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    SubjectRe: [PATCH v6 2/8] cpufreq: Add boost frequency support in core
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    On Friday, July 26, 2013 10:33:21 AM Lukasz Majewski wrote:
    > 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?

    It generally is better to avoid doing that, although it is not unheard of.

    Thanks,
    Rafael


    --
    I speak only for myself.
    Rafael J. Wysocki, Intel Open Source Technology Center.


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