linux-kernel - Re: [PATCH 1/5] cpufreq: Define cpufreq_set_drv_attr

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Date:	Thu, 06 Jun 2013 10:58:14 +0200
From:	Lukasz Majewski <l.majewski@...sung.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	"Rafael J. Wysocky" <rjw@...k.pl>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	Myungjoo Ham <myungjoo.ham@...sung.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Lukasz Majewski <l.majewski@...ess.pl>,
	Andre Przywara <andre.przywara@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH 1/5] cpufreq: Define cpufreq_set_drv_attr_files() to add
 per CPU sysfs attributes

Hi Viresh,

> On 6 June 2013 12:37, Lukasz Majewski <l.majewski@...sung.com> wrote:
> 
> > Subject: cpufreq: Define cpufreq_set_drv_attr_files() to add per
> > CPU sysfs attributes
> 
> Its not per-cpu. We just add it for policy->cpu and other routines
> actually create links.
> 
> > The cpufreq_set_drv_attr_files() function creates sysfs file entry
> > for each available CPU. With it in place it is possible to add
> > different set of attributes without code duplication.
> 
> Not for each available cpu but are linked to a policy->kobj and so
> shows up on each policy->cpus.

Yes, you are right here. Thanks for detailed explanation. Being
"per-cpu" comes from kobj embedded at policy, which has information
about cpus affected. 

> 
> > Signed-off-by: Lukasz Majewski <l.majewski@...sung.com>
> > Signed-off-by: Myungjoo Ham <myungjoo.ham@...sung.com>
> > ---
> >  drivers/cpufreq/cpufreq.c |   23 +++++++++++++++--------
> >  1 file changed, 15 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 1b8a48e..ca74e27 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -730,12 +730,23 @@ static int cpufreq_add_dev_symlink(unsigned
> > int cpu, return ret;
> >  }
> >
> > +static int cpufreq_set_drv_attr_files(struct cpufreq_policy
> > *policy,
> > +                                     struct freq_attr **drv_attr)
> > +{
> > +       while ((drv_attr) && (*drv_attr)) {
> > +               if (sysfs_create_file(&policy->kobj,
> > &((*drv_attr)->attr)))
> > +                       return 1;
> 
> You are changing the semantics here. We used to return error
> value from sysfs_create_file() and you are returning 1.

Yes, correct. The ret from sysfs_create_file shall be returned.
Returning 1 causes information lost.

> 
> > +               drv_attr++;
> 
> If drv_attr was valid initially, then drv_attr++ can't make it NULL.
> So, we don't need to check validity of drv_attr for every loop.

I'm confused here. 

So you want to check dev_attr for NULL just after:
drv_attr = cpufreq_driver->attr;
if (!drv_attr)
	goto error;

and skip the check at the while loop:
while ((drv_attr) && (*drv_attr)) 

to 

while ((*drv_attr))

Am I correct?


-- 
Best regards,

Lukasz Majewski

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