linux-kernel - RE: [PATCH 1/3] PM / OPP: Add support for descending order for cpufreq table

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Date:	Thu, 08 May 2014 11:07:24 +0900
From:	Jonghwan Choi <jhbird.choi@...sung.com>
To:	'Nishanth Menon' <nm@...com>
Cc:	'Viresh Kumar' <viresh.kumar@...aro.org>,
	'Linux PM list' <linux-pm@...r.kernel.org>,
	'open list' <linux-kernel@...r.kernel.org>,
	"'Rafael J. Wysocki'" <rjw@...ysocki.net>,
	'Len Brown' <len.brown@...el.com>,
	'Amit Daniel Kachhap' <amit.daniel@...sung.com>
Subject: RE: [PATCH 1/3] PM / OPP: Add support for descending order for cpufreq
 table

I believe that 3 item is required for DVFS. Those are frequency, voltage, divider value.
Currently OPP only supports voltage and frequency. 
So some cpufreq and devfreq driver get a divider value from struct divider table.

How about adding that divider value into struct dev_pm_opp like this;

struct dev_pm_opp {
        struct list_head node;

        bool available;
        unsigned long rate;
        unsigned long u_volt;
        unsigned int ctl[2]; // Added

        struct device_opp *dev_opp;
        struct rcu_head head;
};
In my test, it works very wel..

I got a this idea from _PCT in acpi spec.

Then we can remove a lot of code related to divide table. And we also can solve this problem.

Thanks

Best Regarfs.


> -----Original Message-----
> From: menon.nishanth@...il.com [mailto:menon.nishanth@...il.com] On Behalf
> Of Nishanth Menon
> Sent: Thursday, May 08, 2014 10:56 AM
> To: Jonghwan Choi
> Cc: Viresh Kumar; Linux PM list; open list; Rafael J. Wysocki; Len Brown;
> Amit Daniel Kachhap
> Subject: Re: [PATCH 1/3] PM / OPP: Add support for descending order for
> cpufreq table
> 
> On Wed, May 7, 2014 at 8:22 PM, Jonghwan Choi <jhbird.choi@...sung.com>
> wrote:
> >> @Jonghwan: Please consider doing this:
> >> - Don't play with the order of frequencies in table.
> >> - Instead initialize .driver_data filed with values that you need to
> >> write in the registers for all frequencies. i.e. 0 for highest
> >> frequency and
> >> FREQ_COUNT-1 for lowest one.
> >
> > -> For that, I changed like this.
> > For initializing .driver_data, I changed dev_pm_opp_init_cpufreq_table
> function().
> >
> >
> > --- a/drivers/base/power/opp.c
> > +++ b/drivers/base/power/opp.c
> > @@ -622,12 +622,12 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_disable);
> >   * or in contexts where mutex locking cannot be used.
> >   */
> >  int dev_pm_opp_init_cpufreq_table(struct device *dev,
> > -                           struct cpufreq_frequency_table **table)
> > +               struct cpufreq_frequency_table **table, int order)
> >  {
> >         struct device_opp *dev_opp;
> >         struct dev_pm_opp *opp;
> >         struct cpufreq_frequency_table *freq_table;
> > -       int i = 0;
> > +       int i = 0, index = 0;
> >
> >         /* Pretend as if I am an updater */
> >         mutex_lock(&dev_opp_list_lock); @@ -649,16 +649,22 @@ int
> > dev_pm_opp_init_cpufreq_table(struct device *dev,
> >                 return -ENOMEM;
> >         }
> >
> > +       if (OPP_TABLE_ORDER_DESCENDING == order)
> > +               index = dev_pm_opp_get_opp_count(dev) - 1;
> > +
> >         list_for_each_entry(opp, &dev_opp->opp_list, node) {
> >                 if (opp->available) {
> > -                       freq_table[i].driver_data = i;
> > +                       if (OPP_TABLE_ORDER_DESCENDING == order)
> > +                               freq_table[i].driver_data = index--;
> > +                       else
> > +                               freq_table[i].driver_data = index++;
> >                         freq_table[i].frequency = opp->rate / 1000;
> >                         i++;
> >                 }
> >         }
> >         mutex_unlock(&dev_opp_list_lock);
> >
> > -       freq_table[i].driver_data = i;
> > +       freq_table[i].driver_data = index;
> >         freq_table[i].frequency = CPUFREQ_TABLE_END;
> >
> >         *table = &freq_table[0];
> >
> >
> > Is it acceptiable?
> 
> Personally, I feel that filling up driver_data should be left to the
> driver(caller of dev_pm_opp_init_cpufreq_table). for example providing a
> function pointer which decides what that value should be (be it index or
> some magical register value).. Viresh might have better opinions.
> 
> Regards,
> Nishanth Menon

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