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Date: Thu, 08 May 2014 12:53:50 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Alan Stern <stern@...land.harvard.edu>,
Linux PM list <linux-pm@...r.kernel.org>,
Mika Westerberg <mika.westerberg@...ux.intel.com>,
Aaron Lu <aaron.lu@...el.com>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/3] PM / sleep: Flag to speed up suspend-resume of runtime-suspended devices
On Thursday, May 08, 2014 09:49:36 AM Ulf Hansson wrote:
> On 8 May 2014 01:29, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.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@...el.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.
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