linux-kernel - Re: [PATCH v4 2/7] cpufreq: Add boost frequency support in core

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Date:	Wed, 19 Jun 2013 22:31:02 +0200
From:	Lukasz Majewski <l.majewski@...ess.pl>
To:	Dirk Brandewie <dirk.brandewie@...il.com>
Cc:	Lukasz Majewski <l.majewski@...sung.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"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>,
	Andre Przywara <andre.przywara@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <eduardo.valentin@...com>
Subject: Re: [PATCH v4 2/7] cpufreq: Add boost frequency support in core

On Wed, 19 Jun 2013 10:48:53 -0700
Dirk Brandewie <dirk.brandewie@...il.com> wrote:

> On 06/19/2013 10:12 AM, Lukasz Majewski wrote:
> > This commit adds boost frequency support in cpufreq core (Hardware &
> 
> > +/*********************************************************************
> >    *               REGISTER / UNREGISTER CPUFREQ
> > DRIVER                *
> > *********************************************************************/
> >
> > @@ -1936,6 +2019,16 @@ int cpufreq_register_driver(struct
> > cpufreq_driver *driver_data) cpufreq_driver = driver_data;
> >   	write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >
> > +	if (!cpufreq_driver->boost_supported)
> > +		boost.attr.mode = 0444;
> > +
> > +	ret = cpufreq_sysfs_create_file(&(boost.attr));
> > +	if (ret) {
> > +		pr_err("%s: cannot register global boost sysfs
> > file\n",
> > +		       __func__);
> > +		goto err_null_driver;
> > +	}
> > +
> 
> I do not think the boost sysfs should be created at all if boost is
> not supported.

This was my first thought. But unfortunately this "boost" attribute is
always exported at acpi-cpufreq.c and in my opinion is part of a
legacy API.

I totally agree with the idea of exporting boost only when supported,
but I would like to know the community opinion about this (especially
Viresh and Rafael shall speak up).

> 
> For intel_pstate the read-only boost would be there for no reason and
> would cause confusion on the part of the user IMHO

You are probably right here. However I don't know what was the
original rationale behind exporting this attribute as read only. 

> 
> >   	ret = subsys_interface_register(&cpufreq_interface);
> >   	if (ret)
> >   		goto err_null_driver;
> > @@ -1992,6 +2085,8 @@ int cpufreq_unregister_driver(struct
> > cpufreq_driver *driver) pr_debug("unregistering driver %s\n",
> > driver->name);
> >
> >   	subsys_interface_unregister(&cpufreq_interface);
> > +
> > +	cpufreq_sysfs_remove_file(&(boost.attr));
> >   	unregister_hotcpu_notifier(&cpufreq_cpu_notifier);
> >
> 

Best regards,

Lukasz Majewski

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