linux-kernel - Re: [RFCv5 PATCH 37/46] cpufreq: introduce cpufreq_driver_might

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Date:	Wed, 08 Jul 2015 08:09:14 -0700
From:	Michael Turquette <mturquette@...libre.com>
To:	Morten Rasmussen <morten.rasmussen@....com>, peterz@...radead.org,
	mingo@...hat.com
Cc:	vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
	"Dietmar Eggemann" <Dietmar.Eggemann@....com>, yuyang.du@...el.com,
	rjw@...ysocki.net, "Juri Lelli" <Juri.Lelli@....com>,
	sgurrappadi@...dia.com, pang.xunlei@....com.cn,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Viresh Kumar" <viresh.kumar@...aro.org>
Subject: Re: [RFCv5 PATCH 37/46] cpufreq: introduce cpufreq_driver_might_sleep

Quoting Morten Rasmussen (2015-07-07 11:24:20)
> From: Michael Turquette <mturquette@...libre.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@...nel.org>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Michael Turquette <mturquette@...libre.com>

Hi Morten,

I believe your sign-off is needed here as well.

Regards,
Mike

> ---
>  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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