linux-kernel - Re: [PATCH v6 2/8] cpufreq: Add boost frequency support in core

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Message-id: <20130726121016.6af979ca@amdc308.digital.local>
Date:	Fri, 26 Jul 2013 12:10:16 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <eduardo.valentin@...com>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>, durgadoss.r@...el.com,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH v6 2/8] cpufreq: Add boost frequency support in core

On Fri, 26 Jul 2013 15:03:34 +0530 Viresh Kumar wrote,
> On 26 July 2013 14:03, Lukasz Majewski <l.majewski@...sung.com> wrote:
> > On Fri, 26 Jul 2013 12:47:15 +0530 Viresh Kumar wrote,
> >> On 25 July 2013 22:03, Lukasz Majewski <l.majewski@...sung.com>
> >> wrote:
> 
> >> > +int cpufreq_boost_trigger_state(int state)
> >> > +{
> >> > +       unsigned long flags;
> >> > +       int ret = 0;
> >> > +
> >> > +       if (cpufreq_driver->boost_enabled == state)
> >> > +               return 0;
> >> > +
> >> > +       write_lock_irqsave(&cpufreq_driver_lock, flags);
> >> > +       cpufreq_driver->boost_enabled = state;
> >> > +       write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >             ^^^^^^^^^^^^^^^^^^^^ [*]
> >>
> >> Not sure if we should leave the lock at this point of time, as we
> >> haven't enabled boost until now.
> >
> > The problem here is with the cpufreq_driver->set_boost() call.
> >
> > I tried to avoid acquiring lock at one function and release it at
> > another (in this case cpufreq_boost_set_sw), especially since the
> > __cpufreq_governor() acquires its own lock - good place for
> > deadlock.
> >
> > Is it OK for you to grab lock at one function
> > (cpufreq_boost_trigger_state()) and then at other function
> > (cpufreq_boost_set_sw) release it before calling
> > __cpufreq_governor() and grab it again after its completion?
> 
> >> > +       ret = cpufreq_driver->set_boost(state);
> >> > +       if (ret) {
> >> > +               write_lock_irqsave(&cpufreq_driver_lock, flags);
> >> > +               cpufreq_driver->boost_enabled = 0;
> >>
> >> should be:
> >>                     cpufreq_driver->boost_enabled = !state;
> >
> > For me = 0 (or = false) is more readable.
> > If you wish, I will change it to = !state.
> 
> Its not about readability but logic... What if boost was enabled
> earlier and we are disabling it now.. and we reach here.. We
> need to enable boost again, whereas you are disabling it.

You are right here. I will change this to = !state

> 
> >> > +int cpufreq_boost_supported(void)
> >> > +{
> >> > +       if (cpufreq_driver)
> >>
> >> This routine is always called from places where cpufreq_driver
> >> can't be NULL..
> >
> > It is also called from thermal. And it happens that thermal is
> > initialized earlier.
> > Then "NULL pointer dereference" happens.
> 
> Ok.. Put a likely() around this check for cpufreq_driver..

Ok.

> 
> > In my opinion at [1] we don't need the if (cpufreq_driver) check.
> > But it is up to you to decide.
> 
> leave it as is.

Ok.

> 
> > If we agree about above comments, I will post v7 ASAP.
> 
> Don't post it ASAP, wait for few more days for others to give
> comments.. And also I haven't finished reviewing it until
> now.

Ok.

-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
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