...sung.com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	ABHILASH KESAVAN <a.kesavan@...sung.com>,
	"tomasz.figa@...il.com" <tomasz.figa@...il.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	대인기 <inki.dae@...sung.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>
Subject: Re: Re: [PATCHv4 1/8] devfreq: event: Add new devfreq_event class to
 provide basic data for devfreq governor

>   
>  Dear Myungjoo,
> 
> Thanks for your review.
> 
> On 12/18/2014 03:24 PM, MyungJoo Ham wrote:
> > Hi Chanwoo,
> > 
> > I love the idea and I now have a little mechanical issues in your code.
> > 
> >> ---
> >>  drivers/devfreq/Kconfig         |   2 +
> >>  drivers/devfreq/Makefile        |   5 +-
> >>  drivers/devfreq/devfreq-event.c | 449 ++++++++++++++++++++++++++++++++++++++++
> >>  drivers/devfreq/event/Makefile  |   1 +
> >>  include/linux/devfreq.h         | 160 ++++++++++++++
> >>  5 files changed, 616 insertions(+), 1 deletion(-)
> >>  create mode 100644 drivers/devfreq/devfreq-event.c
> >>  create mode 100644 drivers/devfreq/event/Makefile
> >>

[]

> 
> > 
> > 
> > [snip]
> > 
> >> diff --git a/drivers/devfreq/devfreq-event.c b/drivers/devfreq/devfreq-event.c
> >> new file mode 100644
> >> index 0000000..0e1948e
> >> --- /dev/null
> >> +++ b/drivers/devfreq/devfreq-event.c
> >> @@ -0,0 +1,449 @@
> >> +/*
> >> + * devfreq-event: Generic DEVFREQ Event class driver
> > 
> > DEVFREQ is a generic DVFS mechanism (or subsystem).
> > 
> > Plus, I thought devfreq-event is considered to be a "framework"
> > for devfreq event class drivers. Am I mistaken?
> 
> You're right. just "class driver" description is not proper.
> I'll modify the description of devfreq-event.c as following:
> or If you have other opinion, would you please let me know about it?
> 
> 	devfreq-event: DEVFREQ-Event Framework to provide raw data of Non-CPU Devices.

devfreq-event: a framework to provide raw data and events of devfreq devices

should be enough.


[]
> > [snip / reversed maybe.. sorry]
> > 
> >> +/**
> >> + * devfreq_event_is_enabled() - Check whether devfreq-event dev is enabled or
> >> + *                             not.
> >> + * @edev       : the devfreq-event device
> >> + *
> >> + * Note that this function check whether devfreq-event dev is enabled or not.
> >> + * If return true, the devfreq-event dev is enabeld. If return false, the
> >> + * devfreq-event dev is disabled.
> >> + */
> >> +bool devfreq_event_is_enabled(struct devfreq_event_dev *edev)
> >> +{
> >> +       bool enabled = false;
> >> +
> >> +       if (!edev || !edev->desc)
> >> +               return enabled;
> >> +
> >> +       mutex_lock(&edev->lock);
> >> +
> >> +       if (edev->enable_count > 0)
> >> +               enabled = true;
> >> +
> >> +       if (edev->desc->ops && edev->desc->ops->is_enabled)
> >> +               enabled |= edev->desc->ops->is_enabled(edev);
> > 
> > What does it mean when enabled_count > 0 and ops->is_enabled() is false? or..
> > What does it mean when enabled_count = 0 and ops->is_enabled() is true?
> > 
> > If you do enable_count in the subsystem, why would we rely on
> > ops->is_enabled()? Are you assuming that a device MAY turn itself off
> > without any kernel control (ops->disable()) and it is still a correct
> > behabior?
> 
> You're right. devfreq_event_is_enabled() has ambiguous operation according to your comment.
> 
> I'll only control the enable_count in the subsystem without ops->is_enabled()
> and then remove the is_enabled function in the structre devfreq_event_ops.
> 
> Best Regards,
> Chanwoo Choi
> 

[Off-Topic]

The name of devfreq-event may look quite intersecting with irq-driven governors,
which are being proposed these days.

Although they may look intersecting, we can have them independently;
this as a sub-class and that as a governor. And we can consider to
provide a common infrastructure for irq-driven mechanisms in devfreq or
devfreq-event when we irq-driven DVFS become more general, which I
expect in 2 ~ 3 years.

So for now, both can go independently.


Cheers!
MyungJoo