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

Lukasz Majewski
2013-07-26T08:33:21Z

On Fri, 26 Jul 2013 12:47:15 +0530 Viresh Kumar wrote,
> On 25 July 2013 22:03, Lukasz Majewski <l.majewski@samsung.com> wrote:
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>
> > /*********************************************************************
> > + *
> > BOOST *
> > +
> > *********************************************************************/
> > +static int cpufreq_boost_set_sw(int state) +{
> > + struct cpufreq_frequency_table *freq_table;
> > + struct cpufreq_policy *policy;
> > + int ret = -EINVAL;
> > +
> > + list_for_each_entry(policy, &cpufreq_policy_list,
> > policy_list) {
> > + freq_table =
> > cpufreq_frequency_get_table(policy->cpu);
> > + if (freq_table) {
> > + ret =
> > cpufreq_frequency_table_cpuinfo(policy,
> > + freq_table);
> > + if (!ret) {
> > + policy->user_policy.max =
> > policy->max;
> > + __cpufreq_governor(policy,
> > CPUFREQ_GOV_LIMITS);
> > + }
> > + }
> > + }
> > +
> > + return ret;
> > +}
> > +
> > +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?

>
> If somebody tries to use this variable at this point of time, then
> it would get the wrong information about it.
>
> > + 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.

>
> > + write_unlock_irqrestore(&cpufreq_driver_lock,
> > flags); +
> > + pr_err("%s: BOOST cannot %s\n", __func__,
>
> s/BOOST cannot %s/Cannot %s BOOST

Ok.

>
> > + state ? "enabled" : "disabled");
> > + }
> > +
> > + return ret;
> > +}
> > +
> > +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.

>
> --contd--
>
> > + return cpufreq_driver->boost_supported;
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(cpufreq_boost_supported);
> > +
> > +int cpufreq_boost_enabled(void)
> > +{
> > + return cpufreq_driver->boost_enabled;
^^^^^^^^^^^^^^ [1]

>
> And if above check is necessary, then don't you need to check
> it here as well?

Because on thermal I check first if cpufreq_boost_supported() is true.
If boost is not supported then check for cpufreq_boost_enabled() is not
performed.

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

>
> > +}
> > +EXPORT_SYMBOL_GPL(cpufreq_boost_enabled);
> > +
> > +/*********************************************************************
> > * REGISTER / UNREGISTER CPUFREQ
> > DRIVER *
> > *********************************************************************/
> >
> > @@ -2008,9 +2099,25 @@ int cpufreq_register_driver(struct
> > cpufreq_driver *driver_data) cpufreq_driver = driver_data;
> > write_unlock_irqrestore(&cpufreq_driver_lock, flags);
> >
> > + if (cpufreq_boost_supported()) {
> > + /*
> > + * Check if boost driver provides function to
> > enable boost -
>
> s/boost driver/driver

Ok.

>
> > + * if not, use cpufreq_boost_set_sw as default
> > + */
> > + if (!cpufreq_driver->set_boost)
> > + cpufreq_driver->set_boost =
> > cpufreq_boost_set_sw; +
> > + ret = cpufreq_sysfs_create_file(&(boost.attr));
>
> You don't need braces around boost.attr.

Ok.

>
> > + if (ret) {
> > + pr_err("%s: cannot register global BOOST
> > sysfs file\n",
> > + __func__);
> > + goto err_null_driver;
> > + }
> > + }
> > +
> > ret = subsys_interface_register(&cpufreq_interface);
> > if (ret)
> > - goto err_null_driver;
> > + goto err_boost_unreg;
> >
> > if (!(cpufreq_driver->flags & CPUFREQ_STICKY)) {
> > int i;
> > @@ -2037,6 +2144,9 @@ int cpufreq_register_driver(struct
> > cpufreq_driver *driver_data) return 0;
> > err_if_unreg:
> > subsys_interface_unregister(&cpufreq_interface);
> > +err_boost_unreg:
> > + if (cpufreq_boost_supported())
> > + cpufreq_sysfs_remove_file(&(boost.attr));
>
> same here.

Ok.

>
> > err_null_driver:
> > write_lock_irqsave(&cpufreq_driver_lock, flags);
> > cpufreq_driver = NULL;
> > @@ -2063,6 +2173,9 @@ int cpufreq_unregister_driver(struct
> > cpufreq_driver *driver) pr_debug("unregistering driver %s\n",
> > driver->name);
> >
> > subsys_interface_unregister(&cpufreq_interface);
> > + if (cpufreq_boost_supported())
> > + cpufreq_sysfs_remove_file(&(boost.attr));
>
> here too.

Ok.

>
> > +
> > unregister_hotcpu_notifier(&cpufreq_cpu_notifier);
> >
> > write_lock_irqsave(&cpufreq_driver_lock, flags);
>
> > +static ssize_t scaling_available_frequencies_show(struct
> > cpufreq_policy *policy,
> > + char *buf)
> > +{
> > + return show_available_freqs(policy, buf, 0);
>
> s/0/false

Ok.

>
> > +}
>
> > +static ssize_t scaling_boost_frequencies_show(struct
> > cpufreq_policy *policy,
> > + char *buf)
> > +{
> > + return show_available_freqs(policy, buf, 1);
>
> s/1/true

Ok.

>
> > +}
>
> Looks good mostly.. We Should be to get it in 3.12 :)

If we agree about above comments, I will post v7 ASAP.

--
Best regards,

Lukasz Majewski

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