[PATCH V5 3/9] kernel/cpu_pm: Add runtime PM support for CPUs

[Ulf Hansson]

On 3 March 2017 at 21:41, Lina Iyer <lina.iyer at linaro.org> wrote:
> Notify runtime PM when the CPU is going to be powered off in the idle
> state. This allows for runtime PM suspend/resume of the CPU as well as
> its PM domain.
>
> Cc: Kevin Hilman <khilman at kernel.org>
> Cc: Rafael J. Wysocki <rjw at rjwysocki.net>
> Signed-off-by: Lina Iyer <lina.iyer at linaro.org>
> ---
>  include/linux/cpuhotplug.h |  1 +
>  kernel/cpu_pm.c            | 47 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 48 insertions(+)
>
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index 921acaa..448226a 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -79,6 +79,7 @@ enum cpuhp_state {
>         CPUHP_AP_OFFLINE,
>         CPUHP_AP_SCHED_STARTING,
>         CPUHP_AP_RCUTREE_DYING,
> +       CPUHP_AP_CPU_PM_STARTING,
>         CPUHP_AP_IRQ_GIC_STARTING,
>         CPUHP_AP_IRQ_HIP04_STARTING,
>         CPUHP_AP_IRQ_ARMADA_XP_STARTING,
> diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
> index 009cc9a..db95ef3 100644
> --- a/kernel/cpu_pm.c
> +++ b/kernel/cpu_pm.c
> @@ -16,9 +16,12 @@
>   */
>
>  #include <linux/kernel.h>
> +#include <linux/cpu.h>
> +#include <linux/cpuhotplug.h>
>  #include <linux/cpu_pm.h>
>  #include <linux/module.h>
>  #include <linux/notifier.h>
> +#include <linux/pm_runtime.h>
>  #include <linux/spinlock.h>
>  #include <linux/syscore_ops.h>
>
> @@ -99,6 +102,7 @@ int cpu_pm_enter(void)
>  {
>         int nr_calls;
>         int ret = 0;
> +       struct device *dev = get_cpu_device(smp_processor_id());
>
>         read_lock(&cpu_pm_notifier_lock);
>         ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls);
> @@ -110,6 +114,10 @@ int cpu_pm_enter(void)
>                 cpu_pm_notify(CPU_PM_ENTER_FAILED, nr_calls - 1, NULL);
>         read_unlock(&cpu_pm_notifier_lock);
>
> +       /* Notify Runtime PM that we are suspending the CPU */
> +       if (!ret && dev)
> +               RCU_NONIDLE(pm_runtime_put_sync_suspend(dev));
> +

I am trying to understand how the runtime PM usage count becomes
properly balanced.

I believe you could you end up first calling a
pm_runtime_put_sync_suspend(), without earlier having called
pm_runtime_get*(). I am not sure though, but perhaps you can
elaborate.

Anyway, in patch2/9, where you enable runtime PM there is only a call
to pm_runtime_set_active(), which doesn't increase the usage count. To
me, it seems like that change also needs a pm_runtime_get_noresume().

>         return ret;
>  }
>  EXPORT_SYMBOL_GPL(cpu_pm_enter);
> @@ -129,6 +137,11 @@ EXPORT_SYMBOL_GPL(cpu_pm_enter);
>  int cpu_pm_exit(void)
>  {
>         int ret;
> +       struct device *dev = get_cpu_device(smp_processor_id());
> +
> +       /* Notify Runtime PM that we are resuming the CPU */
> +       if (dev)
> +               RCU_NONIDLE(pm_runtime_get_sync(dev));
>
>         read_lock(&cpu_pm_notifier_lock);
>         ret = cpu_pm_notify(CPU_PM_EXIT, -1, NULL);
> @@ -200,6 +213,40 @@ int cpu_cluster_pm_exit(void)
>  }
>  EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit);
>
> +#ifdef CONFIG_HOTPLUG_CPU
> +static int cpu_pm_cpu_dying(unsigned int cpu)
> +{
> +       struct device *dev = get_cpu_device(cpu);
> +
> +       if (dev)
> +               pm_runtime_put_sync_suspend(dev);
> +
> +       return 0;
> +}
> +
> +static int cpu_pm_cpu_starting(unsigned int cpu)
> +{
> +       struct device *dev = get_cpu_device(cpu);
> +
> +       if (dev)
> +               pm_runtime_get_sync(dev);

I assume that according to my comment above, you somehow need to
compensate for either of the cases when CONFIG_HOTPLUG_CPU is set or
unset. Right?

> +
> +       return 0;
> +}
> +
> +static int __init cpu_pm_hotplug_init(void)
> +{
> +       int ret;
> +
> +       ret = cpuhp_setup_state(CPUHP_AP_CPU_PM_STARTING,
> +                               "AP_CPU_PM_STARTING",
> +                               cpu_pm_cpu_starting, cpu_pm_cpu_dying);
> +
> +       return ret;
> +}
> +device_initcall(cpu_pm_hotplug_init);
> +#endif
> +
>  #ifdef CONFIG_PM
>  static int cpu_pm_suspend(void)
>  {
> --
> 2.7.4
>

Kind regards
Uffe