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    Subject[RFCv5 PATCH 37/46] cpufreq: introduce cpufreq_driver_might_sleep
    Date
    From: Michael Turquette <mturquette@baylibre.com>

    Some architectures and platforms perform CPU frequency transitions
    through a non-blocking method, while some might block or sleep. This
    distinction is important when trying to change frequency from interrupt
    context or in any other non-interruptable context, such as from the
    Linux scheduler.

    Describe this distinction with a cpufreq driver flag,
    CPUFREQ_DRIVER_WILL_NOT_SLEEP. The default is to not have this flag set,
    thus erring on the side of caution.

    cpufreq_driver_might_sleep() is also introduced in this patch. Setting
    the above flag will allow this function to return false.

    Cc: Rafael J. Wysocki <rafael@kernel.org>
    Cc: Viresh Kumar <viresh.kumar@linaro.org>
    Signed-off-by: Michael Turquette <mturquette@baylibre.com>
    ---
    drivers/cpufreq/cpufreq.c | 6 ++++++
    include/linux/cpufreq.h | 9 +++++++++
    2 files changed, 15 insertions(+)

    diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
    index 8ae655c..5753cb6 100644
    --- a/drivers/cpufreq/cpufreq.c
    +++ b/drivers/cpufreq/cpufreq.c
    @@ -112,6 +112,12 @@ bool have_governor_per_policy(void)
    }
    EXPORT_SYMBOL_GPL(have_governor_per_policy);

    +bool cpufreq_driver_might_sleep(void)
    +{
    + return !(cpufreq_driver->flags & CPUFREQ_DRIVER_WILL_NOT_SLEEP);
    +}
    +EXPORT_SYMBOL_GPL(cpufreq_driver_might_sleep);
    +
    struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy)
    {
    if (have_governor_per_policy())
    diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
    index 2ee4888..1f2c9a1 100644
    --- a/include/linux/cpufreq.h
    +++ b/include/linux/cpufreq.h
    @@ -157,6 +157,7 @@ u64 get_cpu_idle_time(unsigned int cpu, u64 *wall, int io_busy);
    int cpufreq_get_policy(struct cpufreq_policy *policy, unsigned int cpu);
    int cpufreq_update_policy(unsigned int cpu);
    bool have_governor_per_policy(void);
    +bool cpufreq_driver_might_sleep(void);
    struct kobject *get_governor_parent_kobj(struct cpufreq_policy *policy);
    #else
    static inline unsigned int cpufreq_get(unsigned int cpu)
    @@ -314,6 +315,14 @@ struct cpufreq_driver {
    */
    #define CPUFREQ_NEED_INITIAL_FREQ_CHECK (1 << 5)

    +/*
    + * Set by drivers that will never block or sleep during their frequency
    + * transition. Used to indicate when it is safe to call cpufreq_driver_target
    + * from non-interruptable context. Drivers must opt-in to this flag, as the
    + * safe default is that they might sleep.
    + */
    +#define CPUFREQ_DRIVER_WILL_NOT_SLEEP (1 << 6)
    +
    int cpufreq_register_driver(struct cpufreq_driver *driver_data);
    int cpufreq_unregister_driver(struct cpufreq_driver *driver_data);

    --
    1.9.1


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