Re: [PATCH v2 4/4] PM: sleep: Avoid unnecessary checks in device_prepare_smart_suspend()

[Ulf Hansson]

On Tue, 18 Feb 2025 at 21:20, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> Add an optimization (on top of previous changes) to avoid calling
> pm_runtime_blocked(), which involves acquiring the device's PM spinlock,
> for devices with no PM callbacks and runtime PM "blocked".
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>

Kind regards
Uffe

> ---
>  drivers/base/power/main.c    |   16 +++++++++-------
>  drivers/base/power/runtime.c |    9 +++++++--
>  include/linux/pm_runtime.h   |    4 ++--
>  3 files changed, 18 insertions(+), 11 deletions(-)
>
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -1796,16 +1796,14 @@
>
>         /*
>          * The "smart suspend" feature is enabled for devices whose drivers ask
> -        * for it and for devices without PM callbacks unless runtime PM is
> -        * disabled and enabling it is blocked for them.
> +        * for it and for devices without PM callbacks.
>          *
>          * However, if "smart suspend" is not enabled for the device's parent
>          * or any of its suppliers that take runtime PM into account, it cannot
>          * be enabled for the device either.
>          */
> -       dev->power.smart_suspend = (dev->power.no_pm_callbacks ||
> -               dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND)) &&
> -               !pm_runtime_blocked(dev);
> +       dev->power.smart_suspend = dev->power.no_pm_callbacks ||
> +               dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND);
>
>         if (!dev_pm_smart_suspend(dev))
>                 return;
> @@ -1843,6 +1841,7 @@
>  static int device_prepare(struct device *dev, pm_message_t state)
>  {
>         int (*callback)(struct device *) = NULL;
> +       bool no_runtime_pm;
>         int ret = 0;
>
>         /*
> @@ -1858,7 +1857,7 @@
>          * suspend-resume cycle is complete, so prepare to trigger a warning on
>          * subsequent attempts to enable it.
>          */
> -       pm_runtime_block_if_disabled(dev);
> +       no_runtime_pm = pm_runtime_block_if_disabled(dev);
>
>         if (dev->power.syscore)
>                 return 0;
> @@ -1893,7 +1892,10 @@
>                 pm_runtime_put(dev);
>                 return ret;
>         }
> -       device_prepare_smart_suspend(dev);
> +       /* Do not enable "smart suspend" for devices without runtime PM. */
> +       if (!no_runtime_pm)
> +               device_prepare_smart_suspend(dev);
> +
>         /*
>          * A positive return value from ->prepare() means "this device appears
>          * to be runtime-suspended and its state is fine, so if it really is
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1460,14 +1460,19 @@
>  }
>  EXPORT_SYMBOL_GPL(pm_runtime_barrier);
>
> -void pm_runtime_block_if_disabled(struct device *dev)
> +bool pm_runtime_block_if_disabled(struct device *dev)
>  {
> +       bool ret;
> +
>         spin_lock_irq(&dev->power.lock);
>
> -       if (dev->power.disable_depth && dev->power.last_status == RPM_INVALID)
> +       ret = dev->power.disable_depth && dev->power.last_status == RPM_INVALID;
> +       if (ret)
>                 dev->power.last_status = RPM_BLOCKED;
>
>         spin_unlock_irq(&dev->power.lock);
> +
> +       return ret;
>  }
>
>  void pm_runtime_unblock(struct device *dev)
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -77,7 +77,7 @@
>  extern int pm_schedule_suspend(struct device *dev, unsigned int delay);
>  extern int __pm_runtime_set_status(struct device *dev, unsigned int status);
>  extern int pm_runtime_barrier(struct device *dev);
> -extern void pm_runtime_block_if_disabled(struct device *dev);
> +extern bool pm_runtime_block_if_disabled(struct device *dev);
>  extern void pm_runtime_unblock(struct device *dev);
>  extern void pm_runtime_enable(struct device *dev);
>  extern void __pm_runtime_disable(struct device *dev, bool check_resume);
> @@ -274,7 +274,7 @@
>  static inline int __pm_runtime_set_status(struct device *dev,
>                                             unsigned int status) { return 0; }
>  static inline int pm_runtime_barrier(struct device *dev) { return 0; }
> -static inline void pm_runtime_block_if_disabled(struct device *dev) {}
> +static inline bool pm_runtime_block_if_disabled(struct device *dev) { return true; }
>  static inline void pm_runtime_unblock(struct device *dev) {}
>  static inline void pm_runtime_enable(struct device *dev) {}
>  static inline void __pm_runtime_disable(struct device *dev, bool c) {}
>
>
>