Re: [RFC][PATCH 1/3] PM / sleep: Flag to speed up suspend-resume of runtime-suspended devices

[Ulf Hansson]

On 8 May 2014 01:29, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> Currently, some subsystems (e.g. PCI and the ACPI PM domain) have to
> resume all runtime-suspended devices during system suspend, mostly
> because those devices may need to be reprogrammed due to different
> wakeup settings for system sleep and for runtime PM.
>
> For some devices, though, it's OK to remain in runtime suspend
> throughout a complete system suspend/resume cycle (if the device was in
> runtime suspend at the start of the cycle).  We would like to do this
> whenever possible, to avoid the overhead of extra power-up and power-down
> events.
>
> However, problems may arise because the device's descendants may require
> it to be at full power at various points during the cycle.  Therefore the
> most straightforward way to do this safely is if the device and all its
> descendants can remain runtime suspended until the resume stage of system
> resume.
>
> To this end, introduce dev->power.leave_runtime_suspended.
> If a subsystem or driver sets this flag during the ->prepare() callback,
> and if the flag is set in all of the device's descendants, and if the
> device is still in runtime suspend at the beginning of the ->suspend()
> callback, that callback is allowed to return 0 without clearing
> power.leave_runtime_suspended and without changing the state of the
> device, unless the current state of the device is not appropriate for
> the upcoming system sleep state (for example, the device is supposed to
> wake up the system from that state and its current wakeup settings are
> not suitable for that).  Then, the PM core will not invoke the device's
> ->suspend_late(), ->suspend_irq(), ->resume_irq(), ->resume_early(), or
> ->resume() callbacks.  Instead, it will invoke ->runtime_resume() during
> the device resume stage of system resume.
>
> By leaving this flag set after ->suspend(), a driver or subsystem tells
> the PM core that the device is runtime suspended, it is in a suitable
> state for system suspend (for example, the wakeup setting does not
> need to be changed), and it does not need to return to full
> power until the resume stage.
>
> Changelog based on an Alan Stern's description of the idea
> (http://marc.info/?l=linux-pm&m=139940466625569&w=2).
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>  drivers/base/power/main.c    |   31 ++++++++++++++++++++++++-------
>  drivers/base/power/runtime.c |   10 ++++++++++
>  include/linux/pm.h           |    3 +++
>  include/linux/pm_runtime.h   |   16 ++++++++++++++++
>  kernel/power/Kconfig         |    4 ++++
>  5 files changed, 57 insertions(+), 7 deletions(-)
>
> Index: linux-pm/kernel/power/Kconfig
> ===================================================================
> --- linux-pm.orig/kernel/power/Kconfig
> +++ linux-pm/kernel/power/Kconfig
> @@ -147,6 +147,10 @@ config PM
>         def_bool y
>         depends on PM_SLEEP || PM_RUNTIME
>
> +config PM_BOTH
> +       def_bool y
> +       depends on PM_SLEEP && PM_RUNTIME
> +

Should we not depend on PM_RUNTIME only? Thus we don't need the new
Kconfig, and then we could rename the new APIs to pm_runtime_*
instead.

>  config PM_DEBUG
>         bool "Power Management Debug Support"
>         depends on PM
> Index: linux-pm/include/linux/pm.h
> ===================================================================
> --- linux-pm.orig/include/linux/pm.h
> +++ linux-pm/include/linux/pm.h
> @@ -583,6 +583,9 @@ struct dev_pm_info {
>         unsigned long           suspended_jiffies;
>         unsigned long           accounting_timestamp;
>  #endif
> +#ifdef CONFIG_PM_BOTH
> +       bool                    leave_runtime_suspended:1;
> +#endif
>         struct pm_subsys_data   *subsys_data;  /* Owned by the subsystem. */
>         void (*set_latency_tolerance)(struct device *, s32);
>         struct dev_pm_qos       *qos;
> Index: linux-pm/include/linux/pm_runtime.h
> ===================================================================
> --- linux-pm.orig/include/linux/pm_runtime.h
> +++ linux-pm/include/linux/pm_runtime.h
> @@ -264,4 +264,20 @@ static inline void pm_runtime_dont_use_a
>         __pm_runtime_use_autosuspend(dev, false);
>  }
>
> +#ifdef CONFIG_PM_BOTH
> +static inline void __set_leave_runtime_suspended(struct device *dev, bool val)
> +{
> +       dev->power.leave_runtime_suspended = val;
> +}
> +extern void pm_set_leave_runtime_suspended(struct device *dev, bool val);
> +static inline bool pm_leave_runtime_suspended(struct device *dev)
> +{
> +       return dev->power.leave_runtime_suspended;
> +}
> +#else
> +static inline void __set_leave_runtime_suspended(struct device *dev, bool val) {}
> +static inline void pm_set_leave_runtime_suspended(struct device *dev, bool val) {}
> +static inline bool pm_leave_runtime_suspended(struct device *dev) { return false; }
> +#endif
> +
>  #endif
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -732,6 +732,7 @@ static int rpm_resume(struct device *dev
>         }
>   skip_parent:
>
> +       __set_leave_runtime_suspended(dev, false);
>         if (dev->power.no_callbacks)
>                 goto no_callback;       /* Assume success. */
>
> @@ -1485,3 +1486,12 @@ out:
>         return ret;
>  }
>  EXPORT_SYMBOL_GPL(pm_runtime_force_resume);
> +
> +#ifdef CONFIG_PM_BOTH
> +void pm_set_leave_runtime_suspended(struct device *dev, bool val)
> +{
> +       spin_lock_irq(&dev->power.lock);
> +       __set_leave_runtime_suspended(dev, val);
> +       spin_unlock_irq(&dev->power.lock);
> +}
> +#endif
> Index: linux-pm/drivers/base/power/main.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/main.c
> +++ linux-pm/drivers/base/power/main.c
> @@ -479,7 +479,7 @@ static int device_resume_noirq(struct de
>         TRACE_DEVICE(dev);
>         TRACE_RESUME(0);
>
> -       if (dev->power.syscore)
> +       if (dev->power.syscore || pm_leave_runtime_suspended(dev))
>                 goto Out;
>
>         if (!dev->power.is_noirq_suspended)
> @@ -605,7 +605,7 @@ static int device_resume_early(struct de
>         TRACE_DEVICE(dev);
>         TRACE_RESUME(0);
>
> -       if (dev->power.syscore)
> +       if (dev->power.syscore || pm_leave_runtime_suspended(dev))
>                 goto Out;
>
>         if (!dev->power.is_late_suspended)
> @@ -735,6 +735,11 @@ static int device_resume(struct device *
>         if (dev->power.syscore)
>                 goto Complete;
>
> +       if (pm_leave_runtime_suspended(dev)) {
> +               pm_runtime_resume(dev);
> +               goto Complete;
> +       }
> +
>         dpm_wait(dev->parent, async);
>         dpm_watchdog_set(&wd, dev);
>         device_lock(dev);
> @@ -1007,7 +1012,7 @@ static int __device_suspend_noirq(struct
>                 goto Complete;
>         }
>
> -       if (dev->power.syscore)
> +       if (dev->power.syscore || pm_leave_runtime_suspended(dev))
>                 goto Complete;
>
>         dpm_wait_for_children(dev, async);
> @@ -1146,7 +1151,7 @@ static int __device_suspend_late(struct
>                 goto Complete;
>         }
>
> -       if (dev->power.syscore)
> +       if (dev->power.syscore || pm_leave_runtime_suspended(dev))
>                 goto Complete;
>
>         dpm_wait_for_children(dev, async);
> @@ -1382,10 +1387,21 @@ static int __device_suspend(struct devic
>
>   End:
>         if (!error) {
> +               struct device *parent = dev->parent;
> +
>                 dev->power.is_suspended = true;
> -               if (dev->power.wakeup_path
> -                   && dev->parent && !dev->parent->power.ignore_children)
> -                       dev->parent->power.wakeup_path = true;
> +               if (parent) {
> +                       spin_lock_irq(&parent->power.lock);
> +
> +                       if (dev->power.wakeup_path
> +                           && !parent->power.ignore_children)
> +                               parent->power.wakeup_path = true;
> +
> +                       if (!pm_leave_runtime_suspended(dev))

I suppose this is the reason to why you think you need CONFIG_PM_BOTH?

But won't this would work nicely even if we just had CONFIG_PM_RUNTIME?

> +                               __set_leave_runtime_suspended(parent, false);
> +
> +                       spin_unlock_irq(&parent->power.lock);
> +               }
>         }
>
>         device_unlock(dev);
> @@ -1553,6 +1569,7 @@ int dpm_prepare(pm_message_t state)
>                 struct device *dev = to_device(dpm_list.next);
>
>                 get_device(dev);
> +               pm_set_leave_runtime_suspended(dev, false);

Is this needed?

>                 mutex_unlock(&dpm_list_mtx);
>
>                 error = device_prepare(dev, state);
>
> --
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Kind regards
Ulf Hansson
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