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

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Thursday, May 08, 2014 09:49:36 AM Ulf Hansson wrote:
> On 8 May 2014 01:29, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > 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@intel.com>
> > ---
> >  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,

Well, OK.  I guess we can tolerate one useless statement in rpm_resume()
in case CONFIG_PM_SLEEP is unset.

> and then we could rename the new APIs to pm_runtime_* instead.

That would just make the name longer - for what value?

> >  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?

Actually, no.  The reason is the (*) change in rpm_resume().

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

Yes, it will.

> > +                               __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?

Yes, it is.  We don't want any leftovers after this point.

> >                 mutex_unlock(&dpm_list_mtx);
> >
> >                 error = device_prepare(dev, state);
> >
> > --

Thanks!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.